Auto merge of #56042 - petrochenkov:nuni, r=petrochenkov

[nightly] resolve: Implement uniform paths 2.0

Forward-port of #55884 to nightly.

r? @ghost

src/doc/unstable-book/src/language-features/extern-in-paths.md

@@ -11,8 +11,8 @@ introducing `extern crate` items, using keyword `extern`.
 
 For example, `extern::my_crat::a::b` will resolve to path `a::b` in crate `my_crate`.
 
-`feature(extern_absolute_paths)` mode provides the same effect by resolving absolute paths like
-`::my_crate::a::b` to paths from extern crates by default.
+Absolute paths on 2018 edition (e.g. `::my_crate::a::b`) provide the same effect
+and resolve to extern crates (built-in or passed with `--extern`).
 
 ```rust,ignore
 #![feature(extern_in_paths)]

src/librustc/hir/def.rs

@@ -128,14 +128,6 @@ impl PathResolution {
     pub fn unresolved_segments(&self) -> usize {
         self.unresolved_segments
     }
-
-    pub fn kind_name(&self) -> &'static str {
-        if self.unresolved_segments != 0 {
-            "associated item"
-        } else {
-            self.base_def.kind_name()
-        }
-    }
 }
 
 /// Different kinds of symbols don't influence each other.
@@ -269,27 +261,33 @@ impl NonMacroAttrKind {
 
 impl Def {
     pub fn def_id(&self) -> DefId {
+        self.opt_def_id().unwrap_or_else(|| {
+            bug!("attempted .def_id() on invalid def: {:?}", self)
+        })
+    }
+
+    pub fn opt_def_id(&self) -> Option<DefId> {
         match *self {
             Def::Fn(id) | Def::Mod(id) | Def::Static(id, _) |
             Def::Variant(id) | Def::VariantCtor(id, ..) | Def::Enum(id) |
             Def::TyAlias(id) | Def::TraitAlias(id) |
             Def::AssociatedTy(id) | Def::TyParam(id) | Def::Struct(id) | Def::StructCtor(id, ..) |
             Def::Union(id) | Def::Trait(id) | Def::Method(id) | Def::Const(id) |
             Def::AssociatedConst(id) | Def::Macro(id, ..) |
-            Def::Existential(id) | Def::AssociatedExistential(id) | Def::ForeignTy(id) |
-            Def::SelfCtor(id) => {
-                id
+            Def::Existential(id) | Def::AssociatedExistential(id) | Def::ForeignTy(id) => {
+                Some(id)
             }
 
             Def::Local(..) |
             Def::Upvar(..) |
             Def::Label(..)  |
             Def::PrimTy(..) |
             Def::SelfTy(..) |
+            Def::SelfCtor(..) |
             Def::ToolMod |
             Def::NonMacroAttr(..) |
             Def::Err => {
-                bug!("attempted .def_id() on invalid def: {:?}", self)
+                None
             }
         }
     }
@@ -333,4 +331,13 @@ impl Def {
             Def::Err => "unresolved item",
         }
     }
+
+    pub fn article(&self) -> &'static str {
+        match *self {
+            Def::AssociatedTy(..) | Def::AssociatedConst(..) | Def::AssociatedExistential(..) |
+            Def::Enum(..) | Def::Existential(..) | Def::Err => "an",
+            Def::Macro(.., macro_kind) => macro_kind.article(),
+            _ => "a",
+        }
+    }
 }

src/librustc/hir/def_id.rs

@@ -225,8 +225,8 @@ pub struct DefId {
 
 impl fmt::Debug for DefId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "DefId({:?}/{}:{}",
-               self.krate.index(),
+        write!(f, "DefId({}/{}:{}",
+               self.krate,
                self.index.address_space().index(),
                self.index.as_array_index())?;
 

src/librustc/middle/dead.rs

@@ -80,7 +80,7 @@ impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
                 self.check_def_id(def.def_id());
             }
             _ if self.in_pat => (),
-            Def::PrimTy(..) | Def::SelfTy(..) |
+            Def::PrimTy(..) | Def::SelfTy(..) | Def::SelfCtor(..) |
             Def::Local(..) | Def::Upvar(..) => {}
             Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
                 if let Some(enum_id) = self.tcx.parent_def_id(variant_id) {

src/librustc/middle/stability.rs

@@ -781,10 +781,8 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
 
     fn visit_path(&mut self, path: &'tcx hir::Path, id: hir::HirId) {
         let id = self.tcx.hir.hir_to_node_id(id);
-        match path.def {
-            Def::Local(..) | Def::Upvar(..) | Def::SelfCtor(..) |
-            Def::PrimTy(..) | Def::SelfTy(..) | Def::Err => {}
-            _ => self.tcx.check_stability(path.def.def_id(), Some(id), path.span)
+        if let Some(def_id) = path.def.opt_def_id() {
+            self.tcx.check_stability(def_id, Some(id), path.span)
         }
         intravisit::walk_path(self, path)
     }

src/librustc_mir/hair/pattern/check_match.rs

@@ -298,7 +298,8 @@ impl<'a, 'tcx> MatchVisitor<'a, 'tcx> {
             let label_msg = match pat.node {
                 PatKind::Path(hir::QPath::Resolved(None, ref path))
                         if path.segments.len() == 1 && path.segments[0].args.is_none() => {
-                    format!("interpreted as a {} pattern, not new variable", path.def.kind_name())
+                    format!("interpreted as {} {} pattern, not new variable",
+                            path.def.article(), path.def.kind_name())
                 }
                 _ => format!("pattern `{}` not covered", pattern_string),
             };

src/librustc_privacy/lib.rs

@@ -361,9 +361,11 @@ impl<'a, 'tcx> Visitor<'tcx> for EmbargoVisitor<'a, 'tcx> {
             let def_id = self.tcx.hir.local_def_id(id);
             if let Some(exports) = self.tcx.module_exports(def_id) {
                 for export in exports.iter() {
-                    if let Some(node_id) = self.tcx.hir.as_local_node_id(export.def.def_id()) {
-                        if export.vis == ty::Visibility::Public {
-                            self.update(node_id, Some(AccessLevel::Exported));
+                    if export.vis == ty::Visibility::Public {
+                        if let Some(def_id) = export.def.opt_def_id() {
+                            if let Some(node_id) = self.tcx.hir.as_local_node_id(def_id) {
+                                self.update(node_id, Some(AccessLevel::Exported));
+                            }
                         }
                     }
                 }