Rollup merge of #57572 - Centril:unaccept-extern-in-path, r=petrochenkov

Unaccept `extern_in_paths`

Based on completed fcp-close in https://github.com/rust-lang/rust/issues/55600, this removes `extern_in_path` (e.g. `extern::foo::bar`) from the language. The changes are primarily reversing https://github.com/rust-lang/rust/commit/32db83b16e06cb5cca72d0e6a648a8008eda0fac.

Closes https://github.com/rust-lang/rust/issues/55600

r? @petrochenkov

2 files changed, 8 insertions, 34 deletions

diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index ac20a62f117..ed278e834cb 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -25,9 +25,9 @@ use syntax_pos::{Span, DUMMY_SP};
 use errors::{DiagnosticBuilder, Handler};
 use visit::{self, FnKind, Visitor};
 use parse::ParseSess;
-use symbol::{keywords, Symbol};
+use symbol::Symbol;
 
-use std::{env};
+use std::env;
 
 macro_rules! set {
     ($field: ident) => {{
@@ -372,9 +372,6 @@ declare_features! (
     // Generic associated types (RFC 1598)
     (active, generic_associated_types, "1.23.0", Some(44265), None),
 
-    // `extern` in paths
-    (active, extern_in_paths, "1.23.0", Some(55600), None),
-
     // Infer static outlives requirements (RFC 2093).
     (active, infer_static_outlives_requirements, "1.26.0", Some(54185), None),
 
@@ -503,6 +500,9 @@ declare_features! (
     // Allows the use of `#[derive(Anything)]` as sugar for `#[derive_Anything]`.
     (removed, custom_derive, "1.0.0", Some(29644), None,
      Some("subsumed by `#[proc_macro_derive]`")),
+    // Paths of the form: `extern::foo::bar`
+    (removed, extern_in_paths, "1.33.0", Some(55600), None,
+     Some("subsumed by `::foo::bar` paths")),
 );
 
 declare_features! (
@@ -1827,25 +1827,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         visit::walk_impl_item(self, ii);
     }
 
-    fn visit_path(&mut self, path: &'a ast::Path, _id: NodeId) {
-        for segment in &path.segments {
-            // Identifiers we are going to check could come from a legacy macro (e.g., `#[test]`).
-            // For such macros identifiers must have empty context, because this context is
-            // used during name resolution and produced names must be unhygienic for compatibility.
-            // On the other hand, we need the actual non-empty context for feature gate checking
-            // because it's hygienic even for legacy macros. As previously stated, such context
-            // cannot be kept in identifiers, so it's kept in paths instead and we take it from
-            // there while keeping location info from the ident span.
-            let span = segment.ident.span.with_ctxt(path.span.ctxt());
-            if segment.ident.name == keywords::Extern.name() {
-                gate_feature_post!(&self, extern_in_paths, span,
-                                   "`extern` in paths is experimental");
-            }
-        }
-
-        visit::walk_path(self, path);
-    }
-
     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
         if let ast::VisibilityKind::Crate(ast::CrateSugar::JustCrate) = vis.node {
             gate_feature_post!(&self, crate_visibility_modifier, vis.span,
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 06ba3bbd402..119bd6c107c 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -1302,7 +1302,7 @@ impl<'a> Parser<'a> {
     fn token_is_bare_fn_keyword(&mut self) -> bool {
         self.check_keyword(keywords::Fn) ||
             self.check_keyword(keywords::Unsafe) ||
-            self.check_keyword(keywords::Extern) && self.is_extern_non_path()
+            self.check_keyword(keywords::Extern)
     }
 
     /// parse a `TyKind::BareFn` type:
@@ -4617,10 +4617,6 @@ impl<'a> Parser<'a> {
         self.token.is_keyword(keywords::Crate) && self.look_ahead(1, |t| t != &token::ModSep)
     }
 
-    fn is_extern_non_path(&self) -> bool {
-        self.token.is_keyword(keywords::Extern) && self.look_ahead(1, |t| t != &token::ModSep)
-    }
-
     fn is_existential_type_decl(&self) -> bool {
         self.token.is_keyword(keywords::Existential) &&
         self.look_ahead(1, |t| t.is_keyword(keywords::Type))
@@ -4724,12 +4720,10 @@ impl<'a> Parser<'a> {
         // like a path (1 token), but it fact not a path.
         // `union::b::c` - path, `union U { ... }` - not a path.
         // `crate::b::c` - path, `crate struct S;` - not a path.
-        // `extern::b::c` - path, `extern crate c;` - not a path.
         } else if self.token.is_path_start() &&
                   !self.token.is_qpath_start() &&
                   !self.is_union_item() &&
                   !self.is_crate_vis() &&
-                  !self.is_extern_non_path() &&
                   !self.is_existential_type_decl() &&
                   !self.is_auto_trait_item() {
             let pth = self.parse_path(PathStyle::Expr)?;
@@ -7198,8 +7192,7 @@ impl<'a> Parser<'a> {
             return Ok(Some(item));
         }
 
-        if self.check_keyword(keywords::Extern) && self.is_extern_non_path() {
-            self.bump(); // `extern`
+        if self.eat_keyword(keywords::Extern) {
             if self.eat_keyword(keywords::Crate) {
                 return Ok(Some(self.parse_item_extern_crate(lo, visibility, attrs)?));
             }
@@ -7708,7 +7701,7 @@ impl<'a> Parser<'a> {
     fn parse_assoc_macro_invoc(&mut self, item_kind: &str, vis: Option<&Visibility>,
                                at_end: &mut bool) -> PResult<'a, Option<Mac>>
     {
-        if self.token.is_path_start() && !self.is_extern_non_path() {
+        if self.token.is_path_start() {
             let prev_span = self.prev_span;
             let lo = self.span;
             let pth = self.parse_path(PathStyle::Mod)?;