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

Unaccept `extern_in_paths`

Based on completed fcp-close in #55600, this removes `extern_in_path` (e.g. `extern::foo::bar`) from the language. The changes are primarily reversing 32db83b.

Closes #55600

r? @petrochenkov

Author: Centril

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

@@ -140,7 +140,7 @@ pub enum ExternCrateSource {
     ),
     // Crate is loaded by `use`.
     Use,
-    /// Crate is implicitly loaded by an absolute or an `extern::` path.
+    /// Crate is implicitly loaded by an absolute path.
     Path,
 }
 

src/librustc/middle/cstore.rs

@@ -1015,7 +1015,7 @@ enum ModuleOrUniformRoot<'a> {
     CrateRootAndExternPrelude,
 
     /// Virtual module that denotes resolution in extern prelude.
-    /// Used for paths starting with `::` on 2018 edition or `extern::`.
+    /// Used for paths starting with `::` on 2018 edition.
     ExternPrelude,
 
     /// Virtual module that denotes resolution in current scope.
@@ -3836,8 +3836,7 @@ impl<'a> Resolver<'a> {
                             self.resolve_self(&mut ctxt, self.current_module)));
                         continue;
                     }
-                    if name == keywords::Extern.name() ||
-                       name == keywords::PathRoot.name() && ident.span.rust_2018() {
+                    if name == keywords::PathRoot.name() && ident.span.rust_2018() {
                         module = Some(ModuleOrUniformRoot::ExternPrelude);
                         continue;
                     }
@@ -4004,8 +4003,8 @@ impl<'a> Resolver<'a> {
         };
 
         // We're only interested in `use` paths which should start with
-        // `{{root}}` or `extern` currently.
-        if first_name != keywords::Extern.name() && first_name != keywords::PathRoot.name() {
+        // `{{root}}` currently.
+        if first_name != keywords::PathRoot.name() {
             return
         }
 

src/librustc_resolve/lib.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,

src/libsyntax/feature_gate.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)?;

src/libsyntax/parse/parser.rs

@@ -478,7 +478,6 @@ impl Ident {
         self.name == keywords::Super.name() ||
         self.name == keywords::SelfLower.name() ||
         self.name == keywords::SelfUpper.name() ||
-        self.name == keywords::Extern.name() ||
         self.name == keywords::Crate.name() ||
         self.name == keywords::PathRoot.name() ||
         self.name == keywords::DollarCrate.name()

src/libsyntax_pos/symbol.rs

@@ -1,12 +1,9 @@
 -include ../tools.mk
 
-all: extern_absolute_paths.rs extern_in_paths.rs krate2
+all: extern_absolute_paths.rs krate2
 	$(RUSTC) extern_absolute_paths.rs -Zsave-analysis --edition=2018 \
 		-Z unstable-options --extern krate2
 	cat $(TMPDIR)/save-analysis/extern_absolute_paths.json | "$(PYTHON)" validate_json.py
-	$(RUSTC) extern_in_paths.rs -Zsave-analysis --edition=2018 \
-		-Z unstable-options --extern krate2
-	cat $(TMPDIR)/save-analysis/extern_in_paths.json | "$(PYTHON)" validate_json.py
 
 krate2: krate2.rs
 	$(RUSTC) $<

src/test/run-make-fulldeps/save-analysis-rfc2126/Makefile

@@ -0,0 +1,3 @@
+fn main() {
+    let s = extern::foo::Bar; //~ ERROR expected expression, found keyword `extern`
+}

src/test/run-make-fulldeps/save-analysis-rfc2126/extern_in_paths.rs

@@ -0,0 +1,8 @@
+error: expected expression, found keyword `extern`
+  --> $DIR/keyword-extern-as-identifier-expr.rs:2:13
+   |
+LL |     let s = extern::foo::Bar; //~ ERROR expected expression, found keyword `extern`
+   |             ^^^^^^ expected expression
+
+error: aborting due to previous error
+

src/test/run-pass/rfcs/rfc-2126-extern-absolute-paths/extern.rs

@@ -0,0 +1,3 @@
+fn main() {
+    let extern = 0; //~ ERROR expected pattern, found keyword `extern`
+}

src/test/ui/feature-gates/feature-gate-extern_in_paths.rs

@@ -0,0 +1,8 @@
+error: expected pattern, found keyword `extern`
+  --> $DIR/keyword-extern-as-identifier-pat.rs:2:9
+   |
+LL |     let extern = 0; //~ ERROR expected pattern, found keyword `extern`
+   |         ^^^^^^ expected pattern
+
+error: aborting due to previous error
+

src/test/ui/feature-gates/feature-gate-extern_in_paths.stderr

@@ -0,0 +1,3 @@
+type A = extern::foo::bar; //~ ERROR expected `fn`, found `::`
+
+fn main() {}

src/test/ui/keyword/extern/keyword-extern-as-identifier-expr.rs

@@ -0,0 +1,8 @@
+error: expected `fn`, found `::`
+  --> $DIR/keyword-extern-as-identifier-type.rs:1:16
+   |
+LL | type A = extern::foo::bar; //~ ERROR expected `fn`, found `::`
+   |                ^^ expected `fn` here
+
+error: aborting due to previous error
+

src/test/ui/keyword/extern/keyword-extern-as-identifier-expr.stderr

@@ -0,0 +1,3 @@
+use extern::foo; //~ ERROR expected identifier, found keyword `extern`
+
+fn main() {}

src/test/ui/keyword/extern/keyword-extern-as-identifier-pat.rs

@@ -0,0 +1,12 @@
+error: expected identifier, found keyword `extern`
+  --> $DIR/keyword-extern-as-identifier-use.rs:1:5
+   |
+LL | use extern::foo; //~ ERROR expected identifier, found keyword `extern`
+   |     ^^^^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL | use r#extern::foo; //~ ERROR expected identifier, found keyword `extern`
+   |     ^^^^^^^^
+
+error: aborting due to previous error
+