diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index 512d4d8c5b7..71c1c61e3d9 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -303,6 +303,19 @@ def default_build_triple():
     return "{}-{}".format(cputype, ostype)
 
 
+@contextlib.contextmanager
+def output(filepath):
+    tmp = filepath + '.tmp'
+    with open(tmp, 'w') as f:
+        yield f
+    try:
+        os.remove(filepath)  # PermissionError/OSError on Win32 if in use
+        os.rename(tmp, filepath)
+    except OSError:
+        shutil.copy2(tmp, filepath)
+        os.remove(tmp)
+
+
 class RustBuild(object):
     """Provide all the methods required to build Rust"""
     def __init__(self):
@@ -346,7 +359,7 @@ class RustBuild(object):
             self._download_stage0_helper(filename, "rustc")
             self.fix_executable("{}/bin/rustc".format(self.bin_root()))
             self.fix_executable("{}/bin/rustdoc".format(self.bin_root()))
-            with open(self.rustc_stamp(), 'w') as rust_stamp:
+            with output(self.rustc_stamp()) as rust_stamp:
                 rust_stamp.write(self.date)
 
             # This is required so that we don't mix incompatible MinGW
@@ -363,7 +376,7 @@ class RustBuild(object):
             filename = "cargo-{}-{}.tar.gz".format(cargo_channel, self.build)
             self._download_stage0_helper(filename, "cargo")
             self.fix_executable("{}/bin/cargo".format(self.bin_root()))
-            with open(self.cargo_stamp(), 'w') as cargo_stamp:
+            with output(self.cargo_stamp()) as cargo_stamp:
                 cargo_stamp.write(self.date)
 
     def _download_stage0_helper(self, filename, pattern):
@@ -776,7 +789,7 @@ def bootstrap(help_triggered):
     if build.use_vendored_sources:
         if not os.path.exists('.cargo'):
             os.makedirs('.cargo')
-        with open('.cargo/config', 'w') as cargo_config:
+        with output('.cargo/config') as cargo_config:
             cargo_config.write("""
                 [source.crates-io]
                 replace-with = 'vendored-sources'
diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index 6c3a476d084..eb534cb685e 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -44,7 +44,7 @@ pub struct Builder<'a> {
     pub top_stage: u32,
     pub kind: Kind,
     cache: Cache,
-    stack: RefCell<Vec<Box<Any>>>,
+    stack: RefCell<Vec<Box<dyn Any>>>,
     time_spent_on_dependencies: Cell<Duration>,
     pub paths: Vec<PathBuf>,
     graph_nodes: RefCell<HashMap<String, NodeIndex>>,
diff --git a/src/bootstrap/cache.rs b/src/bootstrap/cache.rs
index d81c6bc28e5..bca5ff85ba2 100644
--- a/src/bootstrap/cache.rs
+++ b/src/bootstrap/cache.rs
@@ -249,7 +249,7 @@ lazy_static! {
 pub struct Cache(
     RefCell<HashMap<
         TypeId,
-        Box<Any>, // actually a HashMap<Step, Interned<Step::Output>>
+        Box<dyn Any>, // actually a HashMap<Step, Interned<Step::Output>>
     >>
 );
 
diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index 298bd58c6cd..7d94bac66f7 100644
--- a/src/bootstrap/compile.rs
+++ b/src/bootstrap/compile.rs
@@ -1189,7 +1189,7 @@ pub fn run_cargo(builder: &Builder, cargo: &mut Command, stamp: &Path, is_check:
 pub fn stream_cargo(
     builder: &Builder,
     cargo: &mut Command,
-    cb: &mut FnMut(CargoMessage),
+    cb: &mut dyn FnMut(CargoMessage),
 ) -> bool {
     if builder.config.dry_run {
         return true;
diff --git a/src/bootstrap/configure.py b/src/bootstrap/configure.py
index 80fa96509bd..9fdba044f4b 100755
--- a/src/bootstrap/configure.py
+++ b/src/bootstrap/configure.py
@@ -432,7 +432,7 @@ for section_key in config:
 # order that we read it in.
 p("")
 p("writing `config.toml` in current directory")
-with open('config.toml', 'w') as f:
+with bootstrap.output('config.toml') as f:
     for section in section_order:
         if section == 'target':
             for target in targets:
@@ -442,7 +442,7 @@ with open('config.toml', 'w') as f:
             for line in sections[section]:
                 f.write(line + "\n")
 
-with open('Makefile', 'w') as f:
+with bootstrap.output('Makefile') as f:
     contents = os.path.join(rust_dir, 'src', 'bootstrap', 'mk', 'Makefile.in')
     contents = open(contents).read()
     contents = contents.replace("$(CFG_SRC_DIR)", rust_dir + '/')
diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index 5f66d0b102e..cd9a639e82e 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -113,6 +113,7 @@
 //! More documentation can be found in each respective module below, and you can
 //! also check out the `src/bootstrap/README.md` file for more information.
 
+#![deny(bare_trait_objects)]
 #![deny(warnings)]
 #![feature(core_intrinsics)]
 #![feature(drain_filter)]
@@ -1174,13 +1175,13 @@ impl Build {
     /// Copies the `src` directory recursively to `dst`. Both are assumed to exist
     /// when this function is called. Unwanted files or directories can be skipped
     /// by returning `false` from the filter function.
-    pub fn cp_filtered(&self, src: &Path, dst: &Path, filter: &Fn(&Path) -> bool) {
+    pub fn cp_filtered(&self, src: &Path, dst: &Path, filter: &dyn Fn(&Path) -> bool) {
         // Immediately recurse with an empty relative path
         self.recurse_(src, dst, Path::new(""), filter)
     }
 
     // Inner function does the actual work
-    fn recurse_(&self, src: &Path, dst: &Path, relative: &Path, filter: &Fn(&Path) -> bool) {
+    fn recurse_(&self, src: &Path, dst: &Path, relative: &Path, filter: &dyn Fn(&Path) -> bool) {
         for f in self.read_dir(src) {
             let path = f.path();
             let name = path.file_name().unwrap();
diff --git a/src/libcore/num/flt2dec/strategy/dragon.rs b/src/libcore/num/flt2dec/strategy/dragon.rs
index 9c9e531c593..aa6a08cb205 100644
--- a/src/libcore/num/flt2dec/strategy/dragon.rs
+++ b/src/libcore/num/flt2dec/strategy/dragon.rs
@@ -8,12 +8,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-/*!
-Almost direct (but slightly optimized) Rust translation of Figure 3 of \[1\].
-
-\[1\] Burger, R. G. and Dybvig, R. K. 1996. Printing floating-point numbers
-    quickly and accurately. SIGPLAN Not. 31, 5 (May. 1996), 108-116.
-*/
+//! Almost direct (but slightly optimized) Rust translation of Figure 3 of "Printing
+//! Floating-Point Numbers Quickly and Accurately"[^1].
+//!
+//! [^1]: Burger, R. G. and Dybvig, R. K. 1996. Printing floating-point numbers
+//!   quickly and accurately. SIGPLAN Not. 31, 5 (May. 1996), 108-116.
 
 use cmp::Ordering;
 
diff --git a/src/libcore/num/flt2dec/strategy/grisu.rs b/src/libcore/num/flt2dec/strategy/grisu.rs
index 5c023a191db..f33186e59c2 100644
--- a/src/libcore/num/flt2dec/strategy/grisu.rs
+++ b/src/libcore/num/flt2dec/strategy/grisu.rs
@@ -8,13 +8,12 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-/*!
-Rust adaptation of Grisu3 algorithm described in \[1\]. It uses about
-1KB of precomputed table, and in turn, it's very quick for most inputs.
-
-\[1\] Florian Loitsch. 2010. Printing floating-point numbers quickly and
-    accurately with integers. SIGPLAN Not. 45, 6 (June 2010), 233-243.
-*/
+//! Rust adaptation of the Grisu3 algorithm described in "Printing Floating-Point Numbers Quickly
+//! and Accurately with Integers"[^1]. It uses about 1KB of precomputed table, and in turn, it's
+//! very quick for most inputs.
+//!
+//! [^1]: Florian Loitsch. 2010. Printing floating-point numbers quickly and
+//!   accurately with integers. SIGPLAN Not. 45, 6 (June 2010), 233-243.
 
 use num::diy_float::Fp;
 use num::flt2dec::{Decoded, MAX_SIG_DIGITS, round_up};
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index 8a47b8ea648..aed70861e33 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![deny(bare_trait_objects)]
+
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
       html_root_url = "https://doc.rust-lang.org/nightly/")]
@@ -1292,7 +1294,7 @@ impl PrimitiveTypeTable {
 /// This is the visitor that walks the whole crate.
 pub struct Resolver<'a> {
     session: &'a Session,
-    cstore: &'a CrateStore,
+    cstore: &'a dyn CrateStore,
 
     pub definitions: Definitions,
 
@@ -1388,7 +1390,7 @@ pub struct Resolver<'a> {
     /// true if `#![feature(use_extern_macros)]`
     use_extern_macros: bool,
 
-    crate_loader: &'a mut CrateLoader,
+    crate_loader: &'a mut dyn CrateLoader,
     macro_names: FxHashSet<Ident>,
     global_macros: FxHashMap<Name, &'a NameBinding<'a>>,
     pub all_macros: FxHashMap<Name, Def>,
@@ -1604,11 +1606,11 @@ impl<'a> Resolver<'a> {
 
 impl<'a> Resolver<'a> {
     pub fn new(session: &'a Session,
-               cstore: &'a CrateStore,
+               cstore: &'a dyn CrateStore,
                krate: &Crate,
                crate_name: &str,
                make_glob_map: MakeGlobMap,
-               crate_loader: &'a mut CrateLoader,
+               crate_loader: &'a mut dyn CrateLoader,
                arenas: &'a ResolverArenas<'a>)
                -> Resolver<'a> {
         let root_def_id = DefId::local(CRATE_DEF_INDEX);
diff --git a/src/libstd/env.rs b/src/libstd/env.rs
index c0e1e2533a0..9066c0b7694 100644
--- a/src/libstd/env.rs
+++ b/src/libstd/env.rs
@@ -541,7 +541,7 @@ impl Error for JoinPathsError {
 /// ```
 #[rustc_deprecated(since = "1.29.0",
     reason = "This function's behavior is unexpected and probably not what you want. \
-              Consider using the home_dir function from crates.io/crates/dirs instead.")]
+              Consider using the home_dir function from https://crates.io/crates/dirs instead.")]
 #[stable(feature = "env", since = "1.0.0")]
 pub fn home_dir() -> Option<PathBuf> {
     os_imp::home_dir()
diff --git a/src/libstd/ffi/c_str.rs b/src/libstd/ffi/c_str.rs
index 6513d11dd51..b816f4b7850 100644
--- a/src/libstd/ffi/c_str.rs
+++ b/src/libstd/ffi/c_str.rs
@@ -706,6 +706,14 @@ impl From<Box<CStr>> for CString {
     }
 }
 
+#[stable(feature = "more_box_slice_clone", since = "1.29.0")]
+impl Clone for Box<CStr> {
+    #[inline]
+    fn clone(&self) -> Self {
+        (**self).into()
+    }
+}
+
 #[stable(feature = "box_from_c_string", since = "1.20.0")]
 impl From<CString> for Box<CStr> {
     #[inline]
diff --git a/src/libstd/ffi/os_str.rs b/src/libstd/ffi/os_str.rs
index 4ada6a77a8e..b1c6e7af693 100644
--- a/src/libstd/ffi/os_str.rs
+++ b/src/libstd/ffi/os_str.rs
@@ -642,6 +642,14 @@ impl From<OsString> for Box<OsStr> {
     }
 }
 
+#[stable(feature = "more_box_slice_clone", since = "1.29.0")]
+impl Clone for Box<OsStr> {
+    #[inline]
+    fn clone(&self) -> Self {
+        self.to_os_string().into_boxed_os_str()
+    }
+}
+
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<OsString> for Arc<OsStr> {
     #[inline]
diff --git a/src/libstd/path.rs b/src/libstd/path.rs
index 3dc1e9c3dad..2d868629278 100644
--- a/src/libstd/path.rs
+++ b/src/libstd/path.rs
@@ -1410,6 +1410,14 @@ impl From<PathBuf> for Box<Path> {
     }
 }
 
+#[stable(feature = "more_box_slice_clone", since = "1.29.0")]
+impl Clone for Box<Path> {
+    #[inline]
+    fn clone(&self) -> Self {
+        self.to_path_buf().into_boxed_path()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T: ?Sized + AsRef<OsStr>> From<&'a T> for PathBuf {
     fn from(s: &'a T) -> PathBuf {
diff --git a/src/libstd/sync/mpsc/mod.rs b/src/libstd/sync/mpsc/mod.rs
index 2dd3aebe610..cbda5afadcd 100644
--- a/src/libstd/sync/mpsc/mod.rs
+++ b/src/libstd/sync/mpsc/mod.rs
@@ -689,7 +689,7 @@ impl<T> UnsafeFlavor<T> for Receiver<T> {
 /// only one [`Receiver`] is supported.
 ///
 /// If the [`Receiver`] is disconnected while trying to [`send`] with the
-/// [`Sender`], the [`send`] method will return a [`SendError`]. Similarly, If the
+/// [`Sender`], the [`send`] method will return a [`SendError`]. Similarly, if the
 /// [`Sender`] is disconnected while trying to [`recv`], the [`recv`] method will
 /// return a [`RecvError`].
 ///
diff --git a/src/libsyntax_ext/asm.rs b/src/libsyntax_ext/asm.rs
index dd8f79d20ab..4ebb1fcb653 100644
--- a/src/libsyntax_ext/asm.rs
+++ b/src/libsyntax_ext/asm.rs
@@ -50,7 +50,7 @@ const OPTIONS: &'static [&'static str] = &["volatile", "alignstack", "intel"];
 pub fn expand_asm<'cx>(cx: &'cx mut ExtCtxt,
                        sp: Span,
                        tts: &[tokenstream::TokenTree])
-                       -> Box<base::MacResult + 'cx> {
+                       -> Box<dyn base::MacResult + 'cx> {
     if !cx.ecfg.enable_asm() {
         feature_gate::emit_feature_err(&cx.parse_sess,
                                        "asm",
diff --git a/src/libsyntax_ext/assert.rs b/src/libsyntax_ext/assert.rs
index fe4d599d824..8d0a04831fc 100644
--- a/src/libsyntax_ext/assert.rs
+++ b/src/libsyntax_ext/assert.rs
@@ -22,7 +22,7 @@ pub fn expand_assert<'cx>(
     cx: &'cx mut ExtCtxt,
     sp: Span,
     tts: &[TokenTree],
-) -> Box<MacResult + 'cx> {
+) -> Box<dyn MacResult + 'cx> {
     let mut parser = cx.new_parser_from_tts(tts);
     let cond_expr = panictry!(parser.parse_expr());
     let custom_msg_args = if parser.eat(&token::Comma) {
diff --git a/src/libsyntax_ext/cfg.rs b/src/libsyntax_ext/cfg.rs
index 6acc578d07e..2384b6a796e 100644
--- a/src/libsyntax_ext/cfg.rs
+++ b/src/libsyntax_ext/cfg.rs
@@ -23,7 +23,7 @@ use syntax_pos::Span;
 pub fn expand_cfg<'cx>(cx: &mut ExtCtxt,
                        sp: Span,
                        tts: &[tokenstream::TokenTree])
-                       -> Box<base::MacResult + 'static> {
+                       -> Box<dyn base::MacResult + 'static> {
     let sp = sp.apply_mark(cx.current_expansion.mark);
     let mut p = cx.new_parser_from_tts(tts);
     let cfg = panictry!(p.parse_meta_item());
diff --git a/src/libsyntax_ext/compile_error.rs b/src/libsyntax_ext/compile_error.rs
index 7bc7afba63c..ce7fb400bd5 100644
--- a/src/libsyntax_ext/compile_error.rs
+++ b/src/libsyntax_ext/compile_error.rs
@@ -18,7 +18,7 @@ use syntax::tokenstream;
 pub fn expand_compile_error<'cx>(cx: &'cx mut ExtCtxt,
                               sp: Span,
                               tts: &[tokenstream::TokenTree])
-                              -> Box<base::MacResult + 'cx> {
+                              -> Box<dyn base::MacResult + 'cx> {
     let var = match get_single_str_from_tts(cx, sp, tts, "compile_error!") {
         None => return DummyResult::expr(sp),
         Some(v) => v,
diff --git a/src/libsyntax_ext/concat.rs b/src/libsyntax_ext/concat.rs
index 1c6f0089503..69b4a83764e 100644
--- a/src/libsyntax_ext/concat.rs
+++ b/src/libsyntax_ext/concat.rs
@@ -21,7 +21,7 @@ pub fn expand_syntax_ext(
     cx: &mut base::ExtCtxt,
     sp: syntax_pos::Span,
     tts: &[tokenstream::TokenTree],
-) -> Box<base::MacResult + 'static> {
+) -> Box<dyn base::MacResult + 'static> {
     let es = match base::get_exprs_from_tts(cx, sp, tts) {
         Some(e) => e,
         None => return base::DummyResult::expr(sp),
diff --git a/src/libsyntax_ext/concat_idents.rs b/src/libsyntax_ext/concat_idents.rs
index 828c2470841..a3c5c3df66e 100644
--- a/src/libsyntax_ext/concat_idents.rs
+++ b/src/libsyntax_ext/concat_idents.rs
@@ -21,7 +21,7 @@ use syntax::tokenstream::TokenTree;
 pub fn expand_syntax_ext<'cx>(cx: &'cx mut ExtCtxt,
                               sp: Span,
                               tts: &[TokenTree])
-                              -> Box<base::MacResult + 'cx> {
+                              -> Box<dyn base::MacResult + 'cx> {
     if !cx.ecfg.enable_concat_idents() {
         feature_gate::emit_feature_err(&cx.parse_sess,
                                        "concat_idents",
diff --git a/src/libsyntax_ext/deriving/bounds.rs b/src/libsyntax_ext/deriving/bounds.rs
index 7f03001d9c6..41e980b3346 100644
--- a/src/libsyntax_ext/deriving/bounds.rs
+++ b/src/libsyntax_ext/deriving/bounds.rs
@@ -19,7 +19,7 @@ pub fn expand_deriving_unsafe_bound(cx: &mut ExtCtxt,
                                     span: Span,
                                     _: &MetaItem,
                                     _: &Annotatable,
-                                    _: &mut FnMut(Annotatable)) {
+                                    _: &mut dyn FnMut(Annotatable)) {
     cx.span_err(span, "this unsafe trait should be implemented explicitly");
 }
 
@@ -27,7 +27,7 @@ pub fn expand_deriving_copy(cx: &mut ExtCtxt,
                             span: Span,
                             mitem: &MetaItem,
                             item: &Annotatable,
-                            push: &mut FnMut(Annotatable)) {
+                            push: &mut dyn FnMut(Annotatable)) {
     let trait_def = TraitDef {
         span,
         attributes: Vec::new(),
diff --git a/src/libsyntax_ext/deriving/clone.rs b/src/libsyntax_ext/deriving/clone.rs
index 9aeac5b1ddb..ec935b3e72f 100644
--- a/src/libsyntax_ext/deriving/clone.rs
+++ b/src/libsyntax_ext/deriving/clone.rs
@@ -25,7 +25,7 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt,
                              span: Span,
                              mitem: &MetaItem,
                              item: &Annotatable,
-                             push: &mut FnMut(Annotatable)) {
+                             push: &mut dyn FnMut(Annotatable)) {
     // check if we can use a short form
     //
     // the short form is `fn clone(&self) -> Self { *self }`
diff --git a/src/libsyntax_ext/deriving/cmp/eq.rs b/src/libsyntax_ext/deriving/cmp/eq.rs
index 00ab39032ac..f202bc4e524 100644
--- a/src/libsyntax_ext/deriving/cmp/eq.rs
+++ b/src/libsyntax_ext/deriving/cmp/eq.rs
@@ -23,7 +23,7 @@ pub fn expand_deriving_eq(cx: &mut ExtCtxt,
                           span: Span,
                           mitem: &MetaItem,
                           item: &Annotatable,
-                          push: &mut FnMut(Annotatable)) {
+                          push: &mut dyn FnMut(Annotatable)) {
     let inline = cx.meta_word(span, Symbol::intern("inline"));
     let hidden = cx.meta_list_item_word(span, Symbol::intern("hidden"));
     let doc = cx.meta_list(span, Symbol::intern("doc"), vec![hidden]);
diff --git a/src/libsyntax_ext/deriving/cmp/ord.rs b/src/libsyntax_ext/deriving/cmp/ord.rs
index 99b6f752e94..117bedf453e 100644
--- a/src/libsyntax_ext/deriving/cmp/ord.rs
+++ b/src/libsyntax_ext/deriving/cmp/ord.rs
@@ -23,7 +23,7 @@ pub fn expand_deriving_ord(cx: &mut ExtCtxt,
                            span: Span,
                            mitem: &MetaItem,
                            item: &Annotatable,
-                           push: &mut FnMut(Annotatable)) {
+                           push: &mut dyn FnMut(Annotatable)) {
     let inline = cx.meta_word(span, Symbol::intern("inline"));
     let attrs = vec![cx.attribute(span, inline)];
     let trait_def = TraitDef {
diff --git a/src/libsyntax_ext/deriving/cmp/partial_eq.rs b/src/libsyntax_ext/deriving/cmp/partial_eq.rs
index c259733d81a..24a3a7542fb 100644
--- a/src/libsyntax_ext/deriving/cmp/partial_eq.rs
+++ b/src/libsyntax_ext/deriving/cmp/partial_eq.rs
@@ -23,7 +23,7 @@ pub fn expand_deriving_partial_eq(cx: &mut ExtCtxt,
                                   span: Span,
                                   mitem: &MetaItem,
                                   item: &Annotatable,
-                                  push: &mut FnMut(Annotatable)) {
+                                  push: &mut dyn FnMut(Annotatable)) {
     // structures are equal if all fields are equal, and non equal, if
     // any fields are not equal or if the enum variants are different
     fn cs_op(cx: &mut ExtCtxt,
diff --git a/src/libsyntax_ext/deriving/cmp/partial_ord.rs b/src/libsyntax_ext/deriving/cmp/partial_ord.rs
index 2b3930063f3..3705a245584 100644
--- a/src/libsyntax_ext/deriving/cmp/partial_ord.rs
+++ b/src/libsyntax_ext/deriving/cmp/partial_ord.rs
@@ -25,7 +25,7 @@ pub fn expand_deriving_partial_ord(cx: &mut ExtCtxt,
                                    span: Span,
                                    mitem: &MetaItem,
                                    item: &Annotatable,
-                                   push: &mut FnMut(Annotatable)) {
+                                   push: &mut dyn FnMut(Annotatable)) {
     macro_rules! md {
         ($name:expr, $op:expr, $equal:expr) => { {
             let inline = cx.meta_word(span, Symbol::intern("inline"));
diff --git a/src/libsyntax_ext/deriving/debug.rs b/src/libsyntax_ext/deriving/debug.rs
index b546f5df157..c2a7dea3316 100644
--- a/src/libsyntax_ext/deriving/debug.rs
+++ b/src/libsyntax_ext/deriving/debug.rs
@@ -23,7 +23,7 @@ pub fn expand_deriving_debug(cx: &mut ExtCtxt,
                              span: Span,
                              mitem: &MetaItem,
                              item: &Annotatable,
-                             push: &mut FnMut(Annotatable)) {
+                             push: &mut dyn FnMut(Annotatable)) {
     // &mut ::std::fmt::Formatter
     let fmtr = Ptr(Box::new(Literal(path_std!(cx, fmt::Formatter))),
                    Borrowed(None, ast::Mutability::Mutable));
diff --git a/src/libsyntax_ext/deriving/decodable.rs b/src/libsyntax_ext/deriving/decodable.rs
index 7618fe63ab3..1e04d8fa22a 100644
--- a/src/libsyntax_ext/deriving/decodable.rs
+++ b/src/libsyntax_ext/deriving/decodable.rs
@@ -27,7 +27,7 @@ pub fn expand_deriving_rustc_decodable(cx: &mut ExtCtxt,
                                        span: Span,
                                        mitem: &MetaItem,
                                        item: &Annotatable,
-                                       push: &mut FnMut(Annotatable)) {
+                                       push: &mut dyn FnMut(Annotatable)) {
     expand_deriving_decodable_imp(cx, span, mitem, item, push, "rustc_serialize")
 }
 
@@ -35,7 +35,7 @@ pub fn expand_deriving_decodable(cx: &mut ExtCtxt,
                                  span: Span,
                                  mitem: &MetaItem,
                                  item: &Annotatable,
-                                 push: &mut FnMut(Annotatable)) {
+                                 push: &mut dyn FnMut(Annotatable)) {
     warn_if_deprecated(cx, span, "Decodable");
     expand_deriving_decodable_imp(cx, span, mitem, item, push, "serialize")
 }
@@ -44,7 +44,7 @@ fn expand_deriving_decodable_imp(cx: &mut ExtCtxt,
                                  span: Span,
                                  mitem: &MetaItem,
                                  item: &Annotatable,
-                                 push: &mut FnMut(Annotatable),
+                                 push: &mut dyn FnMut(Annotatable),
                                  krate: &'static str) {
     let typaram = &*deriving::hygienic_type_parameter(item, "__D");
 
diff --git a/src/libsyntax_ext/deriving/default.rs b/src/libsyntax_ext/deriving/default.rs
index cbd6a257b77..958116f7809 100644
--- a/src/libsyntax_ext/deriving/default.rs
+++ b/src/libsyntax_ext/deriving/default.rs
@@ -23,7 +23,7 @@ pub fn expand_deriving_default(cx: &mut ExtCtxt,
                                span: Span,
                                mitem: &MetaItem,
                                item: &Annotatable,
-                               push: &mut FnMut(Annotatable)) {
+                               push: &mut dyn FnMut(Annotatable)) {
     let inline = cx.meta_word(span, Symbol::intern("inline"));
     let attrs = vec![cx.attribute(span, inline)];
     let trait_def = TraitDef {
diff --git a/src/libsyntax_ext/deriving/encodable.rs b/src/libsyntax_ext/deriving/encodable.rs
index 8b409df1f09..5438c8b52af 100644
--- a/src/libsyntax_ext/deriving/encodable.rs
+++ b/src/libsyntax_ext/deriving/encodable.rs
@@ -108,7 +108,7 @@ pub fn expand_deriving_rustc_encodable(cx: &mut ExtCtxt,
                                        span: Span,
                                        mitem: &MetaItem,
                                        item: &Annotatable,
-                                       push: &mut FnMut(Annotatable)) {
+                                       push: &mut dyn FnMut(Annotatable)) {
     expand_deriving_encodable_imp(cx, span, mitem, item, push, "rustc_serialize")
 }
 
@@ -116,7 +116,7 @@ pub fn expand_deriving_encodable(cx: &mut ExtCtxt,
                                  span: Span,
                                  mitem: &MetaItem,
                                  item: &Annotatable,
-                                 push: &mut FnMut(Annotatable)) {
+                                 push: &mut dyn FnMut(Annotatable)) {
     warn_if_deprecated(cx, span, "Encodable");
     expand_deriving_encodable_imp(cx, span, mitem, item, push, "serialize")
 }
@@ -125,7 +125,7 @@ fn expand_deriving_encodable_imp(cx: &mut ExtCtxt,
                                  span: Span,
                                  mitem: &MetaItem,
                                  item: &Annotatable,
-                                 push: &mut FnMut(Annotatable),
+                                 push: &mut dyn FnMut(Annotatable),
                                  krate: &'static str) {
     let typaram = &*deriving::hygienic_type_parameter(item, "__S");
 
diff --git a/src/libsyntax_ext/deriving/generic/mod.rs b/src/libsyntax_ext/deriving/generic/mod.rs
index 3ea0eb8bbd8..aad69c109f9 100644
--- a/src/libsyntax_ext/deriving/generic/mod.rs
+++ b/src/libsyntax_ext/deriving/generic/mod.rs
@@ -330,7 +330,7 @@ pub enum SubstructureFields<'a> {
 /// Combine the values of all the fields together. The last argument is
 /// all the fields of all the structures.
 pub type CombineSubstructureFunc<'a> =
-    Box<FnMut(&mut ExtCtxt, Span, &Substructure) -> P<Expr> + 'a>;
+    Box<dyn FnMut(&mut ExtCtxt, Span, &Substructure) -> P<Expr> + 'a>;
 
 /// Deal with non-matching enum variants.  The tuple is a list of
 /// identifiers (one for each `Self` argument, which could be any of the
@@ -338,7 +338,7 @@ pub type CombineSubstructureFunc<'a> =
 /// holding the variant index value for each of the `Self` arguments.  The
 /// last argument is all the non-`Self` args of the method being derived.
 pub type EnumNonMatchCollapsedFunc<'a> =
-    Box<FnMut(&mut ExtCtxt, Span, (&[Ident], &[Ident]), &[P<Expr>]) -> P<Expr> + 'a>;
+    Box<dyn FnMut(&mut ExtCtxt, Span, (&[Ident], &[Ident]), &[P<Expr>]) -> P<Expr> + 'a>;
 
 pub fn combine_substructure<'a>(f: CombineSubstructureFunc<'a>)
                                 -> RefCell<CombineSubstructureFunc<'a>> {
@@ -398,7 +398,7 @@ impl<'a> TraitDef<'a> {
                   cx: &mut ExtCtxt,
                   mitem: &ast::MetaItem,
                   item: &'a Annotatable,
-                  push: &mut FnMut(Annotatable)) {
+                  push: &mut dyn FnMut(Annotatable)) {
         self.expand_ext(cx, mitem, item, push, false);
     }
 
@@ -406,7 +406,7 @@ impl<'a> TraitDef<'a> {
                       cx: &mut ExtCtxt,
                       mitem: &ast::MetaItem,
                       item: &'a Annotatable,
-                      push: &mut FnMut(Annotatable),
+                      push: &mut dyn FnMut(Annotatable),
                       from_scratch: bool) {
         match *item {
             Annotatable::Item(ref item) => {
diff --git a/src/libsyntax_ext/deriving/hash.rs b/src/libsyntax_ext/deriving/hash.rs
index 67096cdb49a..7d22998487b 100644
--- a/src/libsyntax_ext/deriving/hash.rs
+++ b/src/libsyntax_ext/deriving/hash.rs
@@ -22,7 +22,7 @@ pub fn expand_deriving_hash(cx: &mut ExtCtxt,
                             span: Span,
                             mitem: &MetaItem,
                             item: &Annotatable,
-                            push: &mut FnMut(Annotatable)) {
+                            push: &mut dyn FnMut(Annotatable)) {
 
     let path = Path::new_(pathvec_std!(cx, hash::Hash), None, vec![], PathKind::Std);
 
diff --git a/src/libsyntax_ext/deriving/mod.rs b/src/libsyntax_ext/deriving/mod.rs
index e6a1434ca9d..2f5e42d2f7b 100644
--- a/src/libsyntax_ext/deriving/mod.rs
+++ b/src/libsyntax_ext/deriving/mod.rs
@@ -72,7 +72,7 @@ macro_rules! derive_traits {
             }
         }
 
-        pub fn register_builtin_derives(resolver: &mut Resolver) {
+        pub fn register_builtin_derives(resolver: &mut dyn Resolver) {
             $(
                 resolver.add_builtin(
                     ast::Ident::with_empty_ctxt(Symbol::intern($name)),
diff --git a/src/libsyntax_ext/env.rs b/src/libsyntax_ext/env.rs
index bbc5b03d688..3c34bf496da 100644
--- a/src/libsyntax_ext/env.rs
+++ b/src/libsyntax_ext/env.rs
@@ -26,7 +26,7 @@ use std::env;
 pub fn expand_option_env<'cx>(cx: &'cx mut ExtCtxt,
                               sp: Span,
                               tts: &[tokenstream::TokenTree])
-                              -> Box<base::MacResult + 'cx> {
+                              -> Box<dyn base::MacResult + 'cx> {
     let var = match get_single_str_from_tts(cx, sp, tts, "option_env!") {
         None => return DummyResult::expr(sp),
         Some(v) => v,
@@ -57,7 +57,7 @@ pub fn expand_option_env<'cx>(cx: &'cx mut ExtCtxt,
 pub fn expand_env<'cx>(cx: &'cx mut ExtCtxt,
                        sp: Span,
                        tts: &[tokenstream::TokenTree])
-                       -> Box<base::MacResult + 'cx> {
+                       -> Box<dyn base::MacResult + 'cx> {
     let mut exprs = match get_exprs_from_tts(cx, sp, tts) {
         Some(ref exprs) if exprs.is_empty() => {
             cx.span_err(sp, "env! takes 1 or 2 arguments");
diff --git a/src/libsyntax_ext/format.rs b/src/libsyntax_ext/format.rs
index 4bf764b1101..8587d11b227 100644
--- a/src/libsyntax_ext/format.rs
+++ b/src/libsyntax_ext/format.rs
@@ -679,7 +679,7 @@ impl<'a, 'b> Context<'a, 'b> {
 pub fn expand_format_args<'cx>(ecx: &'cx mut ExtCtxt,
                                mut sp: Span,
                                tts: &[tokenstream::TokenTree])
-                               -> Box<base::MacResult + 'cx> {
+                               -> Box<dyn base::MacResult + 'cx> {
     sp = sp.apply_mark(ecx.current_expansion.mark);
     match parse_args(ecx, sp, tts) {
         Some((efmt, args, names)) => {
diff --git a/src/libsyntax_ext/global_asm.rs b/src/libsyntax_ext/global_asm.rs
index 642aa0e5b12..40ecd6e1519 100644
--- a/src/libsyntax_ext/global_asm.rs
+++ b/src/libsyntax_ext/global_asm.rs
@@ -34,7 +34,7 @@ pub const MACRO: &'static str = "global_asm";
 
 pub fn expand_global_asm<'cx>(cx: &'cx mut ExtCtxt,
                               sp: Span,
-                              tts: &[tokenstream::TokenTree]) -> Box<base::MacResult + 'cx> {
+                              tts: &[tokenstream::TokenTree]) -> Box<dyn base::MacResult + 'cx> {
     if !cx.ecfg.enable_global_asm() {
         feature_gate::emit_feature_err(&cx.parse_sess,
                                        MACRO,
diff --git a/src/libsyntax_ext/lib.rs b/src/libsyntax_ext/lib.rs
index 31125183266..bdf7a8d7040 100644
--- a/src/libsyntax_ext/lib.rs
+++ b/src/libsyntax_ext/lib.rs
@@ -10,6 +10,8 @@
 
 //! Syntax extensions in the Rust compiler.
 
+#![deny(bare_trait_objects)]
+
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/")]
@@ -59,7 +61,7 @@ use syntax::ext::base::{MacroExpanderFn, NormalTT, NamedSyntaxExtension};
 use syntax::ext::hygiene;
 use syntax::symbol::Symbol;
 
-pub fn register_builtins(resolver: &mut syntax::ext::base::Resolver,
+pub fn register_builtins(resolver: &mut dyn syntax::ext::base::Resolver,
                          user_exts: Vec<NamedSyntaxExtension>,
                          enable_quotes: bool) {
     deriving::register_builtin_derives(resolver);
diff --git a/src/libsyntax_ext/log_syntax.rs b/src/libsyntax_ext/log_syntax.rs
index 71f1951d5d4..7b76b1e8914 100644
--- a/src/libsyntax_ext/log_syntax.rs
+++ b/src/libsyntax_ext/log_syntax.rs
@@ -17,7 +17,7 @@ use syntax_pos;
 pub fn expand_syntax_ext<'cx>(cx: &'cx mut base::ExtCtxt,
                               sp: syntax_pos::Span,
                               tts: &[tokenstream::TokenTree])
-                              -> Box<base::MacResult + 'cx> {
+                              -> Box<dyn base::MacResult + 'cx> {
     if !cx.ecfg.enable_log_syntax() {
         feature_gate::emit_feature_err(&cx.parse_sess,
                                        "log_syntax",
diff --git a/src/libsyntax_ext/proc_macro_registrar.rs b/src/libsyntax_ext/proc_macro_registrar.rs
index ef29e5a6b02..85aa84acc42 100644
--- a/src/libsyntax_ext/proc_macro_registrar.rs
+++ b/src/libsyntax_ext/proc_macro_registrar.rs
@@ -55,7 +55,7 @@ struct CollectProcMacros<'a> {
 }
 
 pub fn modify(sess: &ParseSess,
-              resolver: &mut ::syntax::ext::base::Resolver,
+              resolver: &mut dyn (::syntax::ext::base::Resolver),
               mut krate: ast::Crate,
               is_proc_macro_crate: bool,
               is_test_crate: bool,
@@ -200,8 +200,8 @@ impl<'a> CollectProcMacros<'a> {
     }
 
     fn collect_attr_proc_macro(&mut self, item: &'a ast::Item, attr: &'a ast::Attribute) {
-        if let Some(_) = attr.meta_item_list() {
-            self.handler.span_err(attr.span, "`#[proc_macro_attribute]` attribute
+        if !attr.is_word() {
+            self.handler.span_err(attr.span, "`#[proc_macro_attribute]` attribute \
                 does not take any arguments");
             return;
         }
@@ -223,8 +223,8 @@ impl<'a> CollectProcMacros<'a> {
     }
 
     fn collect_bang_proc_macro(&mut self, item: &'a ast::Item, attr: &'a ast::Attribute) {
-        if let Some(_) = attr.meta_item_list() {
-            self.handler.span_err(attr.span, "`#[proc_macro]` attribute
+        if !attr.is_word() {
+            self.handler.span_err(attr.span, "`#[proc_macro]` attribute \
                 does not take any arguments");
             return;
         }
diff --git a/src/libsyntax_ext/trace_macros.rs b/src/libsyntax_ext/trace_macros.rs
index 48be8e0c53c..256b525b8be 100644
--- a/src/libsyntax_ext/trace_macros.rs
+++ b/src/libsyntax_ext/trace_macros.rs
@@ -18,7 +18,7 @@ use syntax::tokenstream::TokenTree;
 pub fn expand_trace_macros(cx: &mut ExtCtxt,
                            sp: Span,
                            tt: &[TokenTree])
-                           -> Box<base::MacResult + 'static> {
+                           -> Box<dyn base::MacResult + 'static> {
     if !cx.ecfg.enable_trace_macros() {
         feature_gate::emit_feature_err(&cx.parse_sess,
                                        "trace_macros",
diff --git a/src/test/ui-fulldeps/proc-macro/invalid-attributes.rs b/src/test/ui-fulldeps/proc-macro/invalid-attributes.rs
new file mode 100644
index 00000000000..c06f98ed5ff
--- /dev/null
+++ b/src/test/ui-fulldeps/proc-macro/invalid-attributes.rs
@@ -0,0 +1,36 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+#![feature(proc_macro)]
+
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+
+#[proc_macro = "test"] //~ ERROR: does not take any arguments
+pub fn a(a: TokenStream) -> TokenStream { a }
+
+#[proc_macro()] //~ ERROR: does not take any arguments
+pub fn c(a: TokenStream) -> TokenStream { a }
+
+#[proc_macro(x)] //~ ERROR: does not take any arguments
+pub fn d(a: TokenStream) -> TokenStream { a }
+
+#[proc_macro_attribute = "test"] //~ ERROR: does not take any arguments
+pub fn e(_: TokenStream, a: TokenStream) -> TokenStream { a }
+
+#[proc_macro_attribute()] //~ ERROR: does not take any arguments
+pub fn g(_: TokenStream, a: TokenStream) -> TokenStream { a }
+
+#[proc_macro_attribute(x)] //~ ERROR: does not take any arguments
+pub fn h(_: TokenStream, a: TokenStream) -> TokenStream { a }
diff --git a/src/test/ui-fulldeps/proc-macro/invalid-attributes.stderr b/src/test/ui-fulldeps/proc-macro/invalid-attributes.stderr
new file mode 100644
index 00000000000..c480bcb5df9
--- /dev/null
+++ b/src/test/ui-fulldeps/proc-macro/invalid-attributes.stderr
@@ -0,0 +1,38 @@
+error: `#[proc_macro]` attribute does not take any arguments
+  --> $DIR/invalid-attributes.rs:20:1
+   |
+LL | #[proc_macro = "test"] //~ ERROR: does not take any arguments
+   | ^^^^^^^^^^^^^^^^^^^^^^
+
+error: `#[proc_macro]` attribute does not take any arguments
+  --> $DIR/invalid-attributes.rs:23:1
+   |
+LL | #[proc_macro()] //~ ERROR: does not take any arguments
+   | ^^^^^^^^^^^^^^^
+
+error: `#[proc_macro]` attribute does not take any arguments
+  --> $DIR/invalid-attributes.rs:26:1
+   |
+LL | #[proc_macro(x)] //~ ERROR: does not take any arguments
+   | ^^^^^^^^^^^^^^^^
+
+error: `#[proc_macro_attribute]` attribute does not take any arguments
+  --> $DIR/invalid-attributes.rs:29:1
+   |
+LL | #[proc_macro_attribute = "test"] //~ ERROR: does not take any arguments
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `#[proc_macro_attribute]` attribute does not take any arguments
+  --> $DIR/invalid-attributes.rs:32:1
+   |
+LL | #[proc_macro_attribute()] //~ ERROR: does not take any arguments
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `#[proc_macro_attribute]` attribute does not take any arguments
+  --> $DIR/invalid-attributes.rs:35:1
+   |
+LL | #[proc_macro_attribute(x)] //~ ERROR: does not take any arguments
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 6 previous errors
+