Merge pull request #12710 from lrytz/i10347

Emit generic signature for static forwarders to nullary methods

Author: smarter

compiler/src/dotty/tools/backend/jvm/BCodeHelpers.scala

@@ -26,6 +26,7 @@ import dotty.tools.dotc.core.Types
 import dotty.tools.dotc.core.Types._
 import dotty.tools.dotc.core.TypeErasure
 import dotty.tools.dotc.transform.GenericSignatures
+import dotty.tools.dotc.transform.ElimErasedValueType
 import dotty.tools.io.AbstractFile
 import dotty.tools.dotc.report
 
@@ -926,7 +927,7 @@ trait BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
     // (one that doesn't erase to the actual signature). See run/t3452b for a test case.
 
     val memberTpe = atPhase(erasurePhase) { moduleClass.denot.thisType.memberInfo(sym) }
-    val erasedMemberType = TypeErasure.fullErasure(memberTpe)
+    val erasedMemberType = ElimErasedValueType.elimEVT(TypeErasure.transformInfo(sym, memberTpe))
     if (erasedMemberType =:= sym.denot.info)
       getGenericSignatureHelper(sym, moduleClass, memberTpe).orNull
     else null

compiler/src/dotty/tools/dotc/core/TypeErasure.scala

@@ -697,7 +697,7 @@ class TypeErasure(sourceLanguage: SourceLanguage, semiEraseVCs: Boolean, isConst
             // See doc comment for ElimByName for speculation how we could improve this.
         else
           MethodType(Nil, Nil,
-            eraseResult(sym.info.finalResultType.translateFromRepeated(toArray = sourceLanguage.isJava)))
+            eraseResult(rt.translateFromRepeated(toArray = sourceLanguage.isJava)))
       case tp1: PolyType =>
         eraseResult(tp1.resultType) match
           case rt: MethodType => rt

compiler/src/dotty/tools/dotc/transform/ElimErasedValueType.scala

@@ -13,6 +13,17 @@ import NameKinds.SuperAccessorName
 
 object ElimErasedValueType {
   val name: String = "elimErasedValueType"
+
+  def elimEVT(tp: Type)(using Context): Type = tp match {
+    case ErasedValueType(_, underlying) =>
+      elimEVT(underlying)
+    case tp: MethodType =>
+      val paramTypes = tp.paramInfos.mapConserve(elimEVT)
+      val retType = elimEVT(tp.resultType)
+      tp.derivedLambdaType(tp.paramNames, paramTypes, retType)
+    case _ =>
+      tp
+  }
 }
 
 /** This phase erases ErasedValueType to their underlying type.
@@ -25,6 +36,7 @@ object ElimErasedValueType {
 class ElimErasedValueType extends MiniPhase with InfoTransformer { thisPhase =>
 
   import tpd._
+  import ElimErasedValueType.elimEVT
 
   override def phaseName: String = ElimErasedValueType.name
 
@@ -48,17 +60,6 @@ class ElimErasedValueType extends MiniPhase with InfoTransformer { thisPhase =>
       elimEVT(tp)
   }
 
-  def elimEVT(tp: Type)(using Context): Type = tp match {
-    case ErasedValueType(_, underlying) =>
-      elimEVT(underlying)
-    case tp: MethodType =>
-      val paramTypes = tp.paramInfos.mapConserve(elimEVT)
-      val retType = elimEVT(tp.resultType)
-      tp.derivedLambdaType(tp.paramNames, paramTypes, retType)
-    case _ =>
-      tp
-  }
-
   def transformTypeOfTree(tree: Tree)(using Context): Tree =
     tree.withType(elimEVT(tree.tpe))
 

tests/pos/i10347/A_1.scala

@@ -0,0 +1,7 @@
+trait L[+T] { def head: T }
+class K(val s: String) extends AnyVal
+object A {
+  def foo: L[String] = ???
+  def bar: L[K] = ???
+  def baz(k: K): L[String] = ???
+}

tests/pos/i10347/C_2.java

@@ -0,0 +1,5 @@
+public class C_2 {
+  String hi = A.foo().head();
+  String hy = A.bar().head();
+  String hj = A.baz("").head();
+}