Improve pretty printing `$crate::` paths.

src/librustc/hir/lowering.rs

@@ -175,7 +175,7 @@ pub fn lower_crate(sess: &Session,
     let _ignore = dep_graph.in_ignore();
 
     LoweringContext {
-        crate_root: std_inject::injected_crate_name(krate),
+        crate_root: std_inject::injected_crate_name(),
         sess,
         cstore,
         parent_def: None,

src/librustc_resolve/build_reduced_graph.rs

@@ -40,6 +40,7 @@ use syntax::ext::base::Determinacy::Undetermined;
 use syntax::ext::hygiene::Mark;
 use syntax::ext::tt::macro_rules;
 use syntax::parse::token::{self, Token};
+use syntax::std_inject::injected_crate_name;
 use syntax::symbol::keywords;
 use syntax::symbol::Symbol;
 use syntax::visit::{self, Visitor};
@@ -262,7 +263,7 @@ impl<'a> Resolver<'a> {
                 let module =
                     self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
                 self.populate_module_if_necessary(module);
-                if self.injected_crate_name.map_or(false, |name| item.ident.name == name) {
+                if injected_crate_name().map_or(false, |name| item.ident.name == name) {
                     self.injected_crate = Some(module);
                 }
 

src/librustc_resolve/lib.rs

@@ -58,7 +58,6 @@ use syntax::ast::{Item, ItemKind, ImplItem, ImplItemKind};
 use syntax::ast::{Local, Mutability, Pat, PatKind, Path};
 use syntax::ast::{QSelf, TraitItemKind, TraitRef, Ty, TyKind};
 use syntax::feature_gate::{feature_err, emit_feature_err, GateIssue};
-use syntax::std_inject::injected_crate_name;
 
 use syntax_pos::{Span, DUMMY_SP, MultiSpan};
 use errors::{DiagnosticBuilder, DiagnosticId};
@@ -1335,7 +1334,6 @@ pub struct Resolver<'a> {
     // Only used for better errors on `fn(): fn()`
     current_type_ascription: Vec<Span>,
 
-    injected_crate_name: Option<&'static str>,
     injected_crate: Option<Module<'a>>,
 }
 
@@ -1536,7 +1534,6 @@ impl<'a> Resolver<'a> {
             found_unresolved_macro: false,
             unused_macros: FxHashSet(),
             current_type_ascription: Vec::new(),
-            injected_crate_name: injected_crate_name(krate),
             injected_crate: None,
         }
     }

src/librustc_resolve/macros.rs

@@ -25,7 +25,7 @@ use syntax::errors::DiagnosticBuilder;
 use syntax::ext::base::{self, Annotatable, Determinacy, MultiModifier, MultiDecorator};
 use syntax::ext::base::{MacroKind, SyntaxExtension, Resolver as SyntaxResolver};
 use syntax::ext::expand::{Expansion, ExpansionKind, Invocation, InvocationKind, find_attr_invoc};
-use syntax::ext::hygiene::Mark;
+use syntax::ext::hygiene::{Mark, MarkKind};
 use syntax::ext::placeholders::placeholder;
 use syntax::ext::tt::macro_rules;
 use syntax::feature_gate::{self, emit_feature_err, GateIssue};
@@ -297,16 +297,19 @@ impl<'a> base::Resolver for Resolver<'a> {
             InvocationKind::Attr { attr: None, .. } => return Ok(None),
             _ => self.resolve_invoc_to_def(invoc, scope, force)?,
         };
+        let def_id = def.def_id();
 
-        self.macro_defs.insert(invoc.expansion_data.mark, def.def_id());
+        self.macro_defs.insert(invoc.expansion_data.mark, def_id);
         let normal_module_def_id =
             self.macro_def_scope(invoc.expansion_data.mark).normal_ancestor_id;
         self.definitions.add_macro_def_scope(invoc.expansion_data.mark, normal_module_def_id);
 
-        self.unused_macros.remove(&def.def_id());
+        self.unused_macros.remove(&def_id);
         let ext = self.get_macro(def);
         if ext.is_modern() {
-            invoc.expansion_data.mark.set_modern();
+            invoc.expansion_data.mark.set_kind(MarkKind::Modern);
+        } else if def_id.krate == BUILTIN_MACROS_CRATE {
+            invoc.expansion_data.mark.set_kind(MarkKind::Builtin);
         }
         Ok(Some(ext))
     }

src/libsyntax/print/pprust.rs

@@ -18,6 +18,7 @@ use util::parser::{self, AssocOp, Fixity};
 use attr;
 use codemap::{self, CodeMap};
 use syntax_pos::{self, BytePos};
+use syntax_pos::hygiene::{Mark, MarkKind, SyntaxContext};
 use parse::token::{self, BinOpToken, Token};
 use parse::lexer::comments;
 use parse::{self, ParseSess};
@@ -93,7 +94,7 @@ pub fn print_crate<'a>(cm: &'a CodeMap,
                        is_expanded: bool) -> io::Result<()> {
     let mut s = State::new_from_input(cm, sess, filename, input, out, ann, is_expanded);
 
-    if is_expanded && !std_inject::injected_crate_name(krate).is_none() {
+    if is_expanded && !std_inject::injected_crate_name().is_none() {
         // We need to print `#![no_std]` (and its feature gate) so that
         // compiling pretty-printed source won't inject libstd again.
         // However we don't want these attributes in the AST because
@@ -734,6 +735,8 @@ pub trait PrintState<'a> {
                     if segment.identifier.name != keywords::CrateRoot.name() &&
                        segment.identifier.name != keywords::DollarCrate.name() {
                         self.writer().word(&segment.identifier.name.as_str())?;
+                    } else if segment.identifier.name == keywords::DollarCrate.name() {
+                        self.print_dollar_crate(segment.identifier.ctxt)?;
                     }
                 }
                 self.writer().space()?;
@@ -822,6 +825,19 @@ pub trait PrintState<'a> {
     }
 
     fn nbsp(&mut self) -> io::Result<()> { self.writer().word(" ") }
+
+    fn print_dollar_crate(&mut self, mut ctxt: SyntaxContext) -> io::Result<()> {
+        if let Some(mark) = ctxt.adjust(Mark::root()) {
+            // Make a best effort to print something that complies
+            if mark.kind() == MarkKind::Builtin {
+                if let Some(name) = std_inject::injected_crate_name() {
+                    self.writer().word("::")?;
+                    self.writer().word(name)?;
+                }
+            }
+        }
+        Ok(())
+    }
 }
 
 impl<'a> PrintState<'a> for State<'a> {
@@ -2411,6 +2427,8 @@ impl<'a> State<'a> {
             if let Some(ref parameters) = segment.parameters {
                 self.print_path_parameters(parameters, colons_before_params)?;
             }
+        } else if segment.identifier.name == keywords::DollarCrate.name() {
+            self.print_dollar_crate(segment.identifier.ctxt)?;
         }
         Ok(())
     }

src/libsyntax/std_inject.rs

@@ -10,6 +10,7 @@
 
 use ast;
 use attr;
+use std::cell::Cell;
 use ext::hygiene::{Mark, SyntaxContext};
 use symbol::{Symbol, keywords};
 use syntax_pos::{DUMMY_SP, Span};
@@ -34,22 +35,25 @@ fn ignored_span(sp: Span) -> Span {
     sp.with_ctxt(SyntaxContext::empty().apply_mark(mark))
 }
 
-pub fn injected_crate_name(krate: &ast::Crate) -> Option<&'static str> {
-    if attr::contains_name(&krate.attrs, "no_core") {
-        None
-    } else if attr::contains_name(&krate.attrs, "no_std") {
-        Some("core")
-    } else {
-        Some("std")
-    }
+pub fn injected_crate_name() -> Option<&'static str> {
+    INJECTED_CRATE_NAME.with(|name| name.get())
+}
+
+thread_local! {
+    static INJECTED_CRATE_NAME: Cell<Option<&'static str>> = Cell::new(None);
 }
 
 pub fn maybe_inject_crates_ref(mut krate: ast::Crate, alt_std_name: Option<String>) -> ast::Crate {
-    let name = match injected_crate_name(&krate) {
-        Some(name) => name,
-        None => return krate,
+    let name = if attr::contains_name(&krate.attrs, "no_core") {
+        return krate;
+    } else if attr::contains_name(&krate.attrs, "no_std") {
+        "core"
+    } else {
+        "std"
     };
 
+    INJECTED_CRATE_NAME.with(|opt_name| opt_name.set(Some(name)));
+
     let crate_name = Symbol::intern(&alt_std_name.unwrap_or_else(|| name.to_string()));
 
     krate.module.items.insert(0, P(ast::Item {