resolve: Support aliasing local crate root in extern prelude

2 files changed, 8 insertions, 1 deletions

diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 2402de5a816..d0c4d1c7dce 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -492,6 +492,9 @@ declare_features! (
 
     // `reason = ` in lint attributes and `expect` lint attribute
     (active, lint_reasons, "1.31.0", Some(54503), None),
+
+    // `extern crate self as foo;` puts local crate root into extern prelude under name `foo`.
+    (active, extern_crate_self, "1.31.0", Some(54658), None),
 );
 
 declare_features! (
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index f13bb7df0b4..33715f206de 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -6783,7 +6783,11 @@ impl<'a> Parser<'a> {
         let error_msg = "crate name using dashes are not valid in `extern crate` statements";
         let suggestion_msg = "if the original crate name uses dashes you need to use underscores \
                               in the code";
-        let mut ident = self.parse_ident()?;
+        let mut ident = if self.token.is_keyword(keywords::SelfValue) {
+            self.parse_path_segment_ident()
+        } else {
+            self.parse_ident()
+        }?;
         let mut idents = vec![];
         let mut replacement = vec![];
         let mut fixed_crate_name = false;