Refactor how global paths are represented (for both ast and hir).

src/librustc/hir/lowering.rs

@@ -81,7 +81,7 @@ pub struct LoweringContext<'a> {
 }
 
 pub trait Resolver {
-    // Resolve a global hir path generated by the lowerer when expanding `for`, `if let`, etc.
+    // Resolve a hir path generated by the lowerer when expanding `for`, `if let`, etc.
     fn resolve_hir_path(&mut self, path: &mut hir::Path, is_value: bool);
 
     // Obtain the resolution for a node id
@@ -337,7 +337,6 @@ impl<'a> LoweringContext<'a> {
 
         let proj_start = p.segments.len() - resolution.depth;
         let path = P(hir::Path {
-            global: p.global,
             def: resolution.base_def,
             segments: p.segments[..proj_start].iter().enumerate().map(|(i, segment)| {
                 let param_mode = match (qself_position, param_mode) {
@@ -404,12 +403,17 @@ impl<'a> LoweringContext<'a> {
                         id: NodeId,
                         p: &Path,
                         name: Option<Name>,
-                        param_mode: ParamMode)
+                        param_mode: ParamMode,
+                        defaults_to_global: bool)
                         -> hir::Path {
+        let mut segments = p.segments.iter();
+        if defaults_to_global && p.is_global() {
+            segments.next();
+        }
+
         hir::Path {
-            global: p.global,
             def: self.expect_full_def(id),
-            segments: p.segments.iter().map(|segment| {
+            segments: segments.map(|segment| {
                 self.lower_path_segment(segment, param_mode)
             }).chain(name.map(|name| {
                 hir::PathSegment {
@@ -424,9 +428,10 @@ impl<'a> LoweringContext<'a> {
     fn lower_path(&mut self,
                   id: NodeId,
                   p: &Path,
-                  param_mode: ParamMode)
+                  param_mode: ParamMode,
+                  defaults_to_global: bool)
                   -> hir::Path {
-        self.lower_path_extra(id, p, None, param_mode)
+        self.lower_path_extra(id, p, None, param_mode, defaults_to_global)
     }
 
     fn lower_path_segment(&mut self,
@@ -602,8 +607,8 @@ impl<'a> LoweringContext<'a> {
                         // Check if the where clause type is a plain type parameter.
                         match bound_pred.bounded_ty.node {
                             TyKind::Path(None, ref path)
-                                    if !path.global && path.segments.len() == 1 &&
-                                        bound_pred.bound_lifetimes.is_empty() => {
+                                    if path.segments.len() == 1 &&
+                                       bound_pred.bound_lifetimes.is_empty() => {
                                 if let Some(Def::TyParam(def_id)) =
                                         self.resolver.get_resolution(bound_pred.bounded_ty.id)
                                                      .map(|d| d.base_def) {
@@ -677,7 +682,7 @@ impl<'a> LoweringContext<'a> {
                                                           span}) => {
                 hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
                     id: id,
-                    path: self.lower_path(id, path, ParamMode::Explicit),
+                    path: self.lower_path(id, path, ParamMode::Explicit, false),
                     ty: self.lower_ty(ty),
                     span: span,
                 })
@@ -707,7 +712,7 @@ impl<'a> LoweringContext<'a> {
 
     fn lower_trait_ref(&mut self, p: &TraitRef) -> hir::TraitRef {
         hir::TraitRef {
-            path: self.lower_path(p.ref_id, &p.path, ParamMode::Explicit),
+            path: self.lower_path(p.ref_id, &p.path, ParamMode::Explicit, false),
             ref_id: p.ref_id,
         }
     }
@@ -800,7 +805,7 @@ impl<'a> LoweringContext<'a> {
                             };
 
                             let mut path = self.lower_path_extra(import.id, path, suffix,
-                                                                 ParamMode::Explicit);
+                                                                 ParamMode::Explicit, true);
                             path.span = span;
                             self.items.insert(import.id, hir::Item {
                                 id: import.id,
@@ -814,7 +819,7 @@ impl<'a> LoweringContext<'a> {
                         path
                     }
                 };
-                let path = P(self.lower_path(id, path, ParamMode::Explicit));
+                let path = P(self.lower_path(id, path, ParamMode::Explicit, true));
                 let kind = match view_path.node {
                     ViewPathSimple(ident, _) => {
                         *name = ident.name;
@@ -1135,7 +1140,6 @@ impl<'a> LoweringContext<'a> {
                             Some(def) => {
                                 hir::PatKind::Path(hir::QPath::Resolved(None, P(hir::Path {
                                     span: pth1.span,
-                                    global: false,
                                     def: def,
                                     segments: hir_vec![
                                         hir::PathSegment::from_name(pth1.node.name)
@@ -1878,7 +1882,7 @@ impl<'a> LoweringContext<'a> {
             Visibility::Crate(_) => hir::Visibility::Crate,
             Visibility::Restricted { ref path, id } => {
                 hir::Visibility::Restricted {
-                    path: P(self.lower_path(id, path, ParamMode::Explicit)),
+                    path: P(self.lower_path(id, path, ParamMode::Explicit, true)),
                     id: id
                 }
             }
@@ -1971,7 +1975,6 @@ impl<'a> LoweringContext<'a> {
 
         let expr_path = hir::ExprPath(hir::QPath::Resolved(None, P(hir::Path {
             span: span,
-            global: false,
             def: def,
             segments: hir_vec![hir::PathSegment::from_name(id)],
         })));
@@ -2139,17 +2142,12 @@ impl<'a> LoweringContext<'a> {
     /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
     /// The path is also resolved according to `is_value`.
     fn std_path(&mut self, span: Span, components: &[&str], is_value: bool) -> hir::Path {
-        let idents = self.crate_root.iter().chain(components);
-
-        let segments: Vec<_> = idents.map(|name| {
-            hir::PathSegment::from_name(Symbol::intern(name))
-        }).collect();
-
         let mut path = hir::Path {
             span: span,
-            global: true,
             def: Def::Err,
-            segments: segments.into(),
+            segments: iter::once(keywords::CrateRoot.name()).chain({
+                self.crate_root.into_iter().chain(components.iter().cloned()).map(Symbol::intern)
+            }).map(hir::PathSegment::from_name).collect(),
         };
 
         self.resolver.resolve_hir_path(&mut path, is_value);

src/librustc/hir/mod.rs

@@ -105,15 +105,18 @@ pub struct LifetimeDef {
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash)]
 pub struct Path {
     pub span: Span,
-    /// A `::foo` path, is relative to the crate root rather than current
-    /// module (like paths in an import).
-    pub global: bool,
     /// The definition that the path resolved to.
     pub def: Def,
     /// The segments in the path: the things separated by `::`.
     pub segments: HirVec<PathSegment>,
 }
 
+impl Path {
+    pub fn is_global(&self) -> bool {
+        !self.segments.is_empty() && self.segments[0].name == keywords::CrateRoot.name()
+    }
+}
+
 impl fmt::Debug for Path {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "path({})", print::path_to_string(self))

src/librustc/hir/print.rs

@@ -1643,17 +1643,14 @@ impl<'a> State<'a> {
                   -> io::Result<()> {
         self.maybe_print_comment(path.span.lo)?;
 
-        let mut first = !path.global;
-        for segment in &path.segments {
-            if first {
-                first = false
-            } else {
+        for (i, segment) in path.segments.iter().enumerate() {
+            if i > 0 {
                 word(&mut self.s, "::")?
             }
-
-            self.print_name(segment.name)?;
-
-            self.print_path_parameters(&segment.parameters, colons_before_params)?;
+            if segment.name != keywords::CrateRoot.name() {
+                self.print_name(segment.name)?;
+                self.print_path_parameters(&segment.parameters, colons_before_params)?;
+            }
         }
 
         Ok(())
@@ -1673,15 +1670,14 @@ impl<'a> State<'a> {
                 space(&mut self.s)?;
                 self.word_space("as")?;
 
-                let mut first = !path.global;
-                for segment in &path.segments[..path.segments.len() - 1] {
-                    if first {
-                        first = false
-                    } else {
+                for (i, segment) in path.segments[..path.segments.len() - 1].iter().enumerate() {
+                    if i > 0 {
                         word(&mut self.s, "::")?
                     }
-                    self.print_name(segment.name)?;
-                    self.print_path_parameters(&segment.parameters, colons_before_params)?;
+                    if segment.name != keywords::CrateRoot.name() {
+                        self.print_name(segment.name)?;
+                        self.print_path_parameters(&segment.parameters, colons_before_params)?;
+                    }
                 }
 
                 word(&mut self.s, ">")?;

src/librustc/infer/error_reporting.rs

@@ -1620,7 +1620,6 @@ impl<'a, 'gcx, 'tcx> Rebuilder<'a, 'gcx, 'tcx> {
         new_segs.push(new_seg);
         hir::Path {
             span: path.span,
-            global: path.global,
             def: path.def,
             segments: new_segs.into()
         }

src/librustc_const_eval/_match.rs

@@ -324,7 +324,6 @@ impl Witness {
                     let v = ctor.variant_for_adt(adt);
                     let qpath = hir::QPath::Resolved(None, P(hir::Path {
                         span: DUMMY_SP,
-                        global: false,
                         def: Def::Err,
                         segments: vec![hir::PathSegment::from_name(v.name)].into(),
                     }));

src/librustc_incremental/calculate_svh/svh_visitor.rs

@@ -189,7 +189,6 @@ enum SawAbiComponent<'a> {
     SawStructField,
     SawVariant,
     SawQPath,
-    SawPath(bool),
     SawPathSegment,
     SawPathParameters,
     SawBlock,
@@ -678,7 +677,6 @@ impl<'a, 'hash, 'tcx> visit::Visitor<'tcx> for StrictVersionHashVisitor<'a, 'has
 
     fn visit_path(&mut self, path: &'tcx Path, _: ast::NodeId) {
         debug!("visit_path: st={:?}", self.st);
-        SawPath(path.global).hash(self.st);
         hash_span!(self, path.span);
         visit::walk_path(self, path)
     }

src/librustc_lint/bad_style.rs

@@ -382,7 +382,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NonUpperCaseGlobals {
     fn check_pat(&mut self, cx: &LateContext, p: &hir::Pat) {
         // Lint for constants that look like binding identifiers (#7526)
         if let PatKind::Path(hir::QPath::Resolved(None, ref path)) = p.node {
-            if !path.global && path.segments.len() == 1 && path.segments[0].parameters.is_empty() {
+            if path.segments.len() == 1 && path.segments[0].parameters.is_empty() {
                 if let Def::Const(..) = path.def {
                     NonUpperCaseGlobals::check_upper_case(cx,
                                                           "constant in pattern",

src/librustc_passes/ast_validation.rs

@@ -154,8 +154,8 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
     }
 
     fn visit_path(&mut self, path: &'a Path, id: NodeId) {
-        if path.global && path.segments.len() > 0 {
-            let ident = path.segments[0].identifier;
+        if path.segments.len() >= 2 && path.is_global() {
+            let ident = path.segments[1].identifier;
             if token::Ident(ident).is_path_segment_keyword() {
                 self.session.add_lint(lint::builtin::SUPER_OR_SELF_IN_GLOBAL_PATH,
                                       id,

src/librustc_resolve/build_reduced_graph.rs

@@ -40,6 +40,7 @@ use syntax::ext::base::Determinacy::Undetermined;
 use syntax::ext::expand::mark_tts;
 use syntax::ext::hygiene::Mark;
 use syntax::ext::tt::macro_rules;
+use syntax::parse::token;
 use syntax::symbol::keywords;
 use syntax::visit::{self, Visitor};
 
@@ -112,7 +113,7 @@ impl<'a> Resolver<'a> {
                 // Extract and intern the module part of the path. For
                 // globs and lists, the path is found directly in the AST;
                 // for simple paths we have to munge the path a little.
-                let module_path: Vec<_> = match view_path.node {
+                let mut module_path: Vec<_> = match view_path.node {
                     ViewPathSimple(_, ref full_path) => {
                         full_path.segments
                                  .split_last()
@@ -132,6 +133,12 @@ impl<'a> Resolver<'a> {
                     }
                 };
 
+                // This can be removed once warning cycle #36888 is complete.
+                if module_path.len() >= 2 && module_path[0].name == keywords::CrateRoot.name() &&
+                   token::Ident(module_path[1]).is_path_segment_keyword() {
+                    module_path.remove(0);
+                }
+
                 // Build up the import directives.
                 let is_prelude = attr::contains_name(&item.attrs, "prelude_import");
 
@@ -193,18 +200,16 @@ impl<'a> Resolver<'a> {
                                     let rename = node.rename.unwrap_or(node.name);
                                     (module_path.clone(), node.name, rename)
                                 } else {
-                                    let ident = match module_path.last() {
-                                        Some(&ident) => ident,
-                                        None => {
-                                            resolve_error(
-                                                self,
-                                                source_item.span,
-                                                ResolutionError::
-                                                SelfImportOnlyInImportListWithNonEmptyPrefix
-                                            );
-                                            continue;
-                                        }
-                                    };
+                                    let ident = *module_path.last().unwrap();
+                                    if ident.name == keywords::CrateRoot.name() {
+                                        resolve_error(
+                                            self,
+                                            source_item.span,
+                                            ResolutionError::
+                                            SelfImportOnlyInImportListWithNonEmptyPrefix
+                                        );
+                                        continue;
+                                    }
                                     let module_path = module_path.split_last().unwrap().1;
                                     let rename = node.rename.unwrap_or(ident);
                                     (module_path.to_vec(), ident, rename)