Revert "Stop generating generic signatures for mixin forwarders"

lrytz · lrytz · commit 6fc2202a1e5a · 2019-05-06T13:23:23.000+02:00
This reverts commit 162647c.
diff --git a/src/compiler/scala/tools/nsc/transform/Mixin.scala b/src/compiler/scala/tools/nsc/transform/Mixin.scala
@@ -169,7 +169,33 @@ abstract class Mixin extends Transform with ast.TreeDSL with AccessorSynthesis {
     clazz.info.decls enter member setFlag MIXEDIN resetFlag JAVA_DEFAULTMETHOD
   }
   def cloneAndAddMember(mixinClass: Symbol, mixinMember: Symbol, clazz: Symbol): Symbol =
-    addMember(clazz, mixinMember.cloneSymbol(clazz).setFlag(BRIDGE))
+    addMember(clazz, cloneBeforeErasure(mixinClass, mixinMember, clazz).setFlag(BRIDGE))
+
+  def cloneBeforeErasure(mixinClass: Symbol, mixinMember: Symbol, clazz: Symbol): Symbol = {
+    val newSym = enteringErasure {
+      // since we used `mixinMember` from the interface that represents the trait that's
+      // being mixed in, have to instantiate the interface type params (that may occur in mixinMember's
+      // info) as they are seen from the class.  We can't use the member that we get from the
+      // implementation class, as it's a clone that was made after erasure, and thus it does not
+      // know its info at the beginning of erasure anymore.
+      val sym = mixinMember cloneSymbol clazz
+
+      val erasureMap = erasure.erasure(mixinMember)
+      val erasedInterfaceInfo: Type = erasureMap(mixinMember.info)
+      val specificForwardInfo       = (clazz.thisType baseType mixinClass) memberInfo mixinMember
+      val forwarderInfo =
+        if (erasureMap(specificForwardInfo) =:= erasedInterfaceInfo)
+          specificForwardInfo
+        else {
+          erasedInterfaceInfo
+        }
+      // Optimize: no need if mixinClass has no typeparams.
+      // !!! JZ Really? What about the effect of abstract types, prefix?
+      if (mixinClass.typeParams.isEmpty) sym
+      else sym modifyInfo (_ => forwarderInfo)
+    }
+    newSym
+  }
 
   def publicizeTraitMethods(clazz: Symbol): Unit = {
     if (treatedClassInfos(clazz) != clazz.info) {
diff --git a/test/files/neg/t5148.check b/test/files/neg/t5148.check
@@ -1,6 +1,6 @@
-t5148.scala:4: error: Symbol 'type scala.tools.nsc.interpreter.IMain.Request' is missing from the classpath.
+t5148.scala:4: error: Symbol 'term scala.tools.nsc.interpreter.IMain.memberHandlers' is missing from the classpath.
 This symbol is required by 'method scala.tools.nsc.interpreter.Imports.allReqAndHandlers'.
-Make sure that type Request is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
+Make sure that term memberHandlers is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
 A full rebuild may help if 'Imports.class' was compiled against an incompatible version of scala.tools.nsc.interpreter.IMain.
 class IMain extends Imports
             ^

Original file line number	Diff line number	Diff line change
`@@ -1,6 +1,6 @@`
`1`		`-t5148.scala:4: error: Symbol 'type scala.tools.nsc.interpreter.IMain.Request' is missing from the classpath.`
	`1`	`+t5148.scala:4: error: Symbol 'term scala.tools.nsc.interpreter.IMain.memberHandlers' is missing from the classpath.`
`2`	`2`	`This symbol is required by 'method scala.tools.nsc.interpreter.Imports.allReqAndHandlers'.`
`3`		-Make sure that type Request is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
	`3`	+Make sure that term memberHandlers is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
`4`	`4`	`A full rebuild may help if 'Imports.class' was compiled against an incompatible version of scala.tools.nsc.interpreter.IMain.`
`5`	`5`	`class IMain extends Imports`
`6`	`6`	`^`