Merge pull request #3345 from retronym/ticket/8114

[nomaster]  Binary compat. workaround for erasure bug 

1 files changed, 26 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/jvm/GenASM.scala b/src/compiler/scala/tools/nsc/backend/jvm/GenASM.scala
index 19cdcd2590..3712745590 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/GenASM.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/GenASM.scala
@@ -1397,13 +1397,38 @@ abstract class GenASM extends SubComponent with BytecodeWriters with GenJVMASM {
       }
 
       clasz.fields  foreach genField
-      clasz.methods foreach { im => genMethod(im, c.symbol.isInterface) }
+      clasz.methods foreach { im =>
+        if (im.symbol.isBridge && isRedundantBridge(im, clasz))
+          // We can't backport the erasure fix of SI-7120 to 2.10.x, but we can detect and delete
+          // bridge methods with identical signatures to their targets.
+          //
+          // NOTE: this backstop only implemented here in the ASM backend, and is not implemented in the FJBG backend.
+          debugwarn(s"Discarding redundant bridge method: ${im.symbol.debugLocationString}. See SI-8114.")
+        else 
+          genMethod(im, c.symbol.isInterface)
+      }
 
       addInnerClasses(clasz.symbol, jclass)
       jclass.visitEnd()
       writeIfNotTooBig("" + c.symbol.name, thisName, jclass, c.symbol)
     }
 
+    private def isRedundantBridge(bridge: IMethod, owner: IClass): Boolean = {
+      def lastCalledMethod: Option[Symbol] = bridge.code.instructions.reverseIterator.collectFirst {
+        case CALL_METHOD(meth, _) => meth
+      }
+      def hasSameSignatureAsBridge(targetMethod: Symbol): Boolean = {
+        val targetIMethod = clasz.methods find (m => m.symbol == targetMethod)
+        // Important to compare the IMethod#paramss, rather then the erased MethodTypes, as
+        // due to the bug SI-7120, these are out of sync. For example, in the `applyOrElse`
+        // method in run/t8114.scala, the method symbol info has a parameter of type `Long`,
+        // but the IMethod parameter has type `Object`. The latter comes from the info of the
+        // symbol representing the parameter ValDef in the tree, which is incorrectly erased.
+        targetIMethod exists (m => bridge.matchesSignature(m))
+      }
+      lastCalledMethod exists hasSameSignatureAsBridge
+    }
+
     /**
      * @param owner internal name of the enclosing class of the class.
      *