Emit generic signature for static forwarders to nullary methods

Author: lrytz

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

@@ -926,7 +926,7 @@ 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 = 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

tests/pos/i10347/A_1.scala

@@ -0,0 +1,4 @@
+trait L[+T] { def head: T }
+object A {
+  def foo: L[String] = ???
+}

tests/pos/i10347/C_2.java

@@ -0,0 +1,3 @@
+public class C_2 {
+  String hi = A.foo().head();
+}