diff --git a/src/librustc/back/archive.rs b/src/librustc/back/archive.rs
index a47b6860014..dd1c754c257 100644
--- a/src/librustc/back/archive.rs
+++ b/src/librustc/back/archive.rs
@@ -28,8 +28,8 @@ use syntax::abi;
 
 pub static METADATA_FILENAME: &'static str = "rust.metadata.bin";
 
-pub struct Archive {
-    priv sess: Session,
+pub struct Archive<'a> {
+    priv sess: &'a Session,
     priv dst: Path,
 }
 
@@ -37,8 +37,8 @@ pub struct ArchiveRO {
     priv ptr: ArchiveRef,
 }
 
-fn run_ar(sess: Session, args: &str, cwd: Option<&Path>,
-        paths: &[&Path]) -> ProcessOutput {
+fn run_ar(sess: &Session, args: &str, cwd: Option<&Path>,
+          paths: &[&Path]) -> ProcessOutput {
     let ar = get_ar_prog(sess);
 
     let mut args = vec!(args.to_owned());
@@ -74,16 +74,16 @@ fn run_ar(sess: Session, args: &str, cwd: Option<&Path>,
     }
 }
 
-impl Archive {
+impl<'a> Archive<'a> {
     /// Initializes a new static archive with the given object file
-    pub fn create<'a>(sess: Session, dst: &'a Path,
-                      initial_object: &'a Path) -> Archive {
+    pub fn create<'b>(sess: &'a Session, dst: &'b Path,
+                      initial_object: &'b Path) -> Archive<'a> {
         run_ar(sess, "crus", None, [dst, initial_object]);
         Archive { sess: sess, dst: dst.clone() }
     }
 
     /// Opens an existing static archive
-    pub fn open(sess: Session, dst: Path) -> Archive {
+    pub fn open(sess: &'a Session, dst: Path) -> Archive<'a> {
         assert!(dst.exists());
         Archive { sess: sess, dst: dst }
     }
diff --git a/src/librustc/back/link.rs b/src/librustc/back/link.rs
index d68fa0ca241..6d5f95b52ab 100644
--- a/src/librustc/back/link.rs
+++ b/src/librustc/back/link.rs
@@ -54,7 +54,7 @@ pub enum OutputType {
     OutputTypeExe,
 }
 
-pub fn llvm_err(sess: Session, msg: ~str) -> ! {
+pub fn llvm_err(sess: &Session, msg: ~str) -> ! {
     unsafe {
         let cstr = llvm::LLVMRustGetLastError();
         if cstr == ptr::null() {
@@ -68,7 +68,7 @@ pub fn llvm_err(sess: Session, msg: ~str) -> ! {
 }
 
 pub fn WriteOutputFile(
-        sess: Session,
+        sess: &Session,
         target: lib::llvm::TargetMachineRef,
         pm: lib::llvm::PassManagerRef,
         m: ModuleRef,
@@ -125,7 +125,7 @@ pub mod write {
         }
     }
 
-    pub fn run_passes(sess: Session,
+    pub fn run_passes(sess: &Session,
                       trans: &CrateTranslation,
                       output_types: &[OutputType],
                       output: &OutputFilenames) {
@@ -156,7 +156,7 @@ pub mod write {
 
             let tm = sess.targ_cfg.target_strs.target_triple.with_c_str(|t| {
                 sess.opts.cg.target_cpu.with_c_str(|cpu| {
-                    target_feature(&sess).with_c_str(|features| {
+                    target_feature(sess).with_c_str(|features| {
                         llvm::LLVMRustCreateTargetMachine(
                             t, cpu, features,
                             lib::llvm::CodeModelDefault,
@@ -323,7 +323,7 @@ pub mod write {
         }
     }
 
-    pub fn run_assembler(sess: Session, outputs: &OutputFilenames) {
+    pub fn run_assembler(sess: &Session, outputs: &OutputFilenames) {
         let cc = super::get_cc_prog(sess);
         let assembly = outputs.temp_path(OutputTypeAssembly);
         let object = outputs.path(OutputTypeObject);
@@ -351,7 +351,7 @@ pub mod write {
         }
     }
 
-    unsafe fn configure_llvm(sess: Session) {
+    unsafe fn configure_llvm(sess: &Session) {
         use sync::one::{Once, ONCE_INIT};
         static mut INIT: Once = ONCE_INIT;
 
@@ -719,7 +719,7 @@ pub fn output_lib_filename(id: &CrateId) -> ~str {
     format!("{}-{}-{}", id.name, crate_id_hash(id), id.version_or_default())
 }
 
-pub fn get_cc_prog(sess: Session) -> ~str {
+pub fn get_cc_prog(sess: &Session) -> ~str {
     match sess.opts.cg.linker {
         Some(ref linker) => return linker.to_owned(),
         None => {}
@@ -737,7 +737,7 @@ pub fn get_cc_prog(sess: Session) -> ~str {
     get_system_tool(sess, "cc")
 }
 
-pub fn get_ar_prog(sess: Session) -> ~str {
+pub fn get_ar_prog(sess: &Session) -> ~str {
     match sess.opts.cg.ar {
         Some(ref ar) => return ar.to_owned(),
         None => {}
@@ -746,7 +746,7 @@ pub fn get_ar_prog(sess: Session) -> ~str {
     get_system_tool(sess, "ar")
 }
 
-fn get_system_tool(sess: Session, tool: &str) -> ~str {
+fn get_system_tool(sess: &Session, tool: &str) -> ~str {
     match sess.targ_cfg.os {
         abi::OsAndroid => match sess.opts.cg.android_cross_path {
             Some(ref path) => {
@@ -765,7 +765,7 @@ fn get_system_tool(sess: Session, tool: &str) -> ~str {
     }
 }
 
-fn remove(sess: Session, path: &Path) {
+fn remove(sess: &Session, path: &Path) {
     match fs::unlink(path) {
         Ok(..) => {}
         Err(e) => {
@@ -776,7 +776,7 @@ fn remove(sess: Session, path: &Path) {
 
 /// Perform the linkage portion of the compilation phase. This will generate all
 /// of the requested outputs for this compilation session.
-pub fn link_binary(sess: Session,
+pub fn link_binary(sess: &Session,
                    trans: &CrateTranslation,
                    outputs: &OutputFilenames,
                    id: &CrateId) -> Vec<Path> {
@@ -830,7 +830,7 @@ pub fn filename_for_input(sess: &Session, crate_type: session::CrateType,
     }
 }
 
-fn link_binary_output(sess: Session,
+fn link_binary_output(sess: &Session,
                       trans: &CrateTranslation,
                       crate_type: session::CrateType,
                       outputs: &OutputFilenames,
@@ -840,7 +840,7 @@ fn link_binary_output(sess: Session,
         Some(ref file) => file.clone(),
         None => {
             let out_filename = outputs.path(OutputTypeExe);
-            filename_for_input(&sess, crate_type, id, &out_filename)
+            filename_for_input(sess, crate_type, id, &out_filename)
         }
     };
 
@@ -883,10 +883,10 @@ fn link_binary_output(sess: Session,
 // rlib primarily contains the object file of the crate, but it also contains
 // all of the object files from native libraries. This is done by unzipping
 // native libraries and inserting all of the contents into this archive.
-fn link_rlib(sess: Session,
-             trans: Option<&CrateTranslation>, // None == no metadata/bytecode
-             obj_filename: &Path,
-             out_filename: &Path) -> Archive {
+fn link_rlib<'a>(sess: &'a Session,
+                 trans: Option<&CrateTranslation>, // None == no metadata/bytecode
+                 obj_filename: &Path,
+                 out_filename: &Path) -> Archive<'a> {
     let mut a = Archive::create(sess, out_filename, obj_filename);
 
     let used_libraries = sess.cstore.get_used_libraries();
@@ -985,7 +985,7 @@ fn link_rlib(sess: Session,
 // There's no need to include metadata in a static archive, so ensure to not
 // link in the metadata object file (and also don't prepare the archive with a
 // metadata file).
-fn link_staticlib(sess: Session, obj_filename: &Path, out_filename: &Path) {
+fn link_staticlib(sess: &Session, obj_filename: &Path, out_filename: &Path) {
     let mut a = link_rlib(sess, None, obj_filename, out_filename);
     a.add_native_library("morestack").unwrap();
     a.add_native_library("compiler-rt").unwrap();
@@ -1016,7 +1016,7 @@ fn link_staticlib(sess: Session, obj_filename: &Path, out_filename: &Path) {
 //
 // This will invoke the system linker/cc to create the resulting file. This
 // links to all upstream files as well.
-fn link_natively(sess: Session, dylib: bool, obj_filename: &Path,
+fn link_natively(sess: &Session, dylib: bool, obj_filename: &Path,
                  out_filename: &Path) {
     let tmpdir = TempDir::new("rustc").expect("needs a temp dir");
     // The invocations of cc share some flags across platforms
@@ -1066,7 +1066,7 @@ fn link_natively(sess: Session, dylib: bool, obj_filename: &Path,
     }
 }
 
-fn link_args(sess: Session,
+fn link_args(sess: &Session,
              dylib: bool,
              tmpdir: &Path,
              obj_filename: &Path,
@@ -1248,7 +1248,7 @@ fn link_args(sess: Session,
 // Also note that the native libraries linked here are only the ones located
 // in the current crate. Upstream crates with native library dependencies
 // may have their native library pulled in above.
-fn add_local_native_libraries(args: &mut Vec<~str> , sess: Session) {
+fn add_local_native_libraries(args: &mut Vec<~str>, sess: &Session) {
     let addl_lib_search_paths = sess.opts.addl_lib_search_paths.borrow();
     for path in addl_lib_search_paths.get().iter() {
         // FIXME (#9639): This needs to handle non-utf8 paths
@@ -1281,7 +1281,7 @@ fn add_local_native_libraries(args: &mut Vec<~str> , sess: Session) {
 // Rust crates are not considered at all when creating an rlib output. All
 // dependencies will be linked when producing the final output (instead of
 // the intermediate rlib version)
-fn add_upstream_rust_crates(args: &mut Vec<~str> , sess: Session,
+fn add_upstream_rust_crates(args: &mut Vec<~str>, sess: &Session,
                             dylib: bool, tmpdir: &Path) {
 
     // As a limitation of the current implementation, we require that everything
@@ -1376,8 +1376,8 @@ fn add_upstream_rust_crates(args: &mut Vec<~str> , sess: Session,
     }
 
     // Adds the static "rlib" versions of all crates to the command line.
-    fn add_static_crates(args: &mut Vec<~str> , sess: Session, tmpdir: &Path,
-                         crates: Vec<(ast::CrateNum, Path)> ) {
+    fn add_static_crates(args: &mut Vec<~str>, sess: &Session, tmpdir: &Path,
+                         crates: Vec<(ast::CrateNum, Path)>) {
         for (cnum, cratepath) in crates.move_iter() {
             // When performing LTO on an executable output, all of the
             // bytecode from the upstream libraries has already been
@@ -1423,7 +1423,7 @@ fn add_upstream_rust_crates(args: &mut Vec<~str> , sess: Session,
     }
 
     // Same thing as above, but for dynamic crates instead of static crates.
-    fn add_dynamic_crates(args: &mut Vec<~str> , sess: Session,
+    fn add_dynamic_crates(args: &mut Vec<~str>, sess: &Session,
                           crates: Vec<(ast::CrateNum, Path)> ) {
         // If we're performing LTO, then it should have been previously required
         // that all upstream rust dependencies were available in an rlib format.
@@ -1458,7 +1458,7 @@ fn add_upstream_rust_crates(args: &mut Vec<~str> , sess: Session,
 // generic function calls a native function, then the generic function must
 // be instantiated in the target crate, meaning that the native symbol must
 // also be resolved in the target crate.
-fn add_upstream_native_libraries(args: &mut Vec<~str> , sess: Session) {
+fn add_upstream_native_libraries(args: &mut Vec<~str>, sess: &Session) {
     let cstore = sess.cstore;
     cstore.iter_crate_data(|cnum, _| {
         let libs = csearch::get_native_libraries(cstore, cnum);
diff --git a/src/librustc/back/lto.rs b/src/librustc/back/lto.rs
index c0d18672a9b..b42e8f1b92e 100644
--- a/src/librustc/back/lto.rs
+++ b/src/librustc/back/lto.rs
@@ -18,7 +18,7 @@ use util::common::time;
 use std::libc;
 use flate;
 
-pub fn run(sess: session::Session, llmod: ModuleRef,
+pub fn run(sess: &session::Session, llmod: ModuleRef,
            tm: TargetMachineRef, reachable: &[~str]) {
     if sess.opts.cg.prefer_dynamic {
         sess.err("cannot prefer dynamic linking when performing LTO");
diff --git a/src/librustc/back/rpath.rs b/src/librustc/back/rpath.rs
index 9b543bb50cc..e4052f8cd6f 100644
--- a/src/librustc/back/rpath.rs
+++ b/src/librustc/back/rpath.rs
@@ -9,7 +9,7 @@
 // except according to those terms.
 
 
-use driver::session;
+use driver::session::Session;
 use metadata::cstore;
 use metadata::filesearch;
 
@@ -22,7 +22,7 @@ fn not_win32(os: abi::Os) -> bool {
   os != abi::OsWin32
 }
 
-pub fn get_rpath_flags(sess: session::Session, out_filename: &Path) -> Vec<~str> {
+pub fn get_rpath_flags(sess: &Session, out_filename: &Path) -> Vec<~str> {
     let os = sess.targ_cfg.os;
 
     // No rpath on windows
@@ -54,7 +54,7 @@ pub fn get_rpath_flags(sess: session::Session, out_filename: &Path) -> Vec<~str>
     flags
 }
 
-fn get_sysroot_absolute_rt_lib(sess: session::Session) -> Path {
+fn get_sysroot_absolute_rt_lib(sess: &Session) -> Path {
     let r = filesearch::relative_target_lib_path(sess.opts.target_triple);
     let mut p = sess.filesearch.sysroot.join(&r);
     p.push(os::dll_filename("rustrt"));
diff --git a/src/librustc/driver/driver.rs b/src/librustc/driver/driver.rs
index 91425b89ba6..592226a76be 100644
--- a/src/librustc/driver/driver.rs
+++ b/src/librustc/driver/driver.rs
@@ -13,7 +13,7 @@ use back::link;
 use back::{arm, x86, x86_64, mips};
 use driver::session::{Aggressive, CrateTypeExecutable, CrateType,
                       FullDebugInfo, LimitedDebugInfo, NoDebugInfo};
-use driver::session::{Session, Session_, No, Less, Default};
+use driver::session::{Session, No, Less, Default};
 use driver::session;
 use front;
 use lib::llvm::llvm;
@@ -80,7 +80,7 @@ pub fn source_name(input: &Input) -> ~str {
     }
 }
 
-pub fn default_configuration(sess: Session) ->
+pub fn default_configuration(sess: &Session) ->
    ast::CrateConfig {
     let tos = match sess.targ_cfg.os {
         abi::OsWin32 =>   InternedString::new("win32"),
@@ -123,7 +123,7 @@ pub fn append_configuration(cfg: &mut ast::CrateConfig,
     }
 }
 
-pub fn build_configuration(sess: Session) -> ast::CrateConfig {
+pub fn build_configuration(sess: &Session) -> ast::CrateConfig {
     // Combine the configuration requested by the session (command line) with
     // some default and generated configuration items
     let default_cfg = default_configuration(sess);
@@ -170,7 +170,7 @@ impl Input {
     }
 }
 
-pub fn phase_1_parse_input(sess: Session, cfg: ast::CrateConfig, input: &Input)
+pub fn phase_1_parse_input(sess: &Session, cfg: ast::CrateConfig, input: &Input)
     -> ast::Crate {
     let krate = time(sess.time_passes(), "parsing", (), |_| {
         match *input {
@@ -206,7 +206,7 @@ pub fn phase_1_parse_input(sess: Session, cfg: ast::CrateConfig, input: &Input)
 /// syntax expansion, secondary `cfg` expansion, synthesis of a test
 /// harness if one is to be provided and injection of a dependency on the
 /// standard library and prelude.
-pub fn phase_2_configure_and_expand(sess: Session,
+pub fn phase_2_configure_and_expand(sess: &Session,
                                     loader: &mut CrateLoader,
                                     mut krate: ast::Crate,
                                     crate_id: &CrateId)
@@ -214,7 +214,7 @@ pub fn phase_2_configure_and_expand(sess: Session,
     let time_passes = sess.time_passes();
 
     sess.building_library.set(session::building_library(sess.opts, &krate));
-    sess.crate_types.set(session::collect_crate_types(&sess,
+    sess.crate_types.set(session::collect_crate_types(sess,
                                                       krate.attrs
                                                            .as_slice()));
 
@@ -289,12 +289,12 @@ pub fn phase_3_run_analysis_passes(sess: Session,
     let time_passes = sess.time_passes();
 
     time(time_passes, "external crate/lib resolution", (), |_|
-         creader::read_crates(sess, krate,
+         creader::read_crates(&sess, krate,
                               session::sess_os_to_meta_os(sess.targ_cfg.os),
                               token::get_ident_interner()));
 
     let lang_items = time(time_passes, "language item collection", (), |_|
-                          middle::lang_items::collect_language_items(krate, sess));
+                          middle::lang_items::collect_language_items(krate, &sess));
 
     let middle::resolve::CrateMap {
         def_map: def_map,
@@ -304,13 +304,13 @@ pub fn phase_3_run_analysis_passes(sess: Session,
         last_private_map: last_private_map
     } =
         time(time_passes, "resolution", (), |_|
-             middle::resolve::resolve_crate(sess, lang_items, krate));
+             middle::resolve::resolve_crate(&sess, lang_items, krate));
 
     let named_region_map = time(time_passes, "lifetime resolution", (),
-                                |_| middle::resolve_lifetime::krate(sess, krate));
+                                |_| middle::resolve_lifetime::krate(&sess, krate));
 
     time(time_passes, "looking for entry point", (),
-         |_| middle::entry::find_entry_point(sess, krate, &ast_map));
+         |_| middle::entry::find_entry_point(&sess, krate, &ast_map));
 
     sess.macro_registrar_fn.with_mut(|r| *r =
         time(time_passes, "looking for macro registrar", (), |_|
@@ -321,7 +321,7 @@ pub fn phase_3_run_analysis_passes(sess: Session,
                         freevars::annotate_freevars(def_map, krate));
 
     let region_map = time(time_passes, "region resolution", (), |_|
-                          middle::region::resolve_crate(sess, krate));
+                          middle::region::resolve_crate(&sess, krate));
 
     let ty_cx = ty::mk_ctxt(sess, def_map, named_region_map, ast_map,
                             freevars, region_map, lang_items);
@@ -337,8 +337,7 @@ pub fn phase_3_run_analysis_passes(sess: Session,
          middle::const_eval::process_crate(krate, ty_cx));
 
     time(time_passes, "const checking", (), |_|
-         middle::check_const::check_crate(sess, krate, def_map,
-                                          method_map, ty_cx));
+         middle::check_const::check_crate(krate, def_map, method_map, ty_cx));
 
     let maps = (external_exports, last_private_map);
     let (exported_items, public_items) =
@@ -418,17 +417,16 @@ pub struct CrateTranslation {
 
 /// Run the translation phase to LLVM, after which the AST and analysis can
 /// be discarded.
-pub fn phase_4_translate_to_llvm(sess: Session,
-                                 krate: ast::Crate,
+pub fn phase_4_translate_to_llvm(krate: ast::Crate,
                                  analysis: &CrateAnalysis,
                                  outputs: &OutputFilenames) -> CrateTranslation {
-    time(sess.time_passes(), "translation", krate, |krate|
-         trans::base::trans_crate(sess, krate, analysis, outputs))
+    time(analysis.ty_cx.sess.time_passes(), "translation", krate, |krate|
+         trans::base::trans_crate(krate, analysis, outputs))
 }
 
 /// Run LLVM itself, producing a bitcode file, assembly file or object file
 /// as a side effect.
-pub fn phase_5_run_llvm_passes(sess: Session,
+pub fn phase_5_run_llvm_passes(sess: &Session,
                                trans: &CrateTranslation,
                                outputs: &OutputFilenames) {
     if sess.opts.cg.no_integrated_as {
@@ -454,7 +452,7 @@ pub fn phase_5_run_llvm_passes(sess: Session,
 
 /// Run the linker on any artifacts that resulted from the LLVM run.
 /// This should produce either a finished executable or library.
-pub fn phase_6_link_output(sess: Session,
+pub fn phase_6_link_output(sess: &Session,
                            trans: &CrateTranslation,
                            outputs: &OutputFilenames) {
     time(sess.time_passes(), "linking", (), |_|
@@ -464,7 +462,7 @@ pub fn phase_6_link_output(sess: Session,
                            &trans.link.crateid));
 }
 
-pub fn stop_after_phase_3(sess: Session) -> bool {
+pub fn stop_after_phase_3(sess: &Session) -> bool {
    if sess.opts.no_trans {
         debug!("invoked with --no-trans, returning early from compile_input");
         return true;
@@ -472,7 +470,7 @@ pub fn stop_after_phase_3(sess: Session) -> bool {
     return false;
 }
 
-pub fn stop_after_phase_1(sess: Session) -> bool {
+pub fn stop_after_phase_1(sess: &Session) -> bool {
     if sess.opts.parse_only {
         debug!("invoked with --parse-only, returning early from compile_input");
         return true;
@@ -483,7 +481,7 @@ pub fn stop_after_phase_1(sess: Session) -> bool {
     return sess.opts.debugging_opts & session::AST_JSON_NOEXPAND != 0;
 }
 
-pub fn stop_after_phase_2(sess: Session) -> bool {
+pub fn stop_after_phase_2(sess: &Session) -> bool {
     if sess.opts.no_analysis {
         debug!("invoked with --no-analysis, returning early from compile_input");
         return true;
@@ -491,7 +489,7 @@ pub fn stop_after_phase_2(sess: Session) -> bool {
     return sess.opts.debugging_opts & session::AST_JSON != 0;
 }
 
-pub fn stop_after_phase_5(sess: Session) -> bool {
+pub fn stop_after_phase_5(sess: &Session) -> bool {
     if !sess.opts.output_types.iter().any(|&i| i == link::OutputTypeExe) {
         debug!("not building executable, returning early from compile_input");
         return true;
@@ -499,7 +497,7 @@ pub fn stop_after_phase_5(sess: Session) -> bool {
     return false;
 }
 
-fn write_out_deps(sess: Session,
+fn write_out_deps(sess: &Session,
                   input: &Input,
                   outputs: &OutputFilenames,
                   krate: &ast::Crate) -> io::IoResult<()> {
@@ -512,7 +510,7 @@ fn write_out_deps(sess: Session,
             link::OutputTypeExe => {
                 let crate_types = sess.crate_types.borrow();
                 for output in crate_types.get().iter() {
-                    let p = link::filename_for_input(&sess, *output, &id, &file);
+                    let p = link::filename_for_input(sess, *output, &id, &file);
                     out_filenames.push(p);
                 }
             }
@@ -566,33 +564,35 @@ pub fn compile_input(sess: Session, cfg: ast::CrateConfig, input: &Input,
     // We need nested scopes here, because the intermediate results can keep
     // large chunks of memory alive and we want to free them as soon as
     // possible to keep the peak memory usage low
-    let outputs;
-    let trans = {
-        let (expanded_crate, ast_map) = {
-            let krate = phase_1_parse_input(sess, cfg, input);
-            if stop_after_phase_1(sess) { return; }
-            outputs = build_output_filenames(input,
-                                             outdir,
-                                             output,
-                                             krate.attrs.as_slice(),
-                                             sess);
-            let loader = &mut Loader::new(sess);
+    let (outputs, trans, sess) = {
+        let (outputs, expanded_crate, ast_map) = {
+            let krate = phase_1_parse_input(&sess, cfg, input);
+            if stop_after_phase_1(&sess) { return; }
+            let outputs = build_output_filenames(input,
+                                                 outdir,
+                                                 output,
+                                                 krate.attrs.as_slice(),
+                                                 &sess);
+            let loader = &mut Loader::new(&sess);
             let id = link::find_crate_id(krate.attrs.as_slice(),
                                          outputs.out_filestem);
-            phase_2_configure_and_expand(sess, loader, krate, &id)
+            let (expanded_crate, ast_map) = phase_2_configure_and_expand(&sess, loader,
+                                                                         krate, &id);
+            (outputs, expanded_crate, ast_map)
         };
+        write_out_deps(&sess, input, &outputs, &expanded_crate).unwrap();
 
-        write_out_deps(sess, input, &outputs, &expanded_crate).unwrap();
-
-        if stop_after_phase_2(sess) { return; }
+        if stop_after_phase_2(&sess) { return; }
 
         let analysis = phase_3_run_analysis_passes(sess, &expanded_crate, ast_map);
-        if stop_after_phase_3(sess) { return; }
-        phase_4_translate_to_llvm(sess, expanded_crate, &analysis, &outputs)
+        if stop_after_phase_3(&analysis.ty_cx.sess) { return; }
+        let trans = phase_4_translate_to_llvm(expanded_crate,
+                                              &analysis, &outputs);
+        (outputs, trans, analysis.ty_cx.sess)
     };
-    phase_5_run_llvm_passes(sess, &trans, &outputs);
-    if stop_after_phase_5(sess) { return; }
-    phase_6_link_output(sess, &trans, &outputs);
+    phase_5_run_llvm_passes(&sess, &trans, &outputs);
+    if stop_after_phase_5(&sess) { return; }
+    phase_6_link_output(&sess, &trans, &outputs);
 }
 
 struct IdentifiedAnnotation;
@@ -660,19 +660,22 @@ pub fn pretty_print_input(sess: Session,
                           cfg: ast::CrateConfig,
                           input: &Input,
                           ppm: PpMode) {
-    let krate = phase_1_parse_input(sess, cfg, input);
+    let krate = phase_1_parse_input(&sess, cfg, input);
     let id = link::find_crate_id(krate.attrs.as_slice(), input.filestem());
 
     let (krate, ast_map, is_expanded) = match ppm {
         PpmExpanded | PpmExpandedIdentified | PpmTyped => {
-            let loader = &mut Loader::new(sess);
-            let (krate, ast_map) = phase_2_configure_and_expand(sess, loader,
+            let loader = &mut Loader::new(&sess);
+            let (krate, ast_map) = phase_2_configure_and_expand(&sess, loader,
                                                                 krate, &id);
             (krate, Some(ast_map), true)
         }
         _ => (krate, None, false)
     };
 
+    let codemap = sess.codemap;
+    let span_diagnostic = sess.span_diagnostic;
+
     let annotation = match ppm {
         PpmIdentified | PpmExpandedIdentified => {
             ~IdentifiedAnnotation as ~pprust::PpAnn
@@ -687,11 +690,11 @@ pub fn pretty_print_input(sess: Session,
         _ => ~pprust::NoAnn as ~pprust::PpAnn:,
     };
 
-    let src = &sess.codemap.get_filemap(source_name(input)).src;
+    let src = &codemap.get_filemap(source_name(input)).src;
     let mut rdr = MemReader::new(src.as_bytes().to_owned());
     let stdout = io::stdout();
-    pprust::print_crate(sess.codemap,
-                        sess.span_diagnostic,
+    pprust::print_crate(codemap,
+                        span_diagnostic,
                         &krate,
                         source_name(input),
                         &mut rdr,
@@ -1020,7 +1023,7 @@ pub fn build_session_(sopts: @session::Options,
         }
     );
 
-    @Session_ {
+    Session {
         targ_cfg: target_cfg,
         opts: sopts,
         cstore: cstore,
@@ -1043,7 +1046,7 @@ pub fn build_session_(sopts: @session::Options,
     }
 }
 
-pub fn parse_pretty(sess: Session, name: &str) -> PpMode {
+pub fn parse_pretty(sess: &Session, name: &str) -> PpMode {
     match name {
       &"normal" => PpmNormal,
       &"expanded" => PpmExpanded,
@@ -1143,7 +1146,7 @@ pub fn build_output_filenames(input: &Input,
                               odir: &Option<Path>,
                               ofile: &Option<Path>,
                               attrs: &[ast::Attribute],
-                              sess: Session)
+                              sess: &Session)
                            -> OutputFilenames {
     match *ofile {
         None => {
@@ -1196,7 +1199,7 @@ pub fn early_error(msg: &str) -> ! {
     fail!(diagnostic::FatalError);
 }
 
-pub fn list_metadata(sess: Session, path: &Path,
+pub fn list_metadata(sess: &Session, path: &Path,
                      out: &mut io::Writer) -> io::IoResult<()> {
     metadata::loader::list_file_metadata(
         session::sess_os_to_meta_os(sess.targ_cfg.os), path, out)
diff --git a/src/librustc/driver/session.rs b/src/librustc/driver/session.rs
index b4e1516074e..76f6999ae75 100644
--- a/src/librustc/driver/session.rs
+++ b/src/librustc/driver/session.rs
@@ -173,7 +173,7 @@ pub enum CrateType {
     CrateTypeStaticlib,
 }
 
-pub struct Session_ {
+pub struct Session {
     targ_cfg: @Config,
     opts: @Options,
     cstore: @metadata::cstore::CStore,
@@ -201,9 +201,7 @@ pub struct Session_ {
     recursion_limit: Cell<uint>,
 }
 
-pub type Session = @Session_;
-
-impl Session_ {
+impl Session {
     pub fn span_fatal(&self, sp: Span, msg: &str) -> ! {
         self.span_diagnostic.span_fatal(sp, msg)
     }
@@ -451,7 +449,7 @@ cgoptions!(
 )
 
 // Seems out of place, but it uses session, so I'm putting it here
-pub fn expect<T:Clone>(sess: Session, opt: Option<T>, msg: || -> ~str) -> T {
+pub fn expect<T:Clone>(sess: &Session, opt: Option<T>, msg: || -> ~str) -> T {
     diagnostic::expect(sess.diagnostic(), opt, msg)
 }
 
diff --git a/src/librustc/front/assign_node_ids_and_map.rs b/src/librustc/front/assign_node_ids_and_map.rs
index 750d09c2d17..f7c919131a8 100644
--- a/src/librustc/front/assign_node_ids_and_map.rs
+++ b/src/librustc/front/assign_node_ids_and_map.rs
@@ -13,17 +13,17 @@ use driver::session::Session;
 use syntax::ast;
 use syntax::ast_map;
 
-struct NodeIdAssigner {
-    sess: Session
+struct NodeIdAssigner<'a> {
+    sess: &'a Session
 }
 
-impl ast_map::FoldOps for NodeIdAssigner {
+impl<'a> ast_map::FoldOps for NodeIdAssigner<'a> {
     fn new_id(&self, old_id: ast::NodeId) -> ast::NodeId {
         assert_eq!(old_id, ast::DUMMY_NODE_ID);
         self.sess.next_node_id()
     }
 }
 
-pub fn assign_node_ids_and_map(sess: Session, krate: ast::Crate) -> (ast::Crate, ast_map::Map) {
+pub fn assign_node_ids_and_map(sess: &Session, krate: ast::Crate) -> (ast::Crate, ast_map::Map) {
     ast_map::map_crate(krate, NodeIdAssigner { sess: sess })
 }
diff --git a/src/librustc/front/feature_gate.rs b/src/librustc/front/feature_gate.rs
index 36f6cedb4f1..99de2060eee 100644
--- a/src/librustc/front/feature_gate.rs
+++ b/src/librustc/front/feature_gate.rs
@@ -86,12 +86,12 @@ impl Features {
     }
 }
 
-struct Context {
-    features: Vec<&'static str> ,
-    sess: Session,
+struct Context<'a> {
+    features: Vec<&'static str>,
+    sess: &'a Session,
 }
 
-impl Context {
+impl<'a> Context<'a> {
     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
         if !self.has_feature(feature) {
             self.sess.span_err(span, explain);
@@ -114,7 +114,7 @@ impl Context {
     }
 }
 
-impl Visitor<()> for Context {
+impl<'a> Visitor<()> for Context<'a> {
     fn visit_ident(&mut self, sp: Span, id: ast::Ident, _: ()) {
         if !token::get_ident(id).get().is_ascii() {
             self.gate_feature("non_ascii_idents", sp,
@@ -293,7 +293,7 @@ impl Visitor<()> for Context {
     }
 }
 
-pub fn check_crate(sess: Session, krate: &ast::Crate) {
+pub fn check_crate(sess: &Session, krate: &ast::Crate) {
     let mut cx = Context {
         features: Vec::new(),
         sess: sess,
diff --git a/src/librustc/front/show_span.rs b/src/librustc/front/show_span.rs
index aa6fa321a31..36db4e422c1 100644
--- a/src/librustc/front/show_span.rs
+++ b/src/librustc/front/show_span.rs
@@ -19,18 +19,18 @@ use syntax::visit::Visitor;
 
 use driver::session::Session;
 
-struct ShowSpanVisitor {
-    sess: Session
+struct ShowSpanVisitor<'a> {
+    sess: &'a Session
 }
 
-impl Visitor<()> for ShowSpanVisitor {
+impl<'a> Visitor<()> for ShowSpanVisitor<'a> {
     fn visit_expr(&mut self, e: &ast::Expr, _: ()) {
         self.sess.span_note(e.span, "expression");
         visit::walk_expr(self, e, ());
     }
 }
 
-pub fn run(sess: Session, krate: &ast::Crate) {
+pub fn run(sess: &Session, krate: &ast::Crate) {
     let mut v = ShowSpanVisitor { sess: sess };
     visit::walk_crate(&mut v, krate, ());
 }
diff --git a/src/librustc/front/std_inject.rs b/src/librustc/front/std_inject.rs
index c1fd83cab54..40747646167 100644
--- a/src/librustc/front/std_inject.rs
+++ b/src/librustc/front/std_inject.rs
@@ -26,7 +26,7 @@ use syntax::util::small_vector::SmallVector;
 
 pub static VERSION: &'static str = "0.10-pre";
 
-pub fn maybe_inject_crates_ref(sess: Session, krate: ast::Crate)
+pub fn maybe_inject_crates_ref(sess: &Session, krate: ast::Crate)
                                -> ast::Crate {
     if use_std(&krate) {
         inject_crates_ref(sess, krate)
@@ -35,7 +35,7 @@ pub fn maybe_inject_crates_ref(sess: Session, krate: ast::Crate)
     }
 }
 
-pub fn maybe_inject_prelude(sess: Session, krate: ast::Crate) -> ast::Crate {
+pub fn maybe_inject_prelude(sess: &Session, krate: ast::Crate) -> ast::Crate {
     if use_std(&krate) {
         inject_prelude(sess, krate)
     } else {
@@ -55,8 +55,8 @@ fn no_prelude(attrs: &[ast::Attribute]) -> bool {
     attr::contains_name(attrs, "no_implicit_prelude")
 }
 
-struct StandardLibraryInjector {
-    sess: Session,
+struct StandardLibraryInjector<'a> {
+    sess: &'a Session,
 }
 
 pub fn with_version(krate: &str) -> Option<(InternedString, ast::StrStyle)> {
@@ -71,7 +71,7 @@ pub fn with_version(krate: &str) -> Option<(InternedString, ast::StrStyle)> {
     }
 }
 
-impl fold::Folder for StandardLibraryInjector {
+impl<'a> fold::Folder for StandardLibraryInjector<'a> {
     fn fold_crate(&mut self, krate: ast::Crate) -> ast::Crate {
         let mut vis = vec!(ast::ViewItem {
             node: ast::ViewItemExternCrate(token::str_to_ident("std"),
@@ -120,19 +120,19 @@ impl fold::Folder for StandardLibraryInjector {
     }
 }
 
-fn inject_crates_ref(sess: Session, krate: ast::Crate) -> ast::Crate {
+fn inject_crates_ref(sess: &Session, krate: ast::Crate) -> ast::Crate {
     let mut fold = StandardLibraryInjector {
         sess: sess,
     };
     fold.fold_crate(krate)
 }
 
-struct PreludeInjector {
-    sess: Session,
+struct PreludeInjector<'a> {
+    sess: &'a Session,
 }
 
 
-impl fold::Folder for PreludeInjector {
+impl<'a> fold::Folder for PreludeInjector<'a> {
     fn fold_crate(&mut self, krate: ast::Crate) -> ast::Crate {
         if !no_prelude(krate.attrs.as_slice()) {
             // only add `use std::prelude::*;` if there wasn't a
@@ -193,7 +193,7 @@ impl fold::Folder for PreludeInjector {
     }
 }
 
-fn inject_prelude(sess: Session, krate: ast::Crate) -> ast::Crate {
+fn inject_prelude(sess: &Session, krate: ast::Crate) -> ast::Crate {
     let mut fold = PreludeInjector {
         sess: sess,
     };
diff --git a/src/librustc/front/test.rs b/src/librustc/front/test.rs
index 11556322ef1..d79bdeb7884 100644
--- a/src/librustc/front/test.rs
+++ b/src/librustc/front/test.rs
@@ -13,7 +13,7 @@
 #[allow(dead_code)];
 #[allow(unused_imports)];
 
-use driver::session;
+use driver::session::Session;
 use front::config;
 use front::std_inject::with_version;
 use metadata::creader::Loader;
@@ -47,8 +47,8 @@ struct Test {
 }
 
 struct TestCtxt<'a> {
-    sess: session::Session,
-    path: RefCell<Vec<ast::Ident> >,
+    sess: &'a Session,
+    path: RefCell<Vec<ast::Ident>>,
     ext_cx: ExtCtxt<'a>,
     testfns: RefCell<Vec<Test> >,
     is_test_crate: bool,
@@ -57,7 +57,7 @@ struct TestCtxt<'a> {
 
 // Traverse the crate, collecting all the test functions, eliding any
 // existing main functions, and synthesizing a main test harness
-pub fn modify_for_testing(sess: session::Session,
+pub fn modify_for_testing(sess: &Session,
                           krate: ast::Crate) -> ast::Crate {
     // We generate the test harness when building in the 'test'
     // configuration, either with the '--test' or '--cfg test'
@@ -161,7 +161,7 @@ impl<'a> fold::Folder for TestHarnessGenerator<'a> {
     }
 }
 
-fn generate_test_harness(sess: session::Session, krate: ast::Crate)
+fn generate_test_harness(sess: &Session, krate: ast::Crate)
                          -> ast::Crate {
     let loader = &mut Loader::new(sess);
     let mut cx: TestCtxt = TestCtxt {
diff --git a/src/librustc/lib.rs b/src/librustc/lib.rs
index 00cde129d1e..8e8aee55648 100644
--- a/src/librustc/lib.rs
+++ b/src/librustc/lib.rs
@@ -290,9 +290,9 @@ pub fn run_compiler(args: &[~str]) {
     let sess = d::build_session(sopts, input_file_path);
     let odir = matches.opt_str("out-dir").map(|o| Path::new(o));
     let ofile = matches.opt_str("o").map(|o| Path::new(o));
-    let cfg = d::build_configuration(sess);
+    let cfg = d::build_configuration(&sess);
     let pretty = matches.opt_default("pretty", "normal").map(|a| {
-        d::parse_pretty(sess, a)
+        d::parse_pretty(&sess, a)
     });
     match pretty {
       Some::<d::PpMode>(ppm) => {
@@ -306,7 +306,7 @@ pub fn run_compiler(args: &[~str]) {
         match input {
           d::FileInput(ref ifile) => {
             let mut stdout = io::stdout();
-            d::list_metadata(sess, &(*ifile), &mut stdout).unwrap();
+            d::list_metadata(&sess, &(*ifile), &mut stdout).unwrap();
           }
           d::StrInput(_) => {
             d::early_error("can not list metadata for stdin");
@@ -317,9 +317,9 @@ pub fn run_compiler(args: &[~str]) {
     let (crate_id, crate_name, crate_file_name) = sopts.print_metas;
     // these nasty nested conditions are to avoid doing extra work
     if crate_id || crate_name || crate_file_name {
-        let attrs = parse_crate_attrs(sess, &input);
+        let attrs = parse_crate_attrs(&sess, &input);
         let t_outputs = d::build_output_filenames(&input, &odir, &ofile,
-                                                  attrs.as_slice(), sess);
+                                                  attrs.as_slice(), &sess);
         let id = link::find_crate_id(attrs.as_slice(), t_outputs.out_filestem);
 
         if crate_id {
@@ -344,7 +344,7 @@ pub fn run_compiler(args: &[~str]) {
     d::compile_input(sess, cfg, &input, &odir, &ofile);
 }
 
-fn parse_crate_attrs(sess: session::Session, input: &d::Input) ->
+fn parse_crate_attrs(sess: &session::Session, input: &d::Input) ->
                      Vec<ast::Attribute> {
     let result = match *input {
         d::FileInput(ref ifile) => {
diff --git a/src/librustc/metadata/creader.rs b/src/librustc/metadata/creader.rs
index 7769d53865a..5c81b622704 100644
--- a/src/librustc/metadata/creader.rs
+++ b/src/librustc/metadata/creader.rs
@@ -39,7 +39,7 @@ use syntax::visit;
 
 // Traverses an AST, reading all the information about use'd crates and extern
 // libraries necessary for later resolving, typechecking, linking, etc.
-pub fn read_crates(sess: Session,
+pub fn read_crates(sess: &Session,
                    krate: &ast::Crate,
                    os: loader::Os,
                    intr: @IdentInterner) {
@@ -51,12 +51,7 @@ pub fn read_crates(sess: Session,
         intr: intr
     };
     visit_crate(&e, krate);
-    {
-        let mut v = ReadCrateVisitor {
-            e: &mut e
-        };
-        visit::walk_crate(&mut v, krate, ());
-    }
+    visit::walk_crate(&mut e, krate, ());
     let crate_cache = e.crate_cache.borrow();
     dump_crates(crate_cache.get().as_slice());
     warn_if_multiple_versions(&mut e,
@@ -64,17 +59,13 @@ pub fn read_crates(sess: Session,
                               crate_cache.get().as_slice());
 }
 
-struct ReadCrateVisitor<'a> {
-    e: &'a mut Env,
-}
-
-impl<'a> visit::Visitor<()> for ReadCrateVisitor<'a> {
+impl<'a> visit::Visitor<()> for Env<'a> {
     fn visit_view_item(&mut self, a: &ast::ViewItem, _: ()) {
-        visit_view_item(self.e, a);
+        visit_view_item(self, a);
         visit::walk_view_item(self, a, ());
     }
     fn visit_item(&mut self, a: &ast::Item, _: ()) {
-        visit_item(self.e, a);
+        visit_item(self, a);
         visit::walk_item(self, a, ());
     }
 }
@@ -120,8 +111,8 @@ fn warn_if_multiple_versions(e: &mut Env,
     }
 }
 
-struct Env {
-    sess: Session,
+struct Env<'a> {
+    sess: &'a Session,
     os: loader::Os,
     crate_cache: @RefCell<Vec<cache_entry>>,
     next_crate_num: ast::CrateNum,
@@ -391,12 +382,12 @@ fn resolve_crate_deps(e: &mut Env,
     return @RefCell::new(cnum_map);
 }
 
-pub struct Loader {
-    priv env: Env,
+pub struct Loader<'a> {
+    priv env: Env<'a>,
 }
 
-impl Loader {
-    pub fn new(sess: Session) -> Loader {
+impl<'a> Loader<'a> {
+    pub fn new(sess: &'a Session) -> Loader<'a> {
         let os = driver::get_os(driver::host_triple()).unwrap();
         let os = session::sess_os_to_meta_os(os);
         Loader {
@@ -411,7 +402,7 @@ impl Loader {
     }
 }
 
-impl CrateLoader for Loader {
+impl<'a> CrateLoader for Loader<'a> {
     fn load_crate(&mut self, krate: &ast::ViewItem) -> MacroCrate {
         let info = extract_crate_info(&self.env, krate).unwrap();
         let cnum = resolve_crate(&mut self.env, None, info.ident,
diff --git a/src/librustc/metadata/loader.rs b/src/librustc/metadata/loader.rs
index 3a0f7edfb5d..e26759e2b3b 100644
--- a/src/librustc/metadata/loader.rs
+++ b/src/librustc/metadata/loader.rs
@@ -46,7 +46,7 @@ pub enum Os {
 }
 
 pub struct Context<'a> {
-    sess: Session,
+    sess: &'a Session,
     span: Span,
     ident: &'a str,
     crate_id: &'a CrateId,
diff --git a/src/librustc/middle/astencode.rs b/src/librustc/middle/astencode.rs
index fed35922a90..3ab44789838 100644
--- a/src/librustc/middle/astencode.rs
+++ b/src/librustc/middle/astencode.rs
@@ -137,7 +137,7 @@ pub fn decode_inlined_item(cdata: @cstore::crate_metadata,
         });
         let mut ast_dsr = reader::Decoder(ast_doc);
         let from_id_range = Decodable::decode(&mut ast_dsr);
-        let to_id_range = reserve_id_range(dcx.tcx.sess, from_id_range);
+        let to_id_range = reserve_id_range(&dcx.tcx.sess, from_id_range);
         let xcx = @ExtendedDecodeContext {
             dcx: dcx,
             from_id_range: from_id_range,
@@ -154,7 +154,7 @@ pub fn decode_inlined_item(cdata: @cstore::crate_metadata,
         debug!("< Decoded inlined fn: {}::{}",
                path_as_str.unwrap(),
                token::get_ident(ident));
-        region::resolve_inlined_item(tcx.sess, &tcx.region_maps, &ii);
+        region::resolve_inlined_item(&tcx.sess, &tcx.region_maps, &ii);
         decode_side_tables(xcx, ast_doc);
         match ii {
           ast::IIItem(i) => {
@@ -178,7 +178,7 @@ pub fn decode_exported_macro(par_doc: ebml::Doc) -> @ast::Item {
 // ______________________________________________________________________
 // Enumerating the IDs which appear in an AST
 
-fn reserve_id_range(sess: Session,
+fn reserve_id_range(sess: &Session,
                     from_id_range: ast_util::IdRange) -> ast_util::IdRange {
     // Handle the case of an empty range:
     if from_id_range.empty() { return from_id_range; }
diff --git a/src/librustc/middle/check_const.rs b/src/librustc/middle/check_const.rs
index 6841e09f7f2..70d440e49e0 100644
--- a/src/librustc/middle/check_const.rs
+++ b/src/librustc/middle/check_const.rs
@@ -22,7 +22,6 @@ use syntax::visit::Visitor;
 use syntax::visit;
 
 pub struct CheckCrateVisitor {
-    sess: Session,
     def_map: resolve::DefMap,
     method_map: typeck::MethodMap,
     tcx: ty::ctxt,
@@ -30,41 +29,34 @@ pub struct CheckCrateVisitor {
 
 impl Visitor<bool> for CheckCrateVisitor {
     fn visit_item(&mut self, i: &Item, env: bool) {
-        check_item(self, self.sess, self.def_map, i, env);
+        check_item(self, i, env);
     }
     fn visit_pat(&mut self, p: &Pat, env: bool) {
         check_pat(self, p, env);
     }
     fn visit_expr(&mut self, ex: &Expr, env: bool) {
-        check_expr(self, self.sess, self.def_map, self.method_map,
-                   self.tcx, ex, env);
+        check_expr(self, ex, env);
     }
 }
 
-pub fn check_crate(sess: Session,
-                   krate: &Crate,
+pub fn check_crate(krate: &Crate,
                    def_map: resolve::DefMap,
                    method_map: typeck::MethodMap,
                    tcx: ty::ctxt) {
     let mut v = CheckCrateVisitor {
-        sess: sess,
         def_map: def_map,
         method_map: method_map,
         tcx: tcx,
     };
     visit::walk_crate(&mut v, krate, false);
-    sess.abort_if_errors();
+    tcx.sess.abort_if_errors();
 }
 
-pub fn check_item(v: &mut CheckCrateVisitor,
-                  sess: Session,
-                  def_map: resolve::DefMap,
-                  it: &Item,
-                  _is_const: bool) {
+fn check_item(v: &mut CheckCrateVisitor, it: &Item, _is_const: bool) {
     match it.node {
         ItemStatic(_, _, ex) => {
             v.visit_expr(ex, true);
-            check_item_recursion(sess, &v.tcx.map, def_map, it);
+            check_item_recursion(&v.tcx.sess, &v.tcx.map, v.def_map, it);
         }
         ItemEnum(ref enum_definition, _) => {
             for var in (*enum_definition).variants.iter() {
@@ -77,8 +69,8 @@ pub fn check_item(v: &mut CheckCrateVisitor,
     }
 }
 
-pub fn check_pat(v: &mut CheckCrateVisitor, p: &Pat, _is_const: bool) {
-    fn is_str(e: @Expr) -> bool {
+fn check_pat(v: &mut CheckCrateVisitor, p: &Pat, _is_const: bool) {
+    fn is_str(e: &Expr) -> bool {
         match e.node {
             ExprVstore(expr, ExprVstoreUniq) => {
                 match expr.node {
@@ -100,36 +92,30 @@ pub fn check_pat(v: &mut CheckCrateVisitor, p: &Pat, _is_const: bool) {
     }
 }
 
-pub fn check_expr(v: &mut CheckCrateVisitor,
-                  sess: Session,
-                  def_map: resolve::DefMap,
-                  method_map: typeck::MethodMap,
-                  tcx: ty::ctxt,
-                  e: &Expr,
-                  is_const: bool) {
+fn check_expr(v: &mut CheckCrateVisitor, e: &Expr, is_const: bool) {
     if is_const {
         match e.node {
           ExprUnary(UnDeref, _) => { }
           ExprUnary(UnBox, _) | ExprUnary(UnUniq, _) => {
-            sess.span_err(e.span,
-                          "cannot do allocations in constant expressions");
+            v.tcx.sess.span_err(e.span,
+                                "cannot do allocations in constant expressions");
             return;
           }
           ExprLit(lit) if ast_util::lit_is_str(lit) => {}
           ExprBinary(..) | ExprUnary(..) => {
-              let method_call = typeck::MethodCall::expr(e.id);
-            if method_map.borrow().get().contains_key(&method_call) {
-                sess.span_err(e.span, "user-defined operators are not \
-                                       allowed in constant expressions");
+            let method_call = typeck::MethodCall::expr(e.id);
+            if v.method_map.borrow().get().contains_key(&method_call) {
+                v.tcx.sess.span_err(e.span, "user-defined operators are not \
+                                             allowed in constant expressions");
             }
           }
           ExprLit(_) => (),
           ExprCast(_, _) => {
-            let ety = ty::expr_ty(tcx, e);
+            let ety = ty::expr_ty(v.tcx, e);
             if !ty::type_is_numeric(ety) && !ty::type_is_unsafe_ptr(ety) {
-                sess.span_err(e.span, ~"can not cast to `" +
-                              ppaux::ty_to_str(tcx, ety) +
-                              "` in a constant expression");
+                v.tcx.sess.span_err(e.span, ~"can not cast to `" +
+                                              ppaux::ty_to_str(v.tcx, ety) +
+                                             "` in a constant expression");
             }
           }
           ExprPath(ref pth) => {
@@ -138,12 +124,11 @@ pub fn check_expr(v: &mut CheckCrateVisitor,
             // foo::<bar> in a const. Currently that is only done on
             // a path in trans::callee that only works in block contexts.
             if !pth.segments.iter().all(|segment| segment.types.is_empty()) {
-                sess.span_err(
-                    e.span, "paths in constants may only refer to \
-                             items without type parameters");
+                v.tcx.sess.span_err(e.span,
+                                    "paths in constants may only refer to \
+                                     items without type parameters");
             }
-            let def_map = def_map.borrow();
-            match def_map.get().find(&e.id) {
+            match v.def_map.borrow().get().find(&e.id) {
               Some(&DefStatic(..)) |
               Some(&DefFn(_, _)) |
               Some(&DefVariant(_, _, _)) |
@@ -151,24 +136,21 @@ pub fn check_expr(v: &mut CheckCrateVisitor,
 
               Some(&def) => {
                 debug!("(checking const) found bad def: {:?}", def);
-                sess.span_err(
-                    e.span,
+                v.tcx.sess.span_err(e.span,
                     "paths in constants may only refer to \
                      constants or functions");
               }
               None => {
-                sess.span_bug(e.span, "unbound path in const?!");
+                v.tcx.sess.span_bug(e.span, "unbound path in const?!");
               }
             }
           }
           ExprCall(callee, _) => {
-            let def_map = def_map.borrow();
-            match def_map.get().find(&callee.id) {
+            match v.def_map.borrow().get().find(&callee.id) {
                 Some(&DefStruct(..)) => {}    // OK.
                 Some(&DefVariant(..)) => {}    // OK.
                 _ => {
-                    sess.span_err(
-                        e.span,
+                    v.tcx.sess.span_err(e.span,
                         "function calls in constants are limited to \
                          struct and enum constructors");
                 }
@@ -184,18 +166,17 @@ pub fn check_expr(v: &mut CheckCrateVisitor,
           ExprRepeat(..) |
           ExprStruct(..) => { }
           ExprAddrOf(..) => {
-                sess.span_err(
-                    e.span,
+                v.tcx.sess.span_err(e.span,
                     "references in constants may only refer to \
                      immutable values");
           },
           ExprVstore(_, ExprVstoreUniq) => {
-              sess.span_err(e.span, "cannot allocate vectors in constant expressions")
+              v.tcx.sess.span_err(e.span, "cannot allocate vectors in constant expressions")
           },
 
           _ => {
-            sess.span_err(e.span,
-                          "constant contains unimplemented expression type");
+            v.tcx.sess.span_err(e.span,
+                                "constant contains unimplemented expression type");
             return;
           }
         }
@@ -205,14 +186,14 @@ pub fn check_expr(v: &mut CheckCrateVisitor,
 
 struct CheckItemRecursionVisitor<'a> {
     root_it: &'a Item,
-    sess: Session,
+    sess: &'a Session,
     ast_map: &'a ast_map::Map,
     def_map: resolve::DefMap,
     idstack: Vec<NodeId> }
 
 // Make sure a const item doesn't recursively refer to itself
 // FIXME: Should use the dependency graph when it's available (#1356)
-pub fn check_item_recursion<'a>(sess: Session,
+pub fn check_item_recursion<'a>(sess: &'a Session,
                                 ast_map: &'a ast_map::Map,
                                 def_map: resolve::DefMap,
                                 it: &'a Item) {
diff --git a/src/librustc/middle/entry.rs b/src/librustc/middle/entry.rs
index a4ff72d55f2..88a6f7aa1e2 100644
--- a/src/librustc/middle/entry.rs
+++ b/src/librustc/middle/entry.rs
@@ -21,7 +21,7 @@ use syntax::visit;
 use syntax::visit::Visitor;
 
 struct EntryContext<'a> {
-    session: Session,
+    session: &'a Session,
 
     ast_map: &'a ast_map::Map,
 
@@ -48,7 +48,7 @@ impl<'a> Visitor<()> for EntryContext<'a> {
     }
 }
 
-pub fn find_entry_point(session: Session, krate: &Crate, ast_map: &ast_map::Map) {
+pub fn find_entry_point(session: &Session, krate: &Crate, ast_map: &ast_map::Map) {
     if session.building_library.get() {
         // No need to find a main function
         return;
diff --git a/src/librustc/middle/lang_items.rs b/src/librustc/middle/lang_items.rs
index ccf81840a41..ef1a84fd886 100644
--- a/src/librustc/middle/lang_items.rs
+++ b/src/librustc/middle/lang_items.rs
@@ -103,27 +103,23 @@ impl LanguageItems {
     )*
 }
 
-struct LanguageItemCollector {
+struct LanguageItemCollector<'a> {
     items: LanguageItems,
 
-    session: Session,
+    session: &'a Session,
 
     item_refs: HashMap<&'static str, uint>,
 }
 
-struct LanguageItemVisitor<'a> {
-    this: &'a mut LanguageItemCollector,
-}
-
-impl<'a> Visitor<()> for LanguageItemVisitor<'a> {
+impl<'a> Visitor<()> for LanguageItemCollector<'a> {
     fn visit_item(&mut self, item: &ast::Item, _: ()) {
         match extract(item.attrs.as_slice()) {
             Some(value) => {
-                let item_index = self.this.item_refs.find_equiv(&value).map(|x| *x);
+                let item_index = self.item_refs.find_equiv(&value).map(|x| *x);
 
                 match item_index {
                     Some(item_index) => {
-                        self.this.collect_item(item_index, local_def(item.id))
+                        self.collect_item(item_index, local_def(item.id))
                     }
                     None => {}
                 }
@@ -135,8 +131,8 @@ impl<'a> Visitor<()> for LanguageItemVisitor<'a> {
     }
 }
 
-impl LanguageItemCollector {
-    pub fn new(session: Session) -> LanguageItemCollector {
+impl<'a> LanguageItemCollector<'a> {
+    pub fn new(session: &'a Session) -> LanguageItemCollector<'a> {
         let mut item_refs = HashMap::new();
 
         $( item_refs.insert($name, $variant as uint); )*
@@ -165,8 +161,7 @@ impl LanguageItemCollector {
     }
 
     pub fn collect_local_language_items(&mut self, krate: &ast::Crate) {
-        let mut v = LanguageItemVisitor { this: self };
-        visit::walk_crate(&mut v, krate, ());
+        visit::walk_crate(self, krate, ());
     }
 
     pub fn collect_external_language_items(&mut self) {
@@ -200,7 +195,7 @@ pub fn extract(attrs: &[ast::Attribute]) -> Option<InternedString> {
 }
 
 pub fn collect_language_items(krate: &ast::Crate,
-                              session: Session) -> @LanguageItems {
+                              session: &Session) -> @LanguageItems {
     let mut collector = LanguageItemCollector::new(session);
     collector.collect(krate);
     let LanguageItemCollector { items, .. } = collector;
diff --git a/src/librustc/middle/lint.rs b/src/librustc/middle/lint.rs
index 9a6ea297af0..10e56f90f6e 100644
--- a/src/librustc/middle/lint.rs
+++ b/src/librustc/middle/lint.rs
@@ -530,7 +530,7 @@ impl<'a> Context<'a> {
         // of what we changed so we can roll everything back after invoking the
         // specified closure
         let mut pushed = 0u;
-        each_lint(self.tcx.sess, attrs, |meta, level, lintname| {
+        each_lint(&self.tcx.sess, attrs, |meta, level, lintname| {
             match self.dict.find_equiv(&lintname) {
                 None => {
                     self.span_lint(
@@ -594,7 +594,7 @@ impl<'a> Context<'a> {
 
 // Check that every lint from the list of attributes satisfies `f`.
 // Return true if that's the case. Otherwise return false.
-pub fn each_lint(sess: session::Session,
+pub fn each_lint(sess: &session::Session,
                  attrs: &[ast::Attribute],
                  f: |@ast::MetaItem, level, InternedString| -> bool)
                  -> bool {
diff --git a/src/librustc/middle/region.rs b/src/librustc/middle/region.rs
index 15d228662c7..a19b348b78a 100644
--- a/src/librustc/middle/region.rs
+++ b/src/librustc/middle/region.rs
@@ -92,7 +92,7 @@ pub struct Context {
 }
 
 struct RegionResolutionVisitor<'a> {
-    sess: Session,
+    sess: &'a Session,
 
     // Generated maps:
     region_maps: &'a RegionMaps,
@@ -909,7 +909,7 @@ impl<'a> Visitor<Context> for RegionResolutionVisitor<'a> {
     }
 }
 
-pub fn resolve_crate(sess: Session, krate: &ast::Crate) -> RegionMaps {
+pub fn resolve_crate(sess: &Session, krate: &ast::Crate) -> RegionMaps {
     let maps = RegionMaps {
         scope_map: RefCell::new(NodeMap::new()),
         var_map: RefCell::new(NodeMap::new()),
@@ -928,7 +928,7 @@ pub fn resolve_crate(sess: Session, krate: &ast::Crate) -> RegionMaps {
     return maps;
 }
 
-pub fn resolve_inlined_item(sess: Session,
+pub fn resolve_inlined_item(sess: &Session,
                             region_maps: &RegionMaps,
                             item: &ast::InlinedItem) {
     let cx = Context {parent: None,
diff --git a/src/librustc/middle/resolve.rs b/src/librustc/middle/resolve.rs
index 77e44c137a9..1641623b9cb 100644
--- a/src/librustc/middle/resolve.rs
+++ b/src/librustc/middle/resolve.rs
@@ -153,7 +153,7 @@ enum NameDefinition {
     ImportNameDefinition(Def, LastPrivate) //< The name identifies an import.
 }
 
-impl Visitor<()> for Resolver {
+impl<'a> Visitor<()> for Resolver<'a> {
     fn visit_item(&mut self, item: &Item, _: ()) {
         self.resolve_item(item);
     }
@@ -787,9 +787,9 @@ fn namespace_error_to_str(ns: NamespaceError) -> &'static str {
     }
 }
 
-fn Resolver(session: Session,
-            lang_items: @LanguageItems,
-            crate_span: Span) -> Resolver {
+fn Resolver<'a>(session: &'a Session,
+                lang_items: @LanguageItems,
+                crate_span: Span) -> Resolver<'a> {
     let graph_root = @NameBindings();
 
     graph_root.define_module(NoParentLink,
@@ -802,7 +802,7 @@ fn Resolver(session: Session,
     let current_module = graph_root.get_module();
 
     let this = Resolver {
-        session: @session,
+        session: session,
         lang_items: lang_items,
 
         // The outermost module has def ID 0; this is not reflected in the
@@ -843,8 +843,8 @@ fn Resolver(session: Session,
 }
 
 /// The main resolver class.
-struct Resolver {
-    session: @Session,
+struct Resolver<'a> {
+    session: &'a Session,
     lang_items: @LanguageItems,
 
     graph_root: @NameBindings,
@@ -896,11 +896,11 @@ struct Resolver {
     used_imports: HashSet<(NodeId, Namespace)>,
 }
 
-struct BuildReducedGraphVisitor<'a> {
-    resolver: &'a mut Resolver,
+struct BuildReducedGraphVisitor<'a, 'b> {
+    resolver: &'a mut Resolver<'b>,
 }
 
-impl<'a> Visitor<ReducedGraphParent> for BuildReducedGraphVisitor<'a> {
+impl<'a, 'b> Visitor<ReducedGraphParent> for BuildReducedGraphVisitor<'a, 'b> {
 
     fn visit_item(&mut self, item: &Item, context: ReducedGraphParent) {
         let p = self.resolver.build_reduced_graph_for_item(item, context);
@@ -928,16 +928,16 @@ impl<'a> Visitor<ReducedGraphParent> for BuildReducedGraphVisitor<'a> {
 
 }
 
-struct UnusedImportCheckVisitor<'a> { resolver: &'a mut Resolver }
+struct UnusedImportCheckVisitor<'a, 'b> { resolver: &'a mut Resolver<'b> }
 
-impl<'a> Visitor<()> for UnusedImportCheckVisitor<'a> {
+impl<'a, 'b> Visitor<()> for UnusedImportCheckVisitor<'a, 'b> {
     fn visit_view_item(&mut self, vi: &ViewItem, _: ()) {
         self.resolver.check_for_item_unused_imports(vi);
         visit::walk_view_item(self, vi, ());
     }
 }
 
-impl Resolver {
+impl<'a> Resolver<'a> {
     /// The main name resolution procedure.
     fn resolve(&mut self, krate: &ast::Crate) {
         self.build_reduced_graph(krate);
@@ -5571,7 +5571,7 @@ pub struct CrateMap {
 }
 
 /// Entry point to crate resolution.
-pub fn resolve_crate(session: Session,
+pub fn resolve_crate(session: &Session,
                      lang_items: @LanguageItems,
                      krate: &Crate)
                   -> CrateMap {
diff --git a/src/librustc/middle/resolve_lifetime.rs b/src/librustc/middle/resolve_lifetime.rs
index 88eaf256be8..9790b392d0f 100644
--- a/src/librustc/middle/resolve_lifetime.rs
+++ b/src/librustc/middle/resolve_lifetime.rs
@@ -17,7 +17,7 @@
  * way. Therefore we break lifetime name resolution into a separate pass.
  */
 
-use driver::session;
+use driver::session::Session;
 use std::cell::RefCell;
 use std::vec_ng::Vec;
 use util::nodemap::NodeMap;
@@ -40,8 +40,8 @@ fn lifetime_show(lt_name: &ast::Name) -> token::InternedString {
     token::get_name(*lt_name)
 }
 
-struct LifetimeContext {
-    sess: session::Session,
+struct LifetimeContext<'a> {
+    sess: &'a Session,
     named_region_map: @RefCell<NamedRegionMap>,
 }
 
@@ -60,8 +60,7 @@ enum ScopeChain<'a> {
 
 type Scope<'a> = &'a ScopeChain<'a>;
 
-pub fn krate(sess: session::Session, krate: &ast::Crate)
-             -> @RefCell<NamedRegionMap> {
+pub fn krate(sess: &Session, krate: &ast::Crate) -> @RefCell<NamedRegionMap> {
     let mut ctxt = LifetimeContext {
         sess: sess,
         named_region_map: @RefCell::new(NodeMap::new())
@@ -71,7 +70,7 @@ pub fn krate(sess: session::Session, krate: &ast::Crate)
     ctxt.named_region_map
 }
 
-impl<'a> Visitor<Scope<'a>> for LifetimeContext {
+impl<'a, 'b> Visitor<Scope<'a>> for LifetimeContext<'b> {
     fn visit_item(&mut self,
                   item: &ast::Item,
                   _: Scope<'a>) {
@@ -181,7 +180,7 @@ impl<'a> ScopeChain<'a> {
     }
 }
 
-impl LifetimeContext {
+impl<'a> LifetimeContext<'a> {
     /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
     fn visit_fn_decl(&mut self,
                      n: ast::NodeId,
diff --git a/src/librustc/middle/trans/_match.rs b/src/librustc/middle/trans/_match.rs
index 4f190c5d697..2f5173f9c05 100644
--- a/src/librustc/middle/trans/_match.rs
+++ b/src/librustc/middle/trans/_match.rs
@@ -373,7 +373,7 @@ fn variant_opt(bcx: &Block, pat_id: ast::NodeId) -> Opt {
             return lit(UnitLikeStructLit(pat_id));
         }
         _ => {
-            ccx.sess.bug("non-variant or struct in variant_opt()");
+            ccx.sess().bug("non-variant or struct in variant_opt()");
         }
     }
 }
@@ -1324,8 +1324,7 @@ fn compare_values<'a>(
             }
         }
         _ => {
-            cx.tcx().sess.bug("only scalars and strings supported in \
-                                compare_values");
+            cx.sess().bug("only scalars and strings supported in compare_values");
         }
     }
 }
@@ -1585,7 +1584,7 @@ fn compile_submatch_continue<'r,
         let tup_repr = adt::represent_type(bcx.ccx(), tup_ty);
         let n_tup_elts = match ty::get(tup_ty).sty {
           ty::ty_tup(ref elts) => elts.len(),
-          _ => ccx.sess.bug("non-tuple type in tuple pattern")
+          _ => ccx.sess().bug("non-tuple type in tuple pattern")
         };
         let tup_vals = Vec::from_fn(n_tup_elts, |i| {
             adt::trans_field_ptr(bcx, tup_repr, val, 0, i)
@@ -1612,7 +1611,7 @@ fn compile_submatch_continue<'r,
                     ty::lookup_struct_fields(tcx, struct_id).len();
             }
             _ => {
-                ccx.sess.bug("non-struct type in tuple struct pattern");
+                ccx.sess().bug("non-struct type in tuple struct pattern");
             }
         }
 
@@ -2093,7 +2092,7 @@ pub fn store_arg<'a>(mut bcx: &'a Block<'a>,
             // like `x: T`
             let arg_ty = node_id_type(bcx, pat.id);
             if type_of::arg_is_indirect(bcx.ccx(), arg_ty)
-                && bcx.ccx().sess.opts.debuginfo != FullDebugInfo {
+                && bcx.sess().opts.debuginfo != FullDebugInfo {
                 // Don't copy an indirect argument to an alloca, the caller
                 // already put it in a temporary alloca and gave it up, unless
                 // we emit extra-debug-info, which requires local allocas :(.
@@ -2297,8 +2296,7 @@ fn bind_irrefutable_pat<'a>(
             bcx = bind_irrefutable_pat(bcx, inner, loaded_val, binding_mode, cleanup_scope);
         }
         ast::PatVec(..) => {
-            bcx.tcx().sess.span_bug(
-                pat.span,
+            bcx.sess().span_bug(pat.span,
                 format!("vector patterns are never irrefutable!"));
         }
         ast::PatWild | ast::PatWildMulti | ast::PatLit(_) | ast::PatRange(_, _) => ()
diff --git a/src/librustc/middle/trans/adt.rs b/src/librustc/middle/trans/adt.rs
index 00a93b66ce0..556e78a88f3 100644
--- a/src/librustc/middle/trans/adt.rs
+++ b/src/librustc/middle/trans/adt.rs
@@ -177,9 +177,9 @@ fn represent_type_uncached(cx: &CrateContext, t: ty::t) -> Repr {
             // non-empty body, explicit discriminants should have
             // been rejected by a checker before this point.
             if !cases.iter().enumerate().all(|(i,c)| c.discr == (i as Disr)) {
-                cx.sess.bug(format!("non-C-like enum {} with specified \
-                                  discriminants",
-                                 ty::item_path_str(cx.tcx, def_id)))
+                cx.sess().bug(format!("non-C-like enum {} with specified \
+                                      discriminants",
+                                      ty::item_path_str(cx.tcx, def_id)))
             }
 
             if cases.len() == 1 {
@@ -230,7 +230,7 @@ fn represent_type_uncached(cx: &CrateContext, t: ty::t) -> Repr {
                           false)
             }))
         }
-        _ => cx.sess.bug("adt::represent_type called on non-ADT type")
+        _ => cx.sess().bug("adt::represent_type called on non-ADT type")
     }
 }
 
@@ -324,12 +324,12 @@ fn range_to_inttype(cx: &CrateContext, hint: Hint, bounds: &IntBounds) -> IntTyp
     match hint {
         attr::ReprInt(span, ity) => {
             if !bounds_usable(cx, ity, bounds) {
-                cx.sess.span_bug(span, "representation hint insufficient for discriminant range")
+                cx.sess().span_bug(span, "representation hint insufficient for discriminant range")
             }
             return ity;
         }
         attr::ReprExtern => {
-            attempts = match cx.sess.targ_cfg.arch {
+            attempts = match cx.sess().targ_cfg.arch {
                 X86 | X86_64 => at_least_32,
                 // WARNING: the ARM EABI has two variants; the one corresponding to `at_least_32`
                 // appears to be used on Linux and NetBSD, but some systems may use the variant
@@ -577,7 +577,7 @@ pub fn trans_case<'a>(bcx: &'a Block<'a>, r: &Repr, discr: Disr)
                                                        discr as u64, true)))
         }
         Univariant(..) => {
-            bcx.ccx().sess.bug("no cases for univariants or structs")
+            bcx.ccx().sess().bug("no cases for univariants or structs")
         }
         NullablePointer{ .. } => {
             assert!(discr == 0 || discr == 1);
@@ -651,7 +651,7 @@ pub fn num_args(r: &Repr, discr: Disr) -> uint {
 pub fn deref_ty(ccx: &CrateContext, r: &Repr) -> ty::t {
     match *r {
         CEnum(..) => {
-            ccx.sess.bug("deref of c-like enum")
+            ccx.sess().bug("deref of c-like enum")
         }
         Univariant(ref st, _) => {
             *st.fields.get(0)
@@ -661,7 +661,7 @@ pub fn deref_ty(ccx: &CrateContext, r: &Repr) -> ty::t {
             *cases.get(0).fields.get(0)
         }
         NullablePointer{ .. } => {
-            ccx.sess.bug("deref of nullable ptr")
+            ccx.sess().bug("deref of nullable ptr")
         }
     }
 }
@@ -674,7 +674,7 @@ pub fn trans_field_ptr(bcx: &Block, r: &Repr, val: ValueRef, discr: Disr,
     // someday), it will need to return a possibly-new bcx as well.
     match *r {
         CEnum(..) => {
-            bcx.ccx().sess.bug("element access in C-like enum")
+            bcx.ccx().sess().bug("element access in C-like enum")
         }
         Univariant(ref st, _dtor) => {
             assert_eq!(discr, 0);
@@ -719,7 +719,7 @@ fn struct_field_ptr(bcx: &Block, st: &Struct, val: ValueRef, ix: uint,
 pub fn trans_drop_flag_ptr(bcx: &Block, r: &Repr, val: ValueRef) -> ValueRef {
     match *r {
         Univariant(ref st, true) => GEPi(bcx, val, [0, st.fields.len() - 1]),
-        _ => bcx.ccx().sess.bug("tried to get drop flag of non-droppable type")
+        _ => bcx.ccx().sess().bug("tried to get drop flag of non-droppable type")
     }
 }
 
@@ -874,7 +874,7 @@ pub fn const_get_discrim(ccx: &CrateContext, r: &Repr, val: ValueRef)
 pub fn const_get_field(ccx: &CrateContext, r: &Repr, val: ValueRef,
                        _discr: Disr, ix: uint) -> ValueRef {
     match *r {
-        CEnum(..) => ccx.sess.bug("element access in C-like enum const"),
+        CEnum(..) => ccx.sess().bug("element access in C-like enum const"),
         Univariant(..) => const_struct_field(ccx, val, ix),
         General(..) => const_struct_field(ccx, val, ix + 1),
         NullablePointer{ .. } => const_struct_field(ccx, val, ix)
diff --git a/src/librustc/middle/trans/base.rs b/src/librustc/middle/trans/base.rs
index a2ee57d6df1..46afaccccf9 100644
--- a/src/librustc/middle/trans/base.rs
+++ b/src/librustc/middle/trans/base.rs
@@ -144,7 +144,7 @@ pub struct StatRecorder {
 
 impl StatRecorder {
     pub fn new(ccx: @CrateContext, name: ~str) -> StatRecorder {
-        let start = if ccx.sess.trans_stats() {
+        let start = if ccx.sess().trans_stats() {
             time::precise_time_ns()
         } else {
             0
@@ -162,7 +162,7 @@ impl StatRecorder {
 #[unsafe_destructor]
 impl Drop for StatRecorder {
     fn drop(&mut self) {
-        if self.ccx.sess.trans_stats() {
+        if self.ccx.sess().trans_stats() {
             let end = time::precise_time_ns();
             let elapsed = ((end - self.start) / 1_000_000) as uint;
             let iend = self.ccx.stats.n_llvm_insns.get();
@@ -355,8 +355,8 @@ pub fn malloc_raw_dyn<'a>(
         match li.require(it) {
             Ok(id) => id,
             Err(s) => {
-                bcx.tcx().sess.fatal(format!("allocation of `{}` {}",
-                                          bcx.ty_to_str(t), s));
+                bcx.sess().fatal(format!("allocation of `{}` {}",
+                                         bcx.ty_to_str(t), s));
             }
         }
     }
@@ -522,7 +522,7 @@ pub fn set_no_split_stack(f: ValueRef) {
 pub fn note_unique_llvm_symbol(ccx: &CrateContext, sym: ~str) {
     let mut all_llvm_symbols = ccx.all_llvm_symbols.borrow_mut();
     if all_llvm_symbols.get().contains(&sym) {
-        ccx.sess.bug(~"duplicate LLVM symbol: " + sym);
+        ccx.sess().bug(~"duplicate LLVM symbol: " + sym);
     }
     all_llvm_symbols.get().insert(sym);
 }
@@ -555,7 +555,7 @@ pub fn get_res_dtor(ccx: @CrateContext,
         get_item_val(ccx, did.node)
     } else {
         let tcx = ccx.tcx;
-        let name = csearch::get_symbol(ccx.sess.cstore, did);
+        let name = csearch::get_symbol(ccx.sess().cstore, did);
         let class_ty = ty::subst_tps(tcx,
                                      substs,
                                      None,
@@ -572,7 +572,7 @@ pub fn get_res_dtor(ccx: @CrateContext,
 
 // Structural comparison: a rather involved form of glue.
 pub fn maybe_name_value(cx: &CrateContext, v: ValueRef, s: &str) {
-    if cx.sess.opts.cg.save_temps {
+    if cx.sess().opts.cg.save_temps {
         s.with_c_str(|buf| {
             unsafe {
                 llvm::LLVMSetValueName(v, buf)
@@ -617,8 +617,7 @@ pub fn compare_scalar_values<'a>(
                              -> ValueRef {
     let _icx = push_ctxt("compare_scalar_values");
     fn die(cx: &Block) -> ! {
-        cx.tcx().sess.bug("compare_scalar_values: must be a\
-                           comparison operator");
+        cx.sess().bug("compare_scalar_values: must be a comparison operator");
     }
     match nt {
       nil_type => {
@@ -772,8 +771,8 @@ pub fn iter_structural_ty<'r,
                           _match::single_result(r) => {
                               AddCase(llswitch, r.val, variant_cx.llbb)
                           }
-                          _ => ccx.sess.unimpl("value from adt::trans_case \
-                                                in iter_structural_ty")
+                          _ => ccx.sess().unimpl("value from adt::trans_case \
+                                                  in iter_structural_ty")
                       }
                       let variant_cx =
                           iter_variant(variant_cx,
@@ -786,8 +785,8 @@ pub fn iter_structural_ty<'r,
                   }
                   cx = next_cx;
               }
-              _ => ccx.sess.unimpl("value from adt::trans_switch \
-                                    in iter_structural_ty")
+              _ => ccx.sess().unimpl("value from adt::trans_switch \
+                                      in iter_structural_ty")
           }
       }
       _ => cx.sess().unimpl("type in iter_structural_ty")
@@ -865,8 +864,8 @@ pub fn fail_if_zero<'a>(
         ICmp(cx, lib::llvm::IntEQ, rhs, zero)
       }
       _ => {
-        cx.tcx().sess.bug(~"fail-if-zero on unexpected type: " +
-                          ty_to_str(cx.ccx().tcx, rhs_t));
+        cx.sess().bug(~"fail-if-zero on unexpected type: " +
+                      ty_to_str(cx.ccx().tcx, rhs_t));
       }
     };
     with_cond(cx, is_zero, |bcx| {
@@ -875,11 +874,11 @@ pub fn fail_if_zero<'a>(
 }
 
 pub fn trans_external_path(ccx: &CrateContext, did: ast::DefId, t: ty::t) -> ValueRef {
-    let name = csearch::get_symbol(ccx.sess.cstore, did);
+    let name = csearch::get_symbol(ccx.sess().cstore, did);
     match ty::get(t).sty {
         ty::ty_bare_fn(ref fn_ty) => {
-            match fn_ty.abis.for_target(ccx.sess.targ_cfg.os,
-                                        ccx.sess.targ_cfg.arch) {
+            match fn_ty.abis.for_target(ccx.sess().targ_cfg.os,
+                                        ccx.sess().targ_cfg.arch) {
                 Some(Rust) | Some(RustIntrinsic) => {
                     get_extern_rust_fn(ccx,
                                        fn_ty.sig.inputs.as_slice(),
@@ -970,7 +969,7 @@ pub fn invoke<'a>(
 }
 
 pub fn need_invoke(bcx: &Block) -> bool {
-    if bcx.ccx().sess.no_landing_pads() {
+    if bcx.sess().no_landing_pads() {
         return false;
     }
 
@@ -1081,7 +1080,7 @@ pub fn with_cond<'a>(
 pub fn call_memcpy(cx: &Block, dst: ValueRef, src: ValueRef, n_bytes: ValueRef, align: u32) {
     let _icx = push_ctxt("call_memcpy");
     let ccx = cx.ccx();
-    let key = match ccx.sess.targ_cfg.arch {
+    let key = match ccx.sess().targ_cfg.arch {
         X86 | Arm | Mips => "llvm.memcpy.p0i8.p0i8.i32",
         X86_64 => "llvm.memcpy.p0i8.p0i8.i64"
     };
@@ -1125,7 +1124,7 @@ fn memzero(b: &Builder, llptr: ValueRef, ty: Type) {
     let _icx = push_ctxt("memzero");
     let ccx = b.ccx;
 
-    let intrinsic_key = match ccx.sess.targ_cfg.arch {
+    let intrinsic_key = match ccx.sess().targ_cfg.arch {
         X86 | Arm | Mips => "llvm.memset.p0i8.i32",
         X86_64 => "llvm.memset.p0i8.i64"
     };
@@ -1384,7 +1383,7 @@ fn copy_args_to_allocas<'a>(fcx: &FunctionContext<'a>,
 
         bcx = _match::store_arg(bcx, args[i].pat, arg_datum, arg_scope_id);
 
-        if fcx.ccx.sess.opts.debuginfo == FullDebugInfo {
+        if fcx.ccx.sess().opts.debuginfo == FullDebugInfo {
             debuginfo::create_argument_metadata(bcx, &args[i]);
         }
     }
@@ -1615,7 +1614,7 @@ fn trans_enum_variant_or_tuple_like_struct(ccx: @CrateContext,
 
     let result_ty = match ty::get(ctor_ty).sty {
         ty::ty_bare_fn(ref bft) => bft.sig.output,
-        _ => ccx.sess.bug(
+        _ => ccx.sess().bug(
             format!("trans_enum_variant_or_tuple_like_struct: \
                   unexpected ctor return type {}",
                  ty_to_str(ccx.tcx, ctor_ty)))
@@ -1724,16 +1723,16 @@ pub fn trans_item(ccx: @CrateContext, item: &ast::Item) {
           // because we need to get the value of the bool out of LLVM
           if attr::contains_name(item.attrs.as_slice(), "static_assert") {
               if m == ast::MutMutable {
-                  ccx.sess.span_fatal(expr.span,
-                                      "cannot have static_assert on a mutable \
-                                       static");
+                  ccx.sess().span_fatal(expr.span,
+                                        "cannot have static_assert on a mutable \
+                                         static");
               }
 
               let const_values = ccx.const_values.borrow();
               let v = const_values.get().get_copy(&item.id);
               unsafe {
                   if !(llvm::LLVMConstIntGetZExtValue(v) != 0) {
-                      ccx.sess.span_fatal(expr.span, "static assertion failed");
+                      ccx.sess().span_fatal(expr.span, "static assertion failed");
                   }
               }
           }
@@ -1798,7 +1797,7 @@ fn finish_register_fn(ccx: @CrateContext, sp: Span, sym: ~str, node_id: ast::Nod
         }
     }
 
-    if is_entry_fn(&ccx.sess, node_id) && !ccx.sess.building_library.get() {
+    if is_entry_fn(ccx.sess(), node_id) && !ccx.sess().building_library.get() {
         create_entry_wrapper(ccx, sp, llfn);
     }
 }
@@ -1853,7 +1852,7 @@ pub fn is_entry_fn(sess: &Session, node_id: ast::NodeId) -> bool {
 pub fn create_entry_wrapper(ccx: @CrateContext,
                            _sp: Span,
                            main_llfn: ValueRef) {
-    let et = ccx.sess.entry_type.get().unwrap();
+    let et = ccx.sess().entry_type.get().unwrap();
     match et {
         session::EntryMain => {
             create_entry_fn(ccx, main_llfn, true);
@@ -1881,7 +1880,7 @@ pub fn create_entry_wrapper(ccx: @CrateContext,
             let (start_fn, args) = if use_start_lang_item {
                 let start_def_id = match ccx.tcx.lang_items.require(StartFnLangItem) {
                     Ok(id) => id,
-                    Err(s) => { ccx.tcx.sess.fatal(s); }
+                    Err(s) => { ccx.sess().fatal(s); }
                 };
                 let start_fn = if start_def_id.krate == ast::LOCAL_CRATE {
                     get_item_val(ccx, start_def_id.node)
@@ -1973,7 +1972,7 @@ pub fn get_item_val(ccx: @CrateContext, id: ast::NodeId) -> ValueRef {
                                 match external_srcs.get().find(&i.id) {
                                     Some(&did) => {
                                         debug!("but found in other crate...");
-                                        (csearch::get_symbol(ccx.sess.cstore,
+                                        (csearch::get_symbol(ccx.sess().cstore,
                                                              did), false)
                                     }
                                     None => (sym, true)
@@ -2013,7 +2012,7 @@ pub fn get_item_val(ccx: @CrateContext, id: ast::NodeId) -> ValueRef {
                                         let reachable =
                                             ccx.reachable.borrow();
                                         if reachable.get().contains(&id) {
-                                            ccx.sess.span_bug(i.span,
+                                            ccx.sess().span_bug(i.span,
                                                 "insignificant static is \
                                                  reachable");
                                         }
@@ -2093,8 +2092,8 @@ pub fn get_item_val(ccx: @CrateContext, id: ast::NodeId) -> ValueRef {
                     debug!("get_item_val(): processing a NodeTraitMethod");
                     match *trait_method {
                         ast::Required(_) => {
-                            ccx.sess.bug("unexpected variant: required trait method in \
-                                         get_item_val()");
+                            ccx.sess().bug("unexpected variant: required trait method in \
+                                           get_item_val()");
                         }
                         ast::Provided(m) => {
                             register_method(ccx, id, m)
@@ -2152,8 +2151,8 @@ pub fn get_item_val(ccx: @CrateContext, id: ast::NodeId) -> ValueRef {
                     // Only register the constructor if this is a tuple-like struct.
                     match struct_def.ctor_id {
                         None => {
-                            ccx.tcx.sess.bug("attempt to register a constructor of \
-                                              a non-tuple-like struct")
+                            ccx.sess().bug("attempt to register a constructor of \
+                                            a non-tuple-like struct")
                         }
                         Some(ctor_id) => {
                             let parent = ccx.tcx.map.get_parent(id);
@@ -2173,8 +2172,8 @@ pub fn get_item_val(ccx: @CrateContext, id: ast::NodeId) -> ValueRef {
                 }
 
                 ref variant => {
-                    ccx.sess.bug(format!("get_item_val(): unexpected variant: {:?}",
-                                 variant))
+                    ccx.sess().bug(format!("get_item_val(): unexpected variant: {:?}",
+                                   variant))
                 }
             };
 
@@ -2409,7 +2408,7 @@ pub fn symname(name: &str, hash: &str, vers: &str) -> ~str {
     link::exported_name(ast_map::Values(path.iter()).chain(None), hash, vers)
 }
 
-pub fn decl_crate_map(sess: session::Session, mapmeta: LinkMeta,
+pub fn decl_crate_map(sess: &Session, mapmeta: LinkMeta,
                       llmod: ModuleRef) -> (~str, ValueRef) {
     let targ_cfg = sess.targ_cfg;
     let int_type = Type::int(targ_cfg.arch);
@@ -2452,7 +2451,7 @@ pub fn fill_crate_map(ccx: @CrateContext, map: ValueRef) {
                 llvm::LLVMConstPointerCast(get_item_val(ccx, did.node),
                                            ccx.int_type.ptr_to().to_ref())
             } else {
-                let name = csearch::get_symbol(ccx.sess.cstore, did);
+                let name = csearch::get_symbol(ccx.sess().cstore, did);
                 let global = name.with_c_str(|buf| {
                     llvm::LLVMAddGlobal(ccx.llmod, ccx.int_type.to_ref(), buf)
                 });
@@ -2472,7 +2471,7 @@ pub fn fill_crate_map(ccx: @CrateContext, map: ValueRef) {
 pub fn crate_ctxt_to_encode_parms<'r>(cx: &'r CrateContext, ie: encoder::EncodeInlinedItem<'r>)
     -> encoder::EncodeParams<'r> {
 
-        let diag = cx.sess.diagnostic();
+        let diag = cx.sess().diagnostic();
         let item_symbols = &cx.item_symbols;
         let link_meta = &cx.link_meta;
         encoder::EncodeParams {
@@ -2482,7 +2481,7 @@ pub fn crate_ctxt_to_encode_parms<'r>(cx: &'r CrateContext, ie: encoder::EncodeI
             item_symbols: item_symbols,
             non_inlineable_statics: &cx.non_inlineable_statics,
             link_meta: link_meta,
-            cstore: cx.sess.cstore,
+            cstore: cx.sess().cstore,
             encode_inlined_item: ie,
         }
 }
@@ -2490,7 +2489,7 @@ pub fn crate_ctxt_to_encode_parms<'r>(cx: &'r CrateContext, ie: encoder::EncodeI
 pub fn write_metadata(cx: &CrateContext, krate: &ast::Crate) -> Vec<u8> {
     use flate;
 
-    if !cx.sess.building_library.get() {
+    if !cx.sess().building_library.get() {
         return Vec::new()
     }
 
@@ -2512,15 +2511,14 @@ pub fn write_metadata(cx: &CrateContext, krate: &ast::Crate) -> Vec<u8> {
     });
     unsafe {
         llvm::LLVMSetInitializer(llglobal, llconst);
-        cx.sess.targ_cfg.target_strs.meta_sect_name.with_c_str(|buf| {
+        cx.sess().targ_cfg.target_strs.meta_sect_name.with_c_str(|buf| {
             llvm::LLVMSetSection(llglobal, buf)
         });
     }
     return metadata;
 }
 
-pub fn trans_crate(sess: session::Session,
-                   krate: ast::Crate,
+pub fn trans_crate(krate: ast::Crate,
                    analysis: &CrateAnalysis,
                    output: &OutputFilenames) -> CrateTranslation {
     // Before we touch LLVM, make sure that multithreading is enabled.
@@ -2537,7 +2535,7 @@ pub fn trans_crate(sess: session::Session,
         });
 
         if POISONED {
-            sess.bug("couldn't enable multi-threaded LLVM");
+            analysis.ty_cx.sess.bug("couldn't enable multi-threaded LLVM");
         }
     }
 
@@ -2553,8 +2551,7 @@ pub fn trans_crate(sess: session::Session,
     // 1. http://llvm.org/bugs/show_bug.cgi?id=11479
     let llmod_id = link_meta.crateid.name + ".rs";
 
-    let ccx = @CrateContext::new(sess,
-                                 llmod_id,
+    let ccx = @CrateContext::new(llmod_id,
                                  analysis.ty_cx,
                                  analysis.exp_map2,
                                  analysis.maps,
@@ -2574,7 +2571,7 @@ pub fn trans_crate(sess: session::Session,
     // __rust_crate_map_toplevel symbol (extra underscore) which it will
     // subsequently fail to find. So to mitigate that we just introduce
     // an alias from the symbol it expects to the one that actually exists.
-    if ccx.sess.targ_cfg.os == OsWin32 && !ccx.sess.building_library.get() {
+    if ccx.sess().targ_cfg.os == OsWin32 && !ccx.sess().building_library.get() {
 
         let maptype = val_ty(ccx.crate_map).to_ref();
 
@@ -2587,13 +2584,13 @@ pub fn trans_crate(sess: session::Session,
     }
 
     glue::emit_tydescs(ccx);
-    if ccx.sess.opts.debuginfo != NoDebugInfo {
+    if ccx.sess().opts.debuginfo != NoDebugInfo {
         debuginfo::finalize(ccx);
     }
 
     // Translate the metadata.
     let metadata = write_metadata(ccx, &krate);
-    if ccx.sess.trans_stats() {
+    if ccx.sess().trans_stats() {
         println!("--- trans stats ---");
         println!("n_static_tydescs: {}", ccx.stats.n_static_tydescs.get());
         println!("n_glues_created: {}", ccx.stats.n_glues_created.get());
@@ -2619,7 +2616,7 @@ pub fn trans_crate(sess: session::Session,
             }
         }
     }
-    if ccx.sess.count_llvm_insns() {
+    if ccx.sess().count_llvm_insns() {
         let llvm_insns = ccx.stats.llvm_insns.borrow();
         for (k, v) in llvm_insns.get().iter() {
             println!("{:7u} {}", *v, *k);
diff --git a/src/librustc/middle/trans/builder.rs b/src/librustc/middle/trans/builder.rs
index 15e74b1b55d..dd34a034d0e 100644
--- a/src/librustc/middle/trans/builder.rs
+++ b/src/librustc/middle/trans/builder.rs
@@ -44,13 +44,13 @@ impl<'a> Builder<'a> {
     }
 
     pub fn count_insn(&self, category: &str) {
-        if self.ccx.sess.trans_stats() {
+        if self.ccx.sess().trans_stats() {
             self.ccx.stats.n_llvm_insns.set(self.ccx
                                                 .stats
                                                 .n_llvm_insns
                                                 .get() + 1);
         }
-        if self.ccx.sess.count_llvm_insns() {
+        if self.ccx.sess().count_llvm_insns() {
             base::with_insn_ctxt(|v| {
                 let mut h = self.ccx.stats.llvm_insns.borrow_mut();
 
@@ -748,15 +748,15 @@ impl<'a> Builder<'a> {
     }
 
     pub fn add_span_comment(&self, sp: Span, text: &str) {
-        if self.ccx.sess.asm_comments() {
-            let s = format!("{} ({})", text, self.ccx.sess.codemap.span_to_str(sp));
+        if self.ccx.sess().asm_comments() {
+            let s = format!("{} ({})", text, self.ccx.sess().codemap.span_to_str(sp));
             debug!("{}", s);
             self.add_comment(s);
         }
     }
 
     pub fn add_comment(&self, text: &str) {
-        if self.ccx.sess.asm_comments() {
+        if self.ccx.sess().asm_comments() {
             let sanitized = text.replace("$", "");
             let comment_text = format!("\\# {}", sanitized.replace("\n", "\n\t# "));
             self.count_insn("inlineasm");
diff --git a/src/librustc/middle/trans/cabi.rs b/src/librustc/middle/trans/cabi.rs
index b8ab8d81d2f..d760c645441 100644
--- a/src/librustc/middle/trans/cabi.rs
+++ b/src/librustc/middle/trans/cabi.rs
@@ -94,7 +94,7 @@ pub fn compute_abi_info(ccx: &CrateContext,
                         atys: &[Type],
                         rty: Type,
                         ret_def: bool) -> FnType {
-    match ccx.sess.targ_cfg.arch {
+    match ccx.sess().targ_cfg.arch {
         X86 => cabi_x86::compute_abi_info(ccx, atys, rty, ret_def),
         X86_64 => cabi_x86_64::compute_abi_info(ccx, atys, rty, ret_def),
         Arm => cabi_arm::compute_abi_info(ccx, atys, rty, ret_def),
diff --git a/src/librustc/middle/trans/cabi_x86.rs b/src/librustc/middle/trans/cabi_x86.rs
index 194197e5011..dc099dba7d1 100644
--- a/src/librustc/middle/trans/cabi_x86.rs
+++ b/src/librustc/middle/trans/cabi_x86.rs
@@ -36,7 +36,7 @@ pub fn compute_abi_info(ccx: &CrateContext,
         // Clang's ABI handling is in lib/CodeGen/TargetInfo.cpp
 
         enum Strategy { RetValue(Type), RetPointer }
-        let strategy = match ccx.sess.targ_cfg.os {
+        let strategy = match ccx.sess().targ_cfg.os {
             OsWin32 | OsMacos => {
                 match llsize_of_alloc(ccx, rty) {
                     1 => RetValue(Type::i8()),
diff --git a/src/librustc/middle/trans/callee.rs b/src/librustc/middle/trans/callee.rs
index ff63b74444c..afa9e73c5f5 100644
--- a/src/librustc/middle/trans/callee.rs
+++ b/src/librustc/middle/trans/callee.rs
@@ -365,7 +365,7 @@ pub fn trans_fn_ref_with_vtables(
         true
     } else if def_id.krate == ast::LOCAL_CRATE {
         let map_node = session::expect(
-            ccx.sess,
+            ccx.sess(),
             ccx.tcx.map.find(def_id.node),
             || format!("local item should be in ast map"));
 
diff --git a/src/librustc/middle/trans/closure.rs b/src/librustc/middle/trans/closure.rs
index bfc9d8d2d6d..65b66700688 100644
--- a/src/librustc/middle/trans/closure.rs
+++ b/src/librustc/middle/trans/closure.rs
@@ -227,7 +227,7 @@ pub fn store_environment<'a>(
     for (i, bv) in bound_values.move_iter().enumerate() {
         debug!("Copy {} into closure", bv.to_str(ccx));
 
-        if ccx.sess.asm_comments() {
+        if ccx.sess().asm_comments() {
             add_comment(bcx, format!("Copy {} into closure",
                                   bv.to_str(ccx)));
         }
@@ -301,7 +301,7 @@ fn load_environment<'a>(bcx: &'a Block<'a>, cdata_ty: ty::t,
 
     // Store the pointer to closure data in an alloca for debug info because that's what the
     // llvm.dbg.declare intrinsic expects
-    let env_pointer_alloca = if bcx.ccx().sess.opts.debuginfo == FullDebugInfo {
+    let env_pointer_alloca = if bcx.sess().opts.debuginfo == FullDebugInfo {
         let alloc = alloc_ty(bcx, ty::mk_mut_ptr(bcx.tcx(), cdata_ty), "__debuginfo_env_ptr");
         Store(bcx, llcdata, alloc);
         Some(alloc)
@@ -419,9 +419,9 @@ pub fn get_wrapper_for_bare_fn(ccx: @CrateContext,
         ast::DefFn(did, _) | ast::DefStaticMethod(did, _, _) |
         ast::DefVariant(_, did, _) | ast::DefStruct(did) => did,
         _ => {
-            ccx.sess.bug(format!("get_wrapper_for_bare_fn: \
-                                  expected a statically resolved fn, got {:?}",
-                                  def));
+            ccx.sess().bug(format!("get_wrapper_for_bare_fn: \
+                                    expected a statically resolved fn, got {:?}",
+                                    def));
         }
     };
 
@@ -440,9 +440,9 @@ pub fn get_wrapper_for_bare_fn(ccx: @CrateContext,
     let f = match ty::get(closure_ty).sty {
         ty::ty_closure(ref f) => f,
         _ => {
-            ccx.sess.bug(format!("get_wrapper_for_bare_fn: \
-                                  expected a closure ty, got {}",
-                                  closure_ty.repr(tcx)));
+            ccx.sess().bug(format!("get_wrapper_for_bare_fn: \
+                                    expected a closure ty, got {}",
+                                    closure_ty.repr(tcx)));
         }
     };
 
diff --git a/src/librustc/middle/trans/common.rs b/src/librustc/middle/trans/common.rs
index bfe5d5187d7..5508cddefe0 100644
--- a/src/librustc/middle/trans/common.rs
+++ b/src/librustc/middle/trans/common.rs
@@ -383,13 +383,6 @@ impl<'a> FunctionContext<'a> {
     }
 }
 
-pub fn warn_not_to_commit(ccx: &mut CrateContext, msg: &str) {
-    if !ccx.do_not_commit_warning_issued.get() {
-        ccx.do_not_commit_warning_issued.set(true);
-        ccx.sess.warn(msg.to_str() + " -- do not commit like this!");
-    }
-}
-
 // Heap selectors. Indicate which heap something should go on.
 #[deriving(Eq)]
 pub enum heap {
@@ -446,7 +439,7 @@ impl<'a> Block<'a> {
     pub fn tcx(&self) -> ty::ctxt {
         self.fcx.ccx.tcx
     }
-    pub fn sess(&self) -> Session { self.fcx.ccx.sess }
+    pub fn sess(&self) -> &'a Session { self.fcx.ccx.sess() }
 
     pub fn ident(&self, ident: Ident) -> ~str {
         token::get_ident(ident).get().to_str()
diff --git a/src/librustc/middle/trans/consts.rs b/src/librustc/middle/trans/consts.rs
index 9d55084c7f4..ff548f06f0b 100644
--- a/src/librustc/middle/trans/consts.rs
+++ b/src/librustc/middle/trans/consts.rs
@@ -53,7 +53,7 @@ pub fn const_lit(cx: &CrateContext, e: &ast::Expr, lit: ast::Lit)
                 ty::ty_uint(t) => {
                     C_integral(Type::uint_from_ty(cx, t), i as u64, false)
                 }
-                _ => cx.sess.span_bug(lit.span,
+                _ => cx.sess().span_bug(lit.span,
                         format!("integer literal has type {} (expected int or uint)",
                                 ty_to_str(cx.tcx, lit_int_ty)))
             }
@@ -68,7 +68,7 @@ pub fn const_lit(cx: &CrateContext, e: &ast::Expr, lit: ast::Lit)
                     C_floating(fs.get(), Type::float_from_ty(t))
                 }
                 _ => {
-                    cx.sess.span_bug(lit.span,
+                    cx.sess().span_bug(lit.span,
                         "floating point literal doesn't have the right type");
                 }
             }
@@ -147,15 +147,15 @@ fn const_deref(cx: &CrateContext, v: ValueRef, t: ty::t, explicit: bool)
                     const_deref_newtype(cx, v, t)
                 }
                 _ => {
-                    cx.sess.bug(format!("unexpected dereferenceable type {}",
-                                     ty_to_str(cx.tcx, t)))
+                    cx.sess().bug(format!("unexpected dereferenceable type {}",
+                                          ty_to_str(cx.tcx, t)))
                 }
             };
             (dv, mt.ty)
         }
         None => {
-            cx.sess.bug(format!("can't dereference const of type {}",
-                             ty_to_str(cx.tcx, t)))
+            cx.sess().bug(format!("can't dereference const of type {}",
+                                  ty_to_str(cx.tcx, t)))
         }
     }
 }
@@ -210,7 +210,7 @@ pub fn const_expr(cx: @CrateContext, e: &ast::Expr, is_local: bool) -> (ValueRef
                     llconst = C_struct([wrapper, C_null(Type::i8p())], false)
                 }
                 ty::AutoAddEnv(ref r, ref s) => {
-                    cx.sess
+                    cx.sess()
                       .span_bug(e.span,
                                 format!("unexpected static function: region \
                                          {:?} sigil {:?}",
@@ -218,7 +218,7 @@ pub fn const_expr(cx: @CrateContext, e: &ast::Expr, is_local: bool) -> (ValueRef
                                         *s))
                 }
                 ty::AutoObject(..) => {
-                    cx.sess
+                    cx.sess()
                       .span_unimpl(e.span,
                                    "unimplemented const coercion to trait \
                                     object");
@@ -266,11 +266,11 @@ pub fn const_expr(cx: @CrateContext, e: &ast::Expr, is_local: bool) -> (ValueRef
                                     }
                                 }
                                 _ => {
-                                    cx.sess.span_bug(e.span,
-                                                     format!("unimplemented \
-                                                              const autoref \
-                                                              {:?}",
-                                                             autoref))
+                                    cx.sess().span_bug(e.span,
+                                                       format!("unimplemented \
+                                                                const autoref \
+                                                                {:?}",
+                                                               autoref))
                                 }
                             }
                         }
@@ -289,7 +289,7 @@ pub fn const_expr(cx: @CrateContext, e: &ast::Expr, is_local: bool) -> (ValueRef
             llvm::LLVMDumpValue(llconst);
             llvm::LLVMDumpValue(C_undef(llty));
         }
-        cx.sess.bug(format!("const {} of type {} has size {} instead of {}",
+        cx.sess().bug(format!("const {} of type {} has size {} instead of {}",
                          e.repr(cx.tcx), ty_to_str(cx.tcx, ety),
                          csize, tsize));
     }
@@ -440,8 +440,8 @@ fn const_expr_unadjusted(cx: @CrateContext, e: &ast::Expr,
               let iv = match const_eval::eval_const_expr(cx.tcx, index) {
                   const_eval::const_int(i) => i as u64,
                   const_eval::const_uint(u) => u,
-                  _ => cx.sess.span_bug(index.span,
-                                        "index is not an integer-constant expression")
+                  _ => cx.sess().span_bug(index.span,
+                                          "index is not an integer-constant expression")
               };
               let (arr, len) = match ty::get(bt).sty {
                   ty::ty_vec(_, vstore) | ty::ty_str(vstore) =>
@@ -453,11 +453,11 @@ fn const_expr_unadjusted(cx: @CrateContext, e: &ast::Expr,
                           let e1 = const_get_elt(cx, bv, [0]);
                           (const_deref_ptr(cx, e1), const_get_elt(cx, bv, [1]))
                       },
-                      _ => cx.sess.span_bug(base.span,
-                                            "index-expr base must be fixed-size or slice")
+                      _ => cx.sess().span_bug(base.span,
+                                              "index-expr base must be fixed-size or slice")
                   },
-                  _ =>  cx.sess.span_bug(base.span,
-                                         "index-expr base must be a vector or string type")
+                  _ =>  cx.sess().span_bug(base.span,
+                                           "index-expr base must be a vector or string type")
               };
 
               let len = llvm::LLVMConstIntGetZExtValue(len) as u64;
@@ -468,8 +468,8 @@ fn const_expr_unadjusted(cx: @CrateContext, e: &ast::Expr,
               if iv >= len {
                   // FIXME #3170: report this earlier on in the const-eval
                   // pass. Reporting here is a bit late.
-                  cx.sess.span_err(e.span,
-                                   "const index-expr is out of bounds");
+                  cx.sess().span_err(e.span,
+                                     "const index-expr is out of bounds");
               }
               (const_get_elt(cx, arr, [iv as c_uint]), inlineable)
           }
@@ -511,8 +511,8 @@ fn const_expr_unadjusted(cx: @CrateContext, e: &ast::Expr,
                         llvm::LLVMConstIntCast(iv, llty.to_ref(), s)
                     }
                     expr::cast_float => llvm::LLVMConstUIToFP(iv, llty.to_ref()),
-                    _ => cx.sess.bug("enum cast destination is not \
-                                      integral or float")
+                    _ => cx.sess().bug("enum cast destination is not \
+                                        integral or float")
                 }
               }
               (expr::cast_pointer, expr::cast_pointer) => {
@@ -522,8 +522,8 @@ fn const_expr_unadjusted(cx: @CrateContext, e: &ast::Expr,
                 llvm::LLVMConstIntToPtr(v, llty.to_ref())
               }
               _ => {
-                cx.sess.impossible_case(e.span,
-                                        "bad combination of types for cast")
+                cx.sess().impossible_case(e.span,
+                                          "bad combination of types for cast")
               }
             }, inlineable)
           }
@@ -558,7 +558,7 @@ fn const_expr_unadjusted(cx: @CrateContext, e: &ast::Expr,
                                     (adt::const_get_field(cx, repr, bv, discr, ix),
                                      inlineable)
                                 }
-                                None => cx.tcx.sess.span_bug(e.span, "missing struct field")
+                                None => cx.sess().span_bug(e.span, "missing struct field")
                               }
                           }
                       }
@@ -580,7 +580,7 @@ fn const_expr_unadjusted(cx: @CrateContext, e: &ast::Expr,
               ast::ExprLit(ref lit) => {
                 match lit.node {
                     ast::LitStr(..) => { const_expr(cx, sub, is_local) }
-                    _ => { cx.sess.span_bug(e.span, "bad const-slice lit") }
+                    _ => { cx.sess().span_bug(e.span, "bad const-slice lit") }
                 }
               }
               ast::ExprVec(ref es, ast::MutImmutable) => {
@@ -598,7 +598,7 @@ fn const_expr_unadjusted(cx: @CrateContext, e: &ast::Expr,
                 let p = const_ptrcast(cx, gv, llunitty);
                 (C_struct([p, C_uint(cx, es.len())], false), false)
               }
-              _ => cx.sess.span_bug(e.span, "bad const-slice expr")
+              _ => cx.sess().span_bug(e.span, "bad const-slice expr")
             }
           }
           ast::ExprRepeat(elem, count, _) => {
@@ -608,7 +608,7 @@ fn const_expr_unadjusted(cx: @CrateContext, e: &ast::Expr,
             let n = match const_eval::eval_const_expr(cx.tcx, count) {
                 const_eval::const_int(i)  => i as uint,
                 const_eval::const_uint(i) => i as uint,
-                _ => cx.sess.span_bug(count.span, "count must be integral const expression.")
+                _ => cx.sess().span_bug(count.span, "count must be integral const expression.")
             };
             let vs = vec::from_elem(n, const_expr(cx, elem, is_local).val0());
             let v = if vs.iter().any(|vi| val_ty(*vi) != llunitty) {
@@ -654,7 +654,7 @@ fn const_expr_unadjusted(cx: @CrateContext, e: &ast::Expr,
                     (C_null(llty), true)
                 }
                 _ => {
-                    cx.sess.span_bug(e.span, "expected a const, fn, struct, or variant def")
+                    cx.sess().span_bug(e.span, "expected a const, fn, struct, or variant def")
                 }
             }
           }
@@ -684,11 +684,11 @@ fn const_expr_unadjusted(cx: @CrateContext, e: &ast::Expr,
                                         vinfo.disr_val,
                                         arg_vals.as_slice()), inlineable)
                   }
-                  _ => cx.sess.span_bug(e.span, "expected a struct or variant def")
+                  _ => cx.sess().span_bug(e.span, "expected a struct or variant def")
               }
           }
           ast::ExprParen(e) => { const_expr(cx, e, is_local) }
-          _ => cx.sess.span_bug(e.span,
+          _ => cx.sess().span_bug(e.span,
                   "bad constant expression type in consts::const_expr")
         };
     }
diff --git a/src/librustc/middle/trans/context.rs b/src/librustc/middle/trans/context.rs
index 80dcfc90287..b8a29bfebe5 100644
--- a/src/librustc/middle/trans/context.rs
+++ b/src/librustc/middle/trans/context.rs
@@ -9,8 +9,8 @@
 // except according to those terms.
 
 
-use driver::session;
 use driver::session::NoDebugInfo;
+use driver::session::Session;
 use lib::llvm::{ContextRef, ModuleRef, ValueRef};
 use lib::llvm::{llvm, TargetData, TypeNames};
 use lib::llvm::mk_target_data;
@@ -39,7 +39,6 @@ use syntax::ast;
 use syntax::parse::token::InternedString;
 
 pub struct CrateContext {
-    sess: session::Session,
     llmod: ModuleRef,
     llcx: ContextRef,
     metadata_llmod: ModuleRef,
@@ -115,12 +114,10 @@ pub struct CrateContext {
     // is not emitted by LLVM's GC pass when no functions use GC.
     uses_gc: bool,
     dbg_cx: Option<debuginfo::CrateDebugContext>,
-    do_not_commit_warning_issued: Cell<bool>,
 }
 
 impl CrateContext {
-    pub fn new(sess: session::Session,
-               name: &str,
+    pub fn new(name: &str,
                tcx: ty::ctxt,
                emap2: resolve::ExportMap2,
                maps: astencode::Maps,
@@ -137,8 +134,8 @@ impl CrateContext {
             let metadata_llmod = format!("{}_metadata", name).with_c_str(|buf| {
                 llvm::LLVMModuleCreateWithNameInContext(buf, llcx)
             });
-            let data_layout: &str = sess.targ_cfg.target_strs.data_layout;
-            let targ_triple: &str = sess.targ_cfg.target_strs.target_triple;
+            let data_layout: &str = tcx.sess.targ_cfg.target_strs.data_layout;
+            let targ_triple: &str = tcx.sess.targ_cfg.target_strs.target_triple;
             data_layout.with_c_str(|buf| {
                 llvm::LLVMSetDataLayout(llmod, buf);
                 llvm::LLVMSetDataLayout(metadata_llmod, buf);
@@ -147,13 +144,13 @@ impl CrateContext {
                 llvm::LLVMRustSetNormalizedTarget(llmod, buf);
                 llvm::LLVMRustSetNormalizedTarget(metadata_llmod, buf);
             });
-            let targ_cfg = sess.targ_cfg;
+            let targ_cfg = tcx.sess.targ_cfg;
 
-            let td = mk_target_data(sess.targ_cfg.target_strs.data_layout);
+            let td = mk_target_data(tcx.sess.targ_cfg.target_strs.data_layout);
             let tn = TypeNames::new();
 
             let mut intrinsics = base::declare_intrinsics(llmod);
-            if sess.opts.debuginfo != NoDebugInfo {
+            if tcx.sess.opts.debuginfo != NoDebugInfo {
                 base::declare_dbg_intrinsics(llmod, &mut intrinsics);
             }
             let int_type = Type::int(targ_cfg.arch);
@@ -166,19 +163,18 @@ impl CrateContext {
             tn.associate_type("tydesc", &tydesc_type);
             tn.associate_type("str_slice", &str_slice_ty);
 
-            let (crate_map_name, crate_map) = decl_crate_map(sess, link_meta.clone(), llmod);
-            let dbg_cx = if sess.opts.debuginfo != NoDebugInfo {
+            let (crate_map_name, crate_map) = decl_crate_map(&tcx.sess, link_meta.clone(), llmod);
+            let dbg_cx = if tcx.sess.opts.debuginfo != NoDebugInfo {
                 Some(debuginfo::CrateDebugContext::new(llmod))
             } else {
                 None
             };
 
-            if sess.count_llvm_insns() {
+            if tcx.sess.count_llvm_insns() {
                 base::init_insn_ctxt()
             }
 
             CrateContext {
-                 sess: sess,
                  llmod: llmod,
                  llcx: llcx,
                  metadata_llmod: metadata_llmod,
@@ -235,11 +231,14 @@ impl CrateContext {
                  crate_map_name: crate_map_name,
                  uses_gc: false,
                  dbg_cx: dbg_cx,
-                 do_not_commit_warning_issued: Cell::new(false),
             }
         }
     }
 
+    pub fn sess<'a>(&'a self) -> &'a Session {
+        &self.tcx.sess
+    }
+
     pub fn builder<'a>(&'a self) -> Builder<'a> {
         Builder::new(self)
     }
diff --git a/src/librustc/middle/trans/debuginfo.rs b/src/librustc/middle/trans/debuginfo.rs
index dd6a3e61b69..cf9a4aaedb8 100644
--- a/src/librustc/middle/trans/debuginfo.rs
+++ b/src/librustc/middle/trans/debuginfo.rs
@@ -213,10 +213,10 @@ impl FunctionDebugContext {
         match *self {
             FunctionDebugContext(~ref data) => data,
             DebugInfoDisabled => {
-                cx.sess.span_bug(span, FunctionDebugContext::debuginfo_disabled_message());
+                cx.sess().span_bug(span, FunctionDebugContext::debuginfo_disabled_message());
             }
             FunctionWithoutDebugInfo => {
-                cx.sess.span_bug(span, FunctionDebugContext::should_be_ignored_message());
+                cx.sess().span_bug(span, FunctionDebugContext::should_be_ignored_message());
             }
         }
     }
@@ -268,7 +268,7 @@ pub fn finalize(cx: @CrateContext) {
         // instruct LLVM to emit an older version of dwarf, however,
         // for OS X to understand. For more info see #11352
         // This can be overridden using --llvm-opts -dwarf-version,N.
-        if cx.sess.targ_cfg.os == abi::OsMacos {
+        if cx.sess().targ_cfg.os == abi::OsMacos {
             "Dwarf Version".with_c_str(
                 |s| llvm::LLVMRustAddModuleFlag(cx.llmod, s, 2));
         }
@@ -299,7 +299,7 @@ pub fn create_local_var_metadata(bcx: &Block, local: &ast::Local) {
             match lllocals.get().find_copy(&node_id) {
                 Some(datum) => datum,
                 None => {
-                    bcx.tcx().sess.span_bug(span,
+                    bcx.sess().span_bug(span,
                         format!("no entry in lllocals table for {:?}",
                                 node_id));
                 }
@@ -338,7 +338,7 @@ pub fn create_captured_var_metadata(bcx: &Block,
 
     let variable_ident = match ast_item {
         None => {
-            cx.sess.span_bug(span, "debuginfo::create_captured_var_metadata() - NodeId not found");
+            cx.sess().span_bug(span, "debuginfo::create_captured_var_metadata: node not found");
         }
         Some(ast_map::NodeLocal(pat)) | Some(ast_map::NodeArg(pat)) => {
             match pat.node {
@@ -346,7 +346,7 @@ pub fn create_captured_var_metadata(bcx: &Block,
                     ast_util::path_to_ident(path)
                 }
                 _ => {
-                    cx.sess
+                    cx.sess()
                       .span_bug(span,
                                 format!(
                                 "debuginfo::create_captured_var_metadata() - \
@@ -357,7 +357,7 @@ pub fn create_captured_var_metadata(bcx: &Block,
             }
         }
         _ => {
-            cx.sess.span_bug(span, format!("debuginfo::create_captured_var_metadata() - \
+            cx.sess().span_bug(span, format!("debuginfo::create_captured_var_metadata() - \
                 Captured var-id refers to unexpected ast_map variant: {:?}", ast_item));
         }
     };
@@ -441,7 +441,7 @@ pub fn create_argument_metadata(bcx: &Block, arg: &ast::Arg) {
             match llargs.get().find_copy(&node_id) {
                 Some(v) => v,
                 None => {
-                    bcx.tcx().sess.span_bug(span,
+                    bcx.sess().span_bug(span,
                         format!("no entry in llargs table for {:?}",
                                 node_id));
                 }
@@ -449,7 +449,7 @@ pub fn create_argument_metadata(bcx: &Block, arg: &ast::Arg) {
         };
 
         if unsafe { llvm::LLVMIsAAllocaInst(llarg.val) } == ptr::null() {
-            cx.sess.span_bug(span, "debuginfo::create_argument_metadata() - \
+            cx.sess().span_bug(span, "debuginfo::create_argument_metadata() - \
                                     Referenced variable location is not an alloca!");
         }
 
@@ -485,7 +485,7 @@ pub fn set_source_location(fcx: &FunctionContext,
 
     let cx = fcx.ccx;
 
-    debug!("set_source_location: {}", cx.sess.codemap.span_to_str(span));
+    debug!("set_source_location: {}", cx.sess().codemap.span_to_str(span));
 
     if fcx.debug_context.get_ref(cx, span).source_locations_enabled.get() {
         let loc = span_start(cx, span);
@@ -532,7 +532,7 @@ pub fn create_function_debug_context(cx: &CrateContext,
                                      fn_ast_id: ast::NodeId,
                                      param_substs: Option<@param_substs>,
                                      llfn: ValueRef) -> FunctionDebugContext {
-    if cx.sess.opts.debuginfo == NoDebugInfo {
+    if cx.sess().opts.debuginfo == NoDebugInfo {
         return DebugInfoDisabled;
     }
 
@@ -551,7 +551,7 @@ pub fn create_function_debug_context(cx: &CrateContext,
                     (item.ident, fn_decl, generics, top_level_block, item.span, true)
                 }
                 _ => {
-                    cx.sess.span_bug(item.span,
+                    cx.sess().span_bug(item.span,
                         "create_function_debug_context: item bound to non-function");
                 }
             }
@@ -579,7 +579,7 @@ pub fn create_function_debug_context(cx: &CrateContext,
                         // Don't try to lookup the item path:
                         false)
                 }
-                _ => cx.sess.span_bug(expr.span,
+                _ => cx.sess().span_bug(expr.span,
                         "create_function_debug_context: expected an expr_fn_block here")
             }
         }
@@ -594,7 +594,7 @@ pub fn create_function_debug_context(cx: &CrateContext,
                      true)
                 }
                 _ => {
-                    cx.sess
+                    cx.sess()
                       .bug(format!("create_function_debug_context: \
                                     unexpected sort of node: {:?}",
                                     fnitem))
@@ -606,8 +606,8 @@ pub fn create_function_debug_context(cx: &CrateContext,
         ast_map::NodeStructCtor(..) => {
             return FunctionWithoutDebugInfo;
         }
-        _ => cx.sess.bug(format!("create_function_debug_context: \
-                                  unexpected sort of node: {:?}", fnitem))
+        _ => cx.sess().bug(format!("create_function_debug_context: \
+                                    unexpected sort of node: {:?}", fnitem))
     };
 
     // This can be the case for functions inlined from another crate
@@ -672,7 +672,7 @@ pub fn create_function_debug_context(cx: &CrateContext,
                     true,
                     scope_line as c_uint,
                     FlagPrototyped as c_uint,
-                    cx.sess.opts.optimize != session::No,
+                    cx.sess().opts.optimize != session::No,
                     llfn,
                     template_parameters,
                     ptr::null())
@@ -708,7 +708,7 @@ pub fn create_function_debug_context(cx: &CrateContext,
                               fn_decl: &ast::FnDecl,
                               param_substs: Option<@param_substs>,
                               error_span: Span) -> DIArray {
-        if cx.sess.opts.debuginfo == LimitedDebugInfo {
+        if cx.sess().opts.debuginfo == LimitedDebugInfo {
             return create_DIArray(DIB(cx), []);
         }
 
@@ -793,7 +793,7 @@ pub fn create_function_debug_context(cx: &CrateContext,
             }
 
             // Only create type information if full debuginfo is enabled
-            if cx.sess.opts.debuginfo == FullDebugInfo {
+            if cx.sess().opts.debuginfo == FullDebugInfo {
                 let actual_self_type_metadata = type_metadata(cx,
                                                               actual_self_type,
                                                               codemap::DUMMY_SP);
@@ -837,7 +837,7 @@ pub fn create_function_debug_context(cx: &CrateContext,
             }
 
             // Again, only create type information if full debuginfo is enabled
-            if cx.sess.opts.debuginfo == FullDebugInfo {
+            if cx.sess().opts.debuginfo == FullDebugInfo {
                 let actual_type_metadata = type_metadata(cx, actual_type, codemap::DUMMY_SP);
                 let param_metadata = token::get_ident(ident).get()
                                                             .with_c_str(|name| {
@@ -873,12 +873,12 @@ fn create_DIArray(builder: DIBuilderRef, arr: &[DIDescriptor]) -> DIArray {
 }
 
 fn compile_unit_metadata(cx: &CrateContext) {
-    let work_dir = &cx.sess.working_dir;
-    let compile_unit_name = match cx.sess.local_crate_source_file {
+    let work_dir = &cx.sess().working_dir;
+    let compile_unit_name = match cx.sess().local_crate_source_file {
         None => fallback_path(cx),
         Some(ref abs_path) => {
             if abs_path.is_relative() {
-                cx.sess.warn("debuginfo: Invalid path to crate's local root source file!");
+                cx.sess().warn("debuginfo: Invalid path to crate's local root source file!");
                 fallback_path(cx)
             } else {
                 match abs_path.path_relative_from(work_dir) {
@@ -917,7 +917,7 @@ fn compile_unit_metadata(cx: &CrateContext) {
                                 compile_unit_name,
                                 work_dir,
                                 producer,
-                                cx.sess.opts.optimize != session::No,
+                                cx.sess().opts.optimize != session::No,
                                 flags,
                                 0,
                                 split_name);
@@ -968,7 +968,7 @@ fn declare_local(bcx: &Block,
                         file_metadata,
                         loc.line as c_uint,
                         type_metadata,
-                        cx.sess.opts.optimize != session::No,
+                        cx.sess().opts.optimize != session::No,
                         0,
                         argument_index)
                 }
@@ -1028,7 +1028,7 @@ fn file_metadata(cx: &CrateContext, full_path: &str) -> DIFile {
     debug!("file_metadata: {}", full_path);
 
     // FIXME (#9639): This needs to handle non-utf8 paths
-    let work_dir = cx.sess.working_dir.as_str().unwrap();
+    let work_dir = cx.sess().working_dir.as_str().unwrap();
     let file_name =
         if full_path.starts_with(work_dir) {
             full_path.slice(work_dir.len() + 1u, full_path.len())
@@ -1063,7 +1063,7 @@ fn scope_metadata(fcx: &FunctionContext,
         None => {
             let node = fcx.ccx.tcx.map.get(node_id);
 
-            fcx.ccx.sess.span_bug(span,
+            fcx.ccx.sess().span_bug(span,
                 format!("debuginfo: Could not find scope info for node {:?}", node));
         }
     }
@@ -1096,7 +1096,7 @@ fn basic_type_metadata(cx: &CrateContext, t: ty::t) -> DIType {
             ast::TyF32 => (~"f32", DW_ATE_float),
             ast::TyF64 => (~"f64", DW_ATE_float)
         },
-        _ => cx.sess.bug("debuginfo::basic_type_metadata - t is invalid type")
+        _ => cx.sess().bug("debuginfo::basic_type_metadata - t is invalid type")
     };
 
     let llvm_type = type_of::type_of(cx, t);
@@ -1329,7 +1329,7 @@ impl GeneralMemberDescriptionFactory {
         // Capture type_rep, so we don't have to copy the struct_defs array
         let struct_defs = match *self.type_rep {
             adt::General(_, ref struct_defs) => struct_defs,
-            _ => cx.sess.bug("unreachable")
+            _ => cx.sess().bug("unreachable")
         };
 
         struct_defs
@@ -1653,9 +1653,9 @@ fn set_members_of_composite_type(cx: &CrateContext,
         let mut composite_types_completed =
             debug_context(cx).composite_types_completed.borrow_mut();
         if composite_types_completed.get().contains(&composite_type_metadata) {
-            cx.sess.span_bug(definition_span, "debuginfo::set_members_of_composite_type() - \
-                                               Already completed forward declaration \
-                                               re-encountered.");
+            cx.sess().span_bug(definition_span, "debuginfo::set_members_of_composite_type() - \
+                                                 Already completed forward declaration \
+                                                 re-encountered.");
         } else {
             composite_types_completed.get().insert(composite_type_metadata);
         }
@@ -1856,7 +1856,7 @@ fn vec_metadata(cx: &CrateContext,
     let element_llvm_type = type_of::type_of(cx, element_type);
     let (element_size, element_align) = size_and_align_of(cx, element_llvm_type);
 
-    let vec_llvm_type = Type::vec(cx.sess.targ_cfg.arch, &element_llvm_type);
+    let vec_llvm_type = Type::vec(cx.sess().targ_cfg.arch, &element_llvm_type);
     let vec_type_name: &str = format!("[{}]", ppaux::ty_to_str(cx.tcx, element_type));
 
     let member_llvm_types = vec_llvm_type.field_types();
@@ -2144,7 +2144,7 @@ fn type_metadata(cx: &CrateContext,
                                    elements.as_slice(),
                                    usage_site_span).finalize(cx)
         }
-        _ => cx.sess.bug(format!("debuginfo: unexpected type in type_metadata: {:?}", sty))
+        _ => cx.sess().bug(format!("debuginfo: unexpected type in type_metadata: {:?}", sty))
     };
 
     let mut created_types = debug_context(cx).created_types.borrow_mut();
@@ -2218,7 +2218,7 @@ fn generate_unique_type_id(prefix: &'static str) -> ~str {
 
 /// Return codemap::Loc corresponding to the beginning of the span
 fn span_start(cx: &CrateContext, span: Span) -> codemap::Loc {
-    cx.sess.codemap.lookup_char_pos(span.lo)
+    cx.sess().codemap.lookup_char_pos(span.lo)
 }
 
 fn size_and_align_of(cx: &CrateContext, llvm_type: Type) -> (u64, u64) {
@@ -2250,7 +2250,7 @@ fn fn_should_be_ignored(fcx: &FunctionContext) -> bool {
 fn assert_type_for_node_id(cx: &CrateContext, node_id: ast::NodeId, error_span: Span) {
     let node_types = cx.tcx.node_types.borrow();
     if !node_types.get().contains_key(&(node_id as uint)) {
-        cx.sess.span_bug(error_span, "debuginfo: Could not find type for node id!");
+        cx.sess().span_bug(error_span, "debuginfo: Could not find type for node id!");
     }
 }
 
@@ -2315,7 +2315,7 @@ fn populate_scope_map(cx: &CrateContext,
                                    &mut Vec<ScopeStackEntry> ,
                                    &mut HashMap<ast::NodeId, DIScope>|) {
         // Create a new lexical scope and push it onto the stack
-        let loc = cx.sess.codemap.lookup_char_pos(scope_span.lo);
+        let loc = cx.sess().codemap.lookup_char_pos(scope_span.lo);
         let file_metadata = file_metadata(cx, loc.file.name);
         let parent_scope = scope_stack.last().unwrap().scope_metadata;
 
@@ -2338,7 +2338,7 @@ fn populate_scope_map(cx: &CrateContext,
         }
 
         if scope_stack.last().unwrap().scope_metadata != scope_metadata {
-            cx.sess.span_bug(scope_span, "debuginfo: Inconsistency in scope management.");
+            cx.sess().span_bug(scope_span, "debuginfo: Inconsistency in scope management.");
         }
 
         scope_stack.pop();
@@ -2432,7 +2432,7 @@ fn populate_scope_map(cx: &CrateContext,
 
                     if need_new_scope {
                         // Create a new lexical scope and push it onto the stack
-                        let loc = cx.sess.codemap.lookup_char_pos(pat.span.lo);
+                        let loc = cx.sess().codemap.lookup_char_pos(pat.span.lo);
                         let file_metadata = file_metadata(cx, loc.file.name);
                         let parent_scope = scope_stack.last().unwrap().scope_metadata;
 
@@ -2614,13 +2614,13 @@ fn populate_scope_map(cx: &CrateContext,
             }
 
             ast::ExprForLoop(_, _, _, _) => {
-                cx.sess.span_bug(exp.span, "debuginfo::populate_scope_map() - \
-                                            Found unexpanded for-loop.");
+                cx.sess().span_bug(exp.span, "debuginfo::populate_scope_map() - \
+                                              Found unexpanded for-loop.");
             }
 
             ast::ExprMac(_) => {
-                cx.sess.span_bug(exp.span, "debuginfo::populate_scope_map() - \
-                                            Found unexpanded macro.");
+                cx.sess().span_bug(exp.span, "debuginfo::populate_scope_map() - \
+                                              Found unexpanded macro.");
             }
 
             ast::ExprLoop(block, _) |
@@ -2827,7 +2827,7 @@ fn namespace_for_item(cx: &CrateContext, def_id: ast::DefId) -> @NamespaceTreeNo
         match parent_node {
             Some(node) => node,
             None => {
-                cx.sess.bug(format!("debuginfo::namespace_for_item(): \
+                cx.sess().bug(format!("debuginfo::namespace_for_item(): \
                     path too short for {:?}", def_id));
             }
         }
diff --git a/src/librustc/middle/trans/expr.rs b/src/librustc/middle/trans/expr.rs
index bf2d192d0de..55259cdae1c 100644
--- a/src/librustc/middle/trans/expr.rs
+++ b/src/librustc/middle/trans/expr.rs
@@ -581,7 +581,7 @@ fn trans_def<'a>(bcx: &'a Block<'a>,
                     unsafe {
                         let llty = type_of::type_of(bcx.ccx(), const_ty);
                         let symbol = csearch::get_symbol(
-                            bcx.ccx().sess.cstore,
+                            bcx.ccx().sess().cstore,
                             did);
                         let llval = symbol.with_c_str(|buf| {
                                 llvm::LLVMAddGlobal(bcx.ccx().llmod,
@@ -1618,16 +1618,16 @@ fn trans_imm_cast<'a>(bcx: &'a Block<'a>,
                                           val_ty(lldiscrim_a),
                                           lldiscrim_a, true),
                 cast_float => SIToFP(bcx, lldiscrim_a, ll_t_out),
-                _ => ccx.sess.bug(format!("translating unsupported cast: \
-                                          {} ({:?}) -> {} ({:?})",
-                                          t_in.repr(ccx.tcx), k_in,
-                                          t_out.repr(ccx.tcx), k_out))
+                _ => ccx.sess().bug(format!("translating unsupported cast: \
+                                            {} ({:?}) -> {} ({:?})",
+                                            t_in.repr(ccx.tcx), k_in,
+                                            t_out.repr(ccx.tcx), k_out))
             }
         }
-        _ => ccx.sess.bug(format!("translating unsupported cast: \
-                                  {} ({:?}) -> {} ({:?})",
-                                  t_in.repr(ccx.tcx), k_in,
-                                  t_out.repr(ccx.tcx), k_out))
+        _ => ccx.sess().bug(format!("translating unsupported cast: \
+                                    {} ({:?}) -> {} ({:?})",
+                                    t_in.repr(ccx.tcx), k_in,
+                                    t_out.repr(ccx.tcx), k_out))
     };
     return immediate_rvalue_bcx(bcx, newval, t_out).to_expr_datumblock();
 }
@@ -1665,7 +1665,6 @@ fn trans_assign_op<'a>(
     return result_datum.store_to(bcx, dst_datum.val);
 }
 
-
 fn auto_ref<'a>(bcx: &'a Block<'a>,
                 datum: Datum<Expr>,
                 expr: &ast::Expr)
diff --git a/src/librustc/middle/trans/foreign.rs b/src/librustc/middle/trans/foreign.rs
index f37d4b9859d..ab3339339d2 100644
--- a/src/librustc/middle/trans/foreign.rs
+++ b/src/librustc/middle/trans/foreign.rs
@@ -75,23 +75,23 @@ struct LlvmSignature {
 
 pub fn llvm_calling_convention(ccx: &CrateContext,
                                abis: AbiSet) -> Option<CallConv> {
-    let os = ccx.sess.targ_cfg.os;
-    let arch = ccx.sess.targ_cfg.arch;
+    let os = ccx.sess().targ_cfg.os;
+    let arch = ccx.sess().targ_cfg.arch;
     abis.for_target(os, arch).map(|abi| {
         match abi {
             RustIntrinsic => {
                 // Intrinsics are emitted by monomorphic fn
-                ccx.sess.bug(format!("asked to register intrinsic fn"));
+                ccx.sess().bug(format!("asked to register intrinsic fn"));
             }
 
             Rust => {
                 // FIXME(#3678) Implement linking to foreign fns with Rust ABI
-                ccx.sess.unimpl(
+                ccx.sess().unimpl(
                     format!("foreign functions with Rust ABI"));
             }
 
             // It's the ABI's job to select this, not us.
-            System => ccx.sess.bug("system abi should be selected elsewhere"),
+            System => ccx.sess().bug("system abi should be selected elsewhere"),
 
             Stdcall => lib::llvm::X86StdcallCallConv,
             Fastcall => lib::llvm::X86FastcallCallConv,
@@ -222,7 +222,7 @@ pub fn register_foreign_item_fn(ccx: @CrateContext, abis: AbiSet,
     let cc = match llvm_calling_convention(ccx, abis) {
         Some(cc) => cc,
         None => {
-            ccx.sess.span_fatal(foreign_item.span,
+            ccx.sess().span_fatal(foreign_item.span,
                 format!("ABI `{}` has no suitable calling convention \
                       for target architecture",
                       abis.user_string(ccx.tcx)));
@@ -294,7 +294,7 @@ pub fn trans_native_call<'a>(
 
     let (fn_abis, fn_sig) = match ty::get(callee_ty).sty {
         ty::ty_bare_fn(ref fn_ty) => (fn_ty.abis, fn_ty.sig.clone()),
-        _ => ccx.sess.bug("trans_native_call called on non-function type")
+        _ => ccx.sess().bug("trans_native_call called on non-function type")
     };
     let llsig = foreign_signature(ccx, &fn_sig, passed_arg_tys.as_slice());
     let ret_def = !return_type_is_void(bcx.ccx(), fn_sig.output);
@@ -383,7 +383,7 @@ pub fn trans_native_call<'a>(
         Some(cc) => cc,
         None => {
             // FIXME(#8357) We really ought to report a span here
-            ccx.sess.fatal(
+            ccx.sess().fatal(
                 format!("ABI string `{}` has no suitable ABI \
                         for target architecture",
                         fn_abis.user_string(ccx.tcx)));
@@ -563,10 +563,10 @@ pub fn trans_rust_fn_with_foreign_abi(ccx: @CrateContext,
                 f
             }
             _ => {
-                ccx.sess.bug(format!("build_rust_fn: extern fn {} has ty {}, \
-                                  expected a bare fn ty",
-                                  ccx.tcx.map.path_to_str(id),
-                                  t.repr(tcx)));
+                ccx.sess().bug(format!("build_rust_fn: extern fn {} has ty {}, \
+                                       expected a bare fn ty",
+                                       ccx.tcx.map.path_to_str(id),
+                                       t.repr(tcx)));
             }
         };
 
@@ -860,7 +860,7 @@ fn foreign_types_for_fn_ty(ccx: &CrateContext,
                            ty: ty::t) -> ForeignTypes {
     let fn_sig = match ty::get(ty).sty {
         ty::ty_bare_fn(ref fn_ty) => fn_ty.sig.clone(),
-        _ => ccx.sess.bug("foreign_types_for_fn_ty called on non-function type")
+        _ => ccx.sess().bug("foreign_types_for_fn_ty called on non-function type")
     };
     let llsig = foreign_signature(ccx, &fn_sig, fn_sig.inputs.as_slice());
     let ret_def = !return_type_is_void(ccx, fn_sig.output);
diff --git a/src/librustc/middle/trans/glue.rs b/src/librustc/middle/trans/glue.rs
index 6d4737eeff1..11fc2fcdc09 100644
--- a/src/librustc/middle/trans/glue.rs
+++ b/src/librustc/middle/trans/glue.rs
@@ -173,7 +173,7 @@ pub fn call_visit_glue(bcx: &Block, v: ValueRef, tydesc: ValueRef,
     let ccx = bcx.ccx();
     // NB: Don't short-circuit even if this block is unreachable because
     // GC-based cleanup needs to the see that the roots are live.
-    if bcx.unreachable.get() && !ccx.sess.no_landing_pads() { return; }
+    if bcx.unreachable.get() && !ccx.sess().no_landing_pads() { return; }
 
     let static_glue_fn = match static_ti {
         None => None,
@@ -403,7 +403,7 @@ pub fn declare_tydesc(ccx: &CrateContext, t: ty::t) -> @tydesc_info {
 
     let llty = type_of(ccx, t);
 
-    if ccx.sess.count_type_sizes() {
+    if ccx.sess().count_type_sizes() {
         println!("{}\t{}", llsize_of_real(ccx, llty),
                  ppaux::ty_to_str(ccx.tcx, t));
     }
diff --git a/src/librustc/middle/trans/inline.rs b/src/librustc/middle/trans/inline.rs
index 896d97f0374..0ab113a546f 100644
--- a/src/librustc/middle/trans/inline.rs
+++ b/src/librustc/middle/trans/inline.rs
@@ -122,14 +122,14 @@ pub fn maybe_instantiate_inline(ccx: @CrateContext, fn_id: ast::DefId)
                 }
               }
             }
-            _ => ccx.sess.bug("maybe_instantiate_inline: item has a \
-                               non-enum, non-struct parent")
+            _ => ccx.sess().bug("maybe_instantiate_inline: item has a \
+                                 non-enum, non-struct parent")
           }
           trans_item(ccx, item);
           local_def(my_id)
         }
         csearch::found_parent(_, _) => {
-            ccx.sess.bug("maybe_get_item_ast returned a found_parent \
+            ccx.sess().bug("maybe_get_item_ast returned a found_parent \
              with a non-item parent");
         }
         csearch::found(ast::IIMethod(impl_did, is_provided, mth)) => {
diff --git a/src/librustc/middle/trans/intrinsic.rs b/src/librustc/middle/trans/intrinsic.rs
index 1a5d794c1a4..c4208906043 100644
--- a/src/librustc/middle/trans/intrinsic.rs
+++ b/src/librustc/middle/trans/intrinsic.rs
@@ -218,7 +218,7 @@ pub fn trans_intrinsic(ccx: @CrateContext,
                 "acq"     => lib::llvm::Acquire,
                 "rel"     => lib::llvm::Release,
                 "acqrel"  => lib::llvm::AcquireRelease,
-                _ => ccx.sess.fatal("unknown ordering in atomic intrinsic")
+                _ => ccx.sess().fatal("unknown ordering in atomic intrinsic")
             }
         };
 
@@ -259,7 +259,7 @@ pub fn trans_intrinsic(ccx: @CrateContext,
                     "min"   => lib::llvm::Min,
                     "umax"  => lib::llvm::UMax,
                     "umin"  => lib::llvm::UMin,
-                    _ => ccx.sess.fatal("unknown atomic operation")
+                    _ => ccx.sess().fatal("unknown atomic operation")
                 };
 
                 let old = AtomicRMW(bcx, atom_op, get_param(decl, first_real_arg),
@@ -377,7 +377,7 @@ pub fn trans_intrinsic(ccx: @CrateContext,
                     ast_map::NodeExpr(e) => e.span,
                     _ => fail!("transmute has non-expr arg"),
                 };
-                ccx.sess.span_fatal(sp,
+                ccx.sess().span_fatal(sp,
                     format!("transmute called on types with different sizes: \
                              {intype} ({insize, plural, =1{# bit} other{# bits}}) to \
                              {outtype} ({outsize, plural, =1{# bit} other{# bits}})",
@@ -527,7 +527,7 @@ pub fn trans_intrinsic(ccx: @CrateContext,
         _ => {
             // Could we make this an enum rather than a string? does it get
             // checked earlier?
-            ccx.sess.span_bug(item.span, "unknown intrinsic");
+            ccx.sess().span_bug(item.span, "unknown intrinsic");
         }
     }
     fcx.cleanup();
diff --git a/src/librustc/middle/trans/meth.rs b/src/librustc/middle/trans/meth.rs
index 89f33776431..68f21a6ff0b 100644
--- a/src/librustc/middle/trans/meth.rs
+++ b/src/librustc/middle/trans/meth.rs
@@ -108,8 +108,8 @@ pub fn trans_method_callee<'a>(
             (method.origin, method.ty)
         }
         None => {
-            bcx.tcx().sess.span_bug(bcx.tcx().map.span(method_call.expr_id),
-                                    "method call expr wasn't in method map")
+            bcx.sess().span_bug(bcx.tcx().map.span(method_call.expr_id),
+                                "method call expr wasn't in method map")
         }
     };
 
@@ -145,9 +145,9 @@ pub fn trans_method_callee<'a>(
             let self_expr = match self_expr {
                 Some(self_expr) => self_expr,
                 None => {
-                    bcx.tcx().sess.span_bug(bcx.tcx().map.span(method_call.expr_id),
-                                            "self expr wasn't provided for trait object \
-                                            callee (trying to call overloaded op?)")
+                    bcx.sess().span_bug(bcx.tcx().map.span(method_call.expr_id),
+                                        "self expr wasn't provided for trait object \
+                                         callee (trying to call overloaded op?)")
                 }
             };
             trans_trait_callee(bcx,
@@ -425,7 +425,7 @@ pub fn trans_trait_callee_from_llval<'a>(bcx: &'a Block<'a>,
             type_of_rust_fn(ccx, true, f.sig.inputs.slice_from(1), f.sig.output)
         }
         _ => {
-            ccx.sess.bug("meth::trans_trait_callee given non-bare-rust-fn");
+            ccx.sess().bug("meth::trans_trait_callee given non-bare-rust-fn");
         }
     };
     let llvtable = Load(bcx,
@@ -500,7 +500,7 @@ pub fn get_vtable(bcx: &Block,
                     methods.push(vtable_method)
                 }
             }
-            _ => ccx.sess.bug("get_vtable: expected a static origin"),
+            _ => ccx.sess().bug("get_vtable: expected a static origin"),
         }
     }
 
@@ -548,8 +548,8 @@ fn emit_vtable_methods(bcx: &Block,
 
     let trt_id = match ty::impl_trait_ref(tcx, impl_id) {
         Some(t_id) => t_id.def_id,
-        None       => ccx.sess.bug("make_impl_vtable: don't know how to \
-                                    make a vtable for a type impl!")
+        None       => ccx.sess().bug("make_impl_vtable: don't know how to \
+                                      make a vtable for a type impl!")
     };
 
     ty::populate_implementations_for_trait_if_necessary(bcx.tcx(), trt_id);
diff --git a/src/librustc/middle/trans/monomorphize.rs b/src/librustc/middle/trans/monomorphize.rs
index b39bcfb075f..4a5dcf148e0 100644
--- a/src/librustc/middle/trans/monomorphize.rs
+++ b/src/librustc/middle/trans/monomorphize.rs
@@ -95,7 +95,7 @@ pub fn monomorphic_fn(ccx: @CrateContext,
     let mut is_static_provided = None;
 
     let map_node = session::expect(
-        ccx.sess,
+        ccx.sess(),
         ccx.tcx.map.find(fn_id.node),
         || format!("while monomorphizing {:?}, couldn't find it in the \
                     item map (may have attempted to monomorphize an item \
@@ -172,8 +172,8 @@ pub fn monomorphic_fn(ccx: @CrateContext,
         // Random cut-off -- code that needs to instantiate the same function
         // recursively more than thirty times can probably safely be assumed
         // to be causing an infinite expansion.
-        if depth > ccx.sess.recursion_limit.get() {
-            ccx.sess.span_fatal(ccx.tcx.map.span(fn_id.node),
+        if depth > ccx.sess().recursion_limit.get() {
+            ccx.sess().span_fatal(ccx.tcx.map.span(fn_id.node),
                 "reached the recursion limit during monomorphization");
         }
 
@@ -207,7 +207,7 @@ pub fn monomorphic_fn(ccx: @CrateContext,
                   d
               }
               _ => {
-                ccx.tcx.sess.bug("Can't monomorphize this kind of item")
+                ccx.sess().bug("Can't monomorphize this kind of item")
               }
             }
         }
@@ -239,7 +239,7 @@ pub fn monomorphic_fn(ccx: @CrateContext,
                                        d);
                 }
                 ast::StructVariantKind(_) =>
-                    ccx.tcx.sess.bug("can't monomorphize struct variants"),
+                    ccx.sess().bug("can't monomorphize struct variants"),
             }
             d
         }
@@ -258,8 +258,8 @@ pub fn monomorphic_fn(ccx: @CrateContext,
                     d
                 }
                 _ => {
-                    ccx.tcx.sess.bug(format!("can't monomorphize a {:?}",
-                                             map_node))
+                    ccx.sess().bug(format!("can't monomorphize a {:?}",
+                                           map_node))
                 }
             }
         }
@@ -281,7 +281,7 @@ pub fn monomorphic_fn(ccx: @CrateContext,
         ast_map::NodeArg(..) |
         ast_map::NodeBlock(..) |
         ast_map::NodeLocal(..) => {
-            ccx.tcx.sess.bug(format!("can't monomorphize a {:?}", map_node))
+            ccx.sess().bug(format!("can't monomorphize a {:?}", map_node))
         }
     };
 
diff --git a/src/librustc/middle/trans/type_of.rs b/src/librustc/middle/trans/type_of.rs
index de3aff0fff6..f1130fced24 100644
--- a/src/librustc/middle/trans/type_of.rs
+++ b/src/librustc/middle/trans/type_of.rs
@@ -86,7 +86,7 @@ pub fn type_of_fn_from_ty(cx: &CrateContext, fty: ty::t) -> Type {
             }
         }
         _ => {
-            cx.sess.bug("type_of_fn_from_ty given non-closure, non-bare-fn")
+            cx.sess().bug("type_of_fn_from_ty given non-closure, non-bare-fn")
         }
     }
 }
@@ -142,7 +142,7 @@ pub fn sizing_type_of(cx: &CrateContext, t: ty::t) -> Type {
 
         ty::ty_unboxed_vec(mt) => {
             let sz_ty = sizing_type_of(cx, mt.ty);
-            Type::vec(cx.sess.targ_cfg.arch, &sz_ty)
+            Type::vec(cx.sess().targ_cfg.arch, &sz_ty)
         }
 
         ty::ty_tup(..) | ty::ty_enum(..) => {
@@ -162,7 +162,8 @@ pub fn sizing_type_of(cx: &CrateContext, t: ty::t) -> Type {
         }
 
         ty::ty_self(_) | ty::ty_infer(..) | ty::ty_param(..) | ty::ty_err(..) => {
-            cx.tcx.sess.bug(format!("fictitious type {:?} in sizing_type_of()", ty::get(t).sty))
+            cx.sess().bug(format!("fictitious type {:?} in sizing_type_of()",
+                                  ty::get(t).sty))
         }
     };
 
@@ -212,7 +213,7 @@ pub fn type_of(cx: &CrateContext, t: ty::t) -> Type {
       ty::ty_uint(t) => Type::uint_from_ty(cx, t),
       ty::ty_float(t) => Type::float_from_ty(t),
       ty::ty_str(ty::vstore_uniq) => {
-        Type::vec(cx.sess.targ_cfg.arch, &Type::i8()).ptr_to()
+        Type::vec(cx.sess().targ_cfg.arch, &Type::i8()).ptr_to()
       }
       ty::ty_enum(did, ref substs) => {
         // Only create the named struct, but don't fill it in. We
@@ -231,11 +232,11 @@ pub fn type_of(cx: &CrateContext, t: ty::t) -> Type {
       }
       ty::ty_vec(ref mt, ty::vstore_uniq) => {
           let ty = type_of(cx, mt.ty);
-          Type::vec(cx.sess.targ_cfg.arch, &ty).ptr_to()
+          Type::vec(cx.sess().targ_cfg.arch, &ty).ptr_to()
       }
       ty::ty_unboxed_vec(ref mt) => {
           let ty = type_of(cx, mt.ty);
-          Type::vec(cx.sess.targ_cfg.arch, &ty)
+          Type::vec(cx.sess().targ_cfg.arch, &ty)
       }
       ty::ty_ptr(ref mt) => type_of(cx, mt.ty).ptr_to(),
       ty::ty_rptr(_, ref mt) => type_of(cx, mt.ty).ptr_to(),
@@ -288,10 +289,10 @@ pub fn type_of(cx: &CrateContext, t: ty::t) -> Type {
               adt::incomplete_type_of(cx, repr, name)
           }
       }
-      ty::ty_self(..) => cx.tcx.sess.unimpl("type_of: ty_self"),
-      ty::ty_infer(..) => cx.tcx.sess.bug("type_of with ty_infer"),
-      ty::ty_param(..) => cx.tcx.sess.bug("type_of with ty_param"),
-      ty::ty_err(..) => cx.tcx.sess.bug("type_of with ty_err")
+      ty::ty_self(..) => cx.sess().unimpl("type_of: ty_self"),
+      ty::ty_infer(..) => cx.sess().bug("type_of with ty_infer"),
+      ty::ty_param(..) => cx.sess().bug("type_of with ty_param"),
+      ty::ty_err(..) => cx.sess().bug("type_of with ty_err")
     };
 
     debug!("--> mapped t={} {:?} to llty={}",
diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index e1dddda01f7..51787aedff8 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -11,7 +11,7 @@
 #[allow(non_camel_case_types)];
 
 use back::svh::Svh;
-use driver::session;
+use driver::session::Session;
 use metadata::csearch;
 use metadata;
 use middle::const_eval;
@@ -262,7 +262,7 @@ pub struct ctxt_ {
     interner: RefCell<FnvHashMap<intern_key, ~t_box_>>,
     next_id: Cell<uint>,
     cstore: @metadata::cstore::CStore,
-    sess: session::Session,
+    sess: Session,
     def_map: resolve::DefMap,
 
     named_region_map: @RefCell<resolve_lifetime::NamedRegionMap>,
@@ -1081,7 +1081,7 @@ pub type type_cache = RefCell<DefIdMap<ty_param_bounds_and_ty>>;
 
 pub type node_type_table = RefCell<HashMap<uint,t>>;
 
-pub fn mk_ctxt(s: session::Session,
+pub fn mk_ctxt(s: Session,
                dm: resolve::DefMap,
                named_region_map: @RefCell<resolve_lifetime::NamedRegionMap>,
                map: ast_map::Map,
diff --git a/src/librustc/middle/typeck/coherence.rs b/src/librustc/middle/typeck/coherence.rs
index ca5befa8d4e..1dfbc29b7f4 100644
--- a/src/librustc/middle/typeck/coherence.rs
+++ b/src/librustc/middle/typeck/coherence.rs
@@ -189,7 +189,7 @@ impl<'a> visit::Visitor<()> for PrivilegedScopeVisitor<'a> {
             ItemImpl(_, None, ast_ty, _) => {
                 if !self.cc.ast_type_is_defined_in_local_crate(ast_ty) {
                     // This is an error.
-                    let session = self.cc.crate_context.tcx.sess;
+                    let session = &self.cc.crate_context.tcx.sess;
                     session.span_err(item.span,
                                      "cannot associate methods with a type outside the \
                                      crate the type is defined in; define and implement \
@@ -210,7 +210,7 @@ impl<'a> visit::Visitor<()> for PrivilegedScopeVisitor<'a> {
                         self.cc.trait_ref_to_trait_def_id(trait_ref);
 
                     if trait_def_id.krate != LOCAL_CRATE {
-                        let session = self.cc.crate_context.tcx.sess;
+                        let session = &self.cc.crate_context.tcx.sess;
                         session.span_err(item.span,
                                 "cannot provide an extension implementation \
                                 where both trait and type are not defined in this crate");
@@ -274,7 +274,7 @@ impl CoherenceChecker {
                                        item.span,
                                        self_type.ty) {
                 None => {
-                    let session = self.crate_context.tcx.sess;
+                    let session = &self.crate_context.tcx.sess;
                     session.span_err(item.span,
                                      "no base type found for inherent implementation; \
                                       implement a trait or new type instead");
@@ -447,7 +447,7 @@ impl CoherenceChecker {
                             implementation_b);
 
                     if self.polytypes_unify(polytype_a.clone(), polytype_b) {
-                        let session = self.crate_context.tcx.sess;
+                        let session = &self.crate_context.tcx.sess;
                         session.span_err(
                             self.span_of_impl(implementation_a),
                             format!("conflicting implementations for trait `{}`",
diff --git a/src/librustdoc/clean.rs b/src/librustdoc/clean.rs
index c27725fd585..858a7ae1263 100644
--- a/src/librustdoc/clean.rs
+++ b/src/librustdoc/clean.rs
@@ -26,6 +26,7 @@ use rustc::metadata::decoder;
 
 use std;
 
+use core;
 use doctree;
 use visit_ast;
 use std::local_data;
@@ -84,7 +85,7 @@ impl<'a> Clean<Crate> for visit_ast::RustdocVisitor<'a> {
         let cx = local_data::get(super::ctxtkey, |x| *x.unwrap());
 
         let mut externs = ~[];
-        cx.sess.cstore.iter_crate_data(|n, meta| {
+        cx.sess().cstore.iter_crate_data(|n, meta| {
             externs.push((n, meta.clean()));
         });
 
@@ -683,7 +684,7 @@ impl Clean<Type> for ast::Ty {
     fn clean(&self) -> Type {
         use syntax::ast::*;
         debug!("cleaning type `{:?}`", self);
-        let codemap = local_data::get(super::ctxtkey, |x| *x.unwrap()).sess.codemap;
+        let codemap = local_data::get(super::ctxtkey, |x| *x.unwrap()).sess().codemap;
         debug!("span corresponds to `{}`", codemap.span_to_str(self.span));
         match self.node {
             TyNil => Unit,
@@ -865,7 +866,7 @@ pub struct Span {
 
 impl Clean<Span> for syntax::codemap::Span {
     fn clean(&self) -> Span {
-        let cm = local_data::get(super::ctxtkey, |x| *x.unwrap()).sess.codemap;
+        let cm = local_data::get(super::ctxtkey, |x| *x.unwrap()).sess().codemap;
         let filename = cm.span_to_filename(*self);
         let lo = cm.lookup_char_pos(self.lo);
         let hi = cm.lookup_char_pos(self.hi);
@@ -1179,7 +1180,7 @@ trait ToSource {
 impl ToSource for syntax::codemap::Span {
     fn to_src(&self) -> ~str {
         debug!("converting span {:?} to snippet", self.clean());
-        let cm = local_data::get(super::ctxtkey, |x| x.unwrap().clone()).sess.codemap.clone();
+        let cm = local_data::get(super::ctxtkey, |x| x.unwrap().clone()).sess().codemap.clone();
         let sn = match cm.span_to_snippet(*self) {
             Some(x) => x,
             None    => ~""
@@ -1234,10 +1235,10 @@ fn name_from_pat(p: &ast::Pat) -> ~str {
 fn resolve_type(path: Path, tpbs: Option<~[TyParamBound]>,
                 id: ast::NodeId) -> Type {
     let cx = local_data::get(super::ctxtkey, |x| *x.unwrap());
-    let tycx = match cx.tycx {
-        Some(tycx) => tycx,
+    let tycx = match cx.maybe_typed {
+        core::Typed(ref tycx) => tycx,
         // If we're extracting tests, this return value doesn't matter.
-        None => return Bool
+        core::NotTyped(_) => return Bool
     };
     debug!("searching for {:?} in defmap", id);
     let def_map = tycx.def_map.borrow();
@@ -1289,12 +1290,12 @@ fn resolve_use_source(path: Path, id: ast::NodeId) -> ImportSource {
 
 fn resolve_def(id: ast::NodeId) -> Option<ast::DefId> {
     let cx = local_data::get(super::ctxtkey, |x| *x.unwrap());
-    match cx.tycx {
-        Some(tcx) => {
+    match cx.maybe_typed {
+        core::Typed(ref tcx) => {
             let def_map = tcx.def_map.borrow();
             def_map.get().find(&id).map(|&d| ast_util::def_id_of_def(d))
         }
-        None => None
+        core::NotTyped(_) => None
     }
 }
 
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index eda24fb6dc2..41b46f2a3a4 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -27,10 +27,23 @@ use visit_ast::RustdocVisitor;
 use clean;
 use clean::Clean;
 
+pub enum MaybeTyped {
+    Typed(middle::ty::ctxt),
+    NotTyped(driver::session::Session)
+}
+
 pub struct DocContext {
     krate: ast::Crate,
-    tycx: Option<middle::ty::ctxt>,
-    sess: driver::session::Session
+    maybe_typed: MaybeTyped
+}
+
+impl DocContext {
+    pub fn sess<'a>(&'a self) -> &'a driver::session::Session {
+        match self.maybe_typed {
+            Typed(ref tcx) => &tcx.sess,
+            NotTyped(ref sess) => sess
+        }
+    }
 }
 
 pub struct CrateAnalysis {
@@ -67,27 +80,27 @@ fn get_ast_and_resolve(cpath: &Path,
                                               parsesess.cm,
                                               span_diagnostic_handler);
 
-    let mut cfg = build_configuration(sess);
+    let mut cfg = build_configuration(&sess);
     for cfg_ in cfgs.move_iter() {
         let cfg_ = token::intern_and_get_ident(cfg_);
         cfg.push(@dummy_spanned(ast::MetaWord(cfg_)));
     }
 
-    let krate = phase_1_parse_input(sess, cfg, &input);
-    let loader = &mut Loader::new(sess);
-    let id = from_str("rustdoc").unwrap();
-    let (krate, ast_map) = phase_2_configure_and_expand(sess, loader,
-                                                        krate, &id);
+    let krate = phase_1_parse_input(&sess, cfg, &input);
+    let (krate, ast_map) = phase_2_configure_and_expand(&sess, &mut Loader::new(sess),
+                                                        krate, &from_str("rustdoc").unwrap());
     let driver::driver::CrateAnalysis {
         exported_items, public_items, ty_cx, ..
     } = phase_3_run_analysis_passes(sess, &krate, ast_map);
 
     debug!("crate: {:?}", krate);
-    return (DocContext { krate: krate, tycx: Some(ty_cx), sess: sess },
-            CrateAnalysis {
-                exported_items: exported_items,
-                public_items: public_items,
-            });
+    (DocContext {
+        krate: krate,
+        maybe_typed: Typed(ty_cx)
+    }, CrateAnalysis {
+        exported_items: exported_items,
+        public_items: public_items,
+    })
 }
 
 pub fn run_core (libs: HashSet<Path>, cfgs: ~[~str], path: &Path) -> (clean::Crate, CrateAnalysis) {
diff --git a/src/librustdoc/test.rs b/src/librustdoc/test.rs
index d8b7c525538..ac87a4af483 100644
--- a/src/librustdoc/test.rs
+++ b/src/librustdoc/test.rs
@@ -58,17 +58,14 @@ pub fn run(input: &str, libs: @RefCell<HashSet<Path>>, mut test_args: ~[~str]) -
                                       parsesess.cm,
                                       span_diagnostic_handler);
 
-    let cfg = driver::build_configuration(sess);
-    let krate = driver::phase_1_parse_input(sess, cfg, &input);
-    let loader = &mut Loader::new(sess);
-    let id = from_str("rustdoc-test").unwrap();
-    let (krate, _) = driver::phase_2_configure_and_expand(sess, loader, krate,
-                                                          &id);
+    let cfg = driver::build_configuration(&sess);
+    let krate = driver::phase_1_parse_input(&sess, cfg, &input);
+    let (krate, _) = driver::phase_2_configure_and_expand(sess, &mut Loader::new(sess), krate,
+                                                          &from_str("rustdoc-test").unwrap());
 
     let ctx = @core::DocContext {
         krate: krate,
-        tycx: None,
-        sess: sess,
+        maybe_typed: core::NotTyped(sess),
     };
     local_data::set(super::ctxtkey, ctx);
 
@@ -140,7 +137,7 @@ fn runtest(test: &str, cratename: &str, libs: HashSet<Path>, should_fail: bool,
 
     let outdir = TempDir::new("rustdoctest").expect("rustdoc needs a tempdir");
     let out = Some(outdir.path().clone());
-    let cfg = driver::build_configuration(sess);
+    let cfg = driver::build_configuration(&sess);
     driver::compile_input(sess, cfg, &input, &out, &None);
 
     if no_run { return }
diff --git a/src/librustdoc/visit_ast.rs b/src/librustdoc/visit_ast.rs
index 5ac623af37a..c0a39112b69 100644
--- a/src/librustdoc/visit_ast.rs
+++ b/src/librustdoc/visit_ast.rs
@@ -183,21 +183,18 @@ impl<'a> RustdocVisitor<'a> {
 
     fn resolve_id(&mut self, id: ast::NodeId, glob: bool,
                   om: &mut Module) -> bool {
-        let def = {
-            let dm = match self.cx.tycx {
-                Some(tcx) => tcx.def_map.borrow(),
-                None => return false,
-            };
-            ast_util::def_id_of_def(*dm.get().get(&id))
+        let tcx = match self.cx.maybe_typed {
+            core::Typed(ref tcx) => tcx,
+            core::NotTyped(_) => return false
         };
+        let def = ast_util::def_id_of_def(*tcx.def_map.borrow().get().get(&id));
         if !ast_util::is_local(def) { return false }
         let analysis = match self.analysis {
             Some(analysis) => analysis, None => return false
         };
         if analysis.public_items.contains(&def.node) { return false }
 
-        let item = self.cx.tycx.unwrap().map.get(def.node);
-        match item {
+        match tcx.map.get(def.node) {
             ast_map::NodeItem(it) => {
                 if glob {
                     match it.node {