Improving error message.

Hacked filename into message to alleviate meaningless
"_$1 defined twice" error condition.  References SI-4893.

1 files changed, 15 insertions, 5 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala b/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala
index ea5223e32f..140df53816 100644
--- a/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala
@@ -624,11 +624,21 @@ trait ContextErrors {
         setError(tree)
       }
 
-    // checkNoDoubleDefs...
-      def DefDefinedTwiceError(sym0: Symbol, sym1: Symbol) =
-        issueSymbolTypeError(sym0, sym1+" is defined twice"+
-                                   {if(!settings.debug.value) "" else " in "+context0.unit}+
-                                   {if (sym0.isMacro && sym1.isMacro) " \n(note that macros cannot be overloaded)" else ""})
+      // checkNoDoubleDefs...
+      // @PP: I hacked the filename in (context0.unit) to work around SI-4893.  It would be
+      // much better if every symbol could offer some idea of where it came from, else
+      // the obviously untrue claim that something has been defined twice can only frustrate.
+      // There's no direct test because partest doesn't work, but to reproduce, separately
+      // compile the next two lines:
+      //    package object foo { val x: Class[_] = null }
+      //    package foo
+      def DefDefinedTwiceError(sym0: Symbol, sym1: Symbol) = {
+        val isBug = sym0.isAbstractType && sym1.isAbstractType && (sym0.name startsWith "_$")
+        issueSymbolTypeError(sym0, sym1+" is defined twice in " + context0.unit
+          + ( if (sym0.isMacro && sym1.isMacro) "\n(note that macros cannot be overloaded)" else "" )
+          + ( if (isBug) "\n(this error is likely due to a bug in the scala compiler involving wildcards in package objects)" else "" )
+        )
+      }
 
       // cyclic errors
      def CyclicAliasingOrSubtypingError(errPos: Position, sym0: Symbol) =