Support extern in paths

Author: petrochenkov

src/librustc_resolve/lib.rs

@@ -2982,6 +2982,8 @@ impl<'a> Resolver<'a> {
  let msg = "There are too many initial `super`s.".to_string();
  return PathResult::Failed(ident.span, msg, false);
  }
+ } else if i == 0 && ns == TypeNS && name == keywords::Extern.name() {
+ continue;
  }
  allow_super = false;
 
@@ -2996,16 +2998,19 @@ impl<'a> Resolver<'a> {
  // `$crate::a::b`
  module = Some(self.resolve_crate_root(ident.node.ctxt));
  continue
- } else if i == 1 && self.session.features.borrow().extern_absolute_paths &&
- path[0].node.name == keywords::CrateRoot.name() &&
- !token::Ident(ident.node).is_path_segment_keyword() {
- // `::extern_crate::a::b`
- let crate_id = self.crate_loader.resolve_crate_from_path(name, ident.span);
- let crate_root =
- self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
- self.populate_module_if_necessary(crate_root);
- module = Some(crate_root);
- continue
+ } else if i == 1 && !token::Ident(ident.node).is_path_segment_keyword() {
+ let prev_name = path[0].node.name;
+ if prev_name == keywords::Extern.name() ||
+ prev_name == keywords::CrateRoot.name() &&
+ self.session.features.borrow().extern_absolute_paths {
+ // `::extern_crate::a::b`
+ let crate_id = self.crate_loader.resolve_crate_from_path(name, ident.span);
+ let crate_root =
+ self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
+ self.populate_module_if_necessary(crate_root);
+ module = Some(crate_root);
+ continue
+ }
  }
  }
 
@@ -3015,6 +3020,7 @@ impl<'a> Resolver<'a> {
  name == keywords::SelfValue.name() && i != 0 ||
  name == keywords::SelfType.name() && i != 0 ||
  name == keywords::Super.name() && i != 0 ||
+ name == keywords::Extern.name() && i != 0 ||
  name == keywords::Crate.name() && i != 1 &&
  path[0].node.name != keywords::CrateRoot.name() {
  let name_str = if name == keywords::CrateRoot.name() {

src/librustc_resolve/resolve_imports.rs

@@ -604,26 +604,28 @@ impl<'a, 'b:'a> ImportResolver<'a, 'b> {
  self.current_module = directive.parent;
  let ImportDirective { ref module_path, span, .. } = *directive;
 
- // Extern crate mode for absolute paths needs some
- // special support for single-segment imports.
- let extern_absolute_paths = self.session.features.borrow().extern_absolute_paths;
- if module_path.len() == 1 && module_path[0].node.name == keywords::CrateRoot.name() {
+ // FIXME: Last path segment is treated specially in import resolution, so extern crate
+ // mode for absolute paths needs some special support for single-segment imports.
+ if module_path.len() == 1 && (module_path[0].node.name == keywords::CrateRoot.name() ||
+ module_path[0].node.name == keywords::Extern.name()) {
+ let is_extern = module_path[0].node.name == keywords::Extern.name() ||
+ self.session.features.borrow().extern_absolute_paths;
  match directive.subclass {
- GlobImport { .. } if extern_absolute_paths => {
+ GlobImport { .. } if is_extern => {
  return Some((directive.span,
  "cannot glob-import all possible crates".to_string()));
  }
  SingleImport { source, target, .. } => {
- let crate_root = if source.name == keywords::Crate.name() {
+ let crate_root = if source.name == keywords::Crate.name() &&
+ module_path[0].node.name != keywords::Extern.name() {
  if target.name == keywords::Crate.name() {
  return Some((directive.span,
  "crate root imports need to be explicitly named: \
  `use crate as name;`".to_string()));
  } else {
  Some(self.resolve_crate_root(source.ctxt.modern()))
  }
- } else if extern_absolute_paths &&
- !token::Ident(source).is_path_segment_keyword() {
+ } else if is_extern && !token::Ident(source).is_path_segment_keyword() {
  let crate_id =
  self.crate_loader.resolve_crate_from_path(source.name, directive.span);
  let crate_root =

src/libsyntax/feature_gate.rs

@@ -450,6 +450,9 @@ declare_features! (
 
  // Allows use of the :lifetime macro fragment specifier
  (active, macro_lifetime_matcher, "1.24.0", Some(46895)),
+
+ // `extern` in paths
+ (active, extern_in_paths, "1.23.0", Some(44660)),
 );
 
 declare_features! (
@@ -1790,6 +1793,9 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
  if segment.identifier.name == keywords::Crate.name() {
  gate_feature_post!(&self, crate_in_paths, segment.span,
  "`crate` in paths is experimental");
+ } else if segment.identifier.name == keywords::Extern.name() {
+ gate_feature_post!(&self, extern_in_paths, segment.span,
+ "`extern` in paths is experimental");
  }
  }
 

src/libsyntax/parse/parser.rs

@@ -1387,7 +1387,7 @@ impl<'a> Parser<'a> {
  None
  };
  (ident, TraitItemKind::Const(ty, default), ast::Generics::default())
- } else if self.token.is_path_start() {
+ } else if self.token.is_path_start() && !self.is_extern_non_path() {
  // trait item macro.
  // code copied from parse_macro_use_or_failure... abstraction!
  let prev_span = self.prev_span;
@@ -4037,6 +4037,10 @@ 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 eat_auto_trait(&mut self) -> bool {
  if self.token.is_keyword(keywords::Auto)
  && self.look_ahead(1, |t| t.is_keyword(keywords::Trait))
@@ -4152,10 +4156,12 @@ 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_crate_vis() &&
+ !self.is_extern_non_path() {
  let pth = self.parse_path(PathStyle::Expr)?;
 
  if !self.eat(&token::Not) {
@@ -5236,7 +5242,7 @@ impl<'a> Parser<'a> {
  -> PResult<'a, (Ident, Vec<ast::Attribute>, ast::Generics,
  ast::ImplItemKind)> {
  // code copied from parse_macro_use_or_failure... abstraction!
- if self.token.is_path_start() {
+ if self.token.is_path_start() && !self.is_extern_non_path() {
  // Method macro.
 
  let prev_span = self.prev_span;
@@ -6238,7 +6244,8 @@ impl<'a> Parser<'a> {
  return Ok(Some(item));
  }
 
- if self.eat_keyword(keywords::Extern) {
+ if self.check_keyword(keywords::Extern) && self.is_extern_non_path() {
+ self.bump(); // `extern`
  if self.eat_keyword(keywords::Crate) {
  return Ok(Some(self.parse_item_extern_crate(lo, visibility, attrs)?));
  }

src/libsyntax/parse/token.rs

@@ -359,6 +359,7 @@ impl Token {
  Some(id) => id.name == keywords::Super.name() ||
  id.name == keywords::SelfValue.name() ||
  id.name == keywords::SelfType.name() ||
+ id.name == keywords::Extern.name() ||
  id.name == keywords::Crate.name() ||
  id.name == keywords::DollarCrate.name(),
  None => false,

src/test/parse-fail/keyword-extern-as-identifier.rs renamed to src/test/compile-fail/keyword-extern-as-identifier.rs

@@ -8,10 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z parse-only
-
-// This file was auto-generated using 'src/etc/generate-keyword-tests.py extern'
+#![feature(extern_in_paths)]
 
 fn main() {
- let extern = "foo"; //~ error: expected pattern, found keyword `extern`
+ let extern = 0; //~ ERROR expected unit struct/variant or constant, found module `extern`
 }

src/test/compile-fail/rfc-2126-extern-in-paths/auxiliary/xcrate.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[derive(Debug)]
+pub struct S;
+
+#[derive(Debug)]
+pub struct Z;

src/test/compile-fail/rfc-2126-extern-in-paths/non-existent-1.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(extern_in_paths)]
+
+use extern::xcrate::S; //~ ERROR can't find crate for `xcrate`
+
+fn main() {}

src/test/compile-fail/rfc-2126-extern-in-paths/non-existent-2.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(extern_in_paths)]
+
+fn main() {
+ let s = extern::xcrate::S; //~ ERROR can't find crate for `xcrate`
+}

src/test/compile-fail/rfc-2126-extern-in-paths/non-existent-3.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(extern_in_paths)]
+
+use extern::ycrate; //~ ERROR can't find crate for `ycrate`
+
+fn main() {}