Fix a NSDNHAO in extension methods.

A bridge method, created when we override a method from
a superclass and refine the return type, was appearing
as an overloaded alternative. (`erasure` doesn't create
new scopes, so the bridges it builds are visible at
earlier phases.)

The problem was masked when compiling with specialization,
which *does* create a new scope, shielding the code in
question from the artefacts of erasure.

To fix the problem, we filter out bridge methods from
the overloaded alternatives returned by `.decl`, as would
happen internally in `.member`.

1 files changed, 13 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/ExtensionMethods.scala b/src/compiler/scala/tools/nsc/transform/ExtensionMethods.scala
index 007457ef7b..8556cc9ddc 100644
--- a/src/compiler/scala/tools/nsc/transform/ExtensionMethods.scala
+++ b/src/compiler/scala/tools/nsc/transform/ExtensionMethods.scala
@@ -44,8 +44,18 @@ abstract class ExtensionMethods extends Transform with TypingTransformers {
    *  in `extensionMethod` if the first name has the wrong type. We thereby gain a level of insensitivity
    *  of how overloaded types are ordered between phases and picklings.
    */
-  private def extensionNames(imeth: Symbol): Stream[Name] =
-    imeth.owner.info.decl(imeth.name).tpe match {
+  private def extensionNames(imeth: Symbol): Stream[Name] = {
+    val decl = imeth.owner.info.decl(imeth.name)
+
+    // Bridge generation is done at phase `erasure`, but new scopes are only generated
+    // for the phase after that. So bridges are visible in earlier phases.
+    //
+    // `info.member(imeth.name)` filters these out, but we need to use `decl`
+    // to restrict ourselves to members defined in the current class, so we
+    // must do the filtering here.
+    val declTypeNoBridge = decl.filter(sym => !sym.isBridge).tpe
+
+    declTypeNoBridge match {
       case OverloadedType(_, alts) =>
         val index = alts indexOf imeth
         assert(index >= 0, alts+" does not contain "+imeth)
@@ -55,6 +65,7 @@ abstract class ExtensionMethods extends Transform with TypingTransformers {
         assert(tpe != NoType, imeth.name+" not found in "+imeth.owner+"'s decls: "+imeth.owner.info.decls)
         Stream(newTermName("extension$"+imeth.name))
     }
+  }
 
   /** Return the extension method that corresponds to given instance method `meth`.
    */