rustc: Add support for `extern crate foo as bar`

The compiler will now issue a warning for crates that have syntax of the form
`extern crate "foo" as bar`, but it will still continue to accept this syntax.
Additionally, the string `foo-bar` will match the crate name `foo_bar` to assist
in the transition period as well.

This patch will land hopefully in tandem with a Cargo patch that will start
translating all crate names to have underscores instead of hyphens.

cc #23533

1 files changed, 6 insertions, 0 deletions

diff --git a/src/libsyntax/parse/obsolete.rs b/src/libsyntax/parse/obsolete.rs
index 7da0a6de547..276be73823a 100644
--- a/src/libsyntax/parse/obsolete.rs
+++ b/src/libsyntax/parse/obsolete.rs
@@ -24,6 +24,7 @@ use ptr::P;
 pub enum ObsoleteSyntax {
     ClosureKind,
     EmptyIndex,
+    ExternCrateString,
 }
 
 pub trait ParserObsoleteMethods {
@@ -56,6 +57,11 @@ impl<'a> ParserObsoleteMethods for parser::Parser<'a> {
                 "write `[..]` instead",
                 false, // warning for now
             ),
+            ObsoleteSyntax::ExternCrateString => (
+                "\"crate-name\"",
+                "use an identifier not in quotes instead",
+                false, // warning for now
+            ),
         };
 
         self.report(sp, kind, kind_str, desc, error);