Print erased type in double definition message

Print erased type if the message says "have the same type after erasure"

Author: odersky

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -2128,6 +2128,7 @@ import transform.SymUtils._
   class DoubleDefinition(decl: Symbol, previousDecl: Symbol, base: Symbol)(using Context) extends NamingMsg(DoubleDefinitionID) {
     def msg = {
       def nameAnd = if (decl.name != previousDecl.name) " name and" else ""
+      def erasedType = if ctx.erasedTypes then i" ${decl.info}" else ""
       def details(using Context): String =
         if (decl.isRealMethod && previousDecl.isRealMethod) {
           import Signature.MatchDegree._
@@ -2155,7 +2156,7 @@ import transform.SymUtils._
                      |Consider adding a @targetName annotation to one of the conflicting definitions
                      |for disambiguation."""
                 else ""
-              i"have the same$nameAnd type after erasure.$hint"
+              i"have the same$nameAnd type$erasedType after erasure.$hint"
           }
         }
         else ""

tests/neg/i14966a.check

@@ -0,0 +1,10 @@
+-- [E120] Naming Error: tests/neg/i14966a.scala:3:6 --------------------------------------------------------------------
+3 |  def f(x: List[Int]): String = ??? // error
+  |      ^
+  |      Double definition:
+  |      def f[X <: String](x: List[X]): String in class Test at line 2 and
+  |      def f(x: List[Int]): String in class Test at line 3
+  |      have the same type (x: scala.collection.immutable.List): String after erasure.
+  |
+  |      Consider adding a @targetName annotation to one of the conflicting definitions
+  |      for disambiguation.

tests/neg/i14966a.scala

@@ -0,0 +1,4 @@
+class Test:
+  def f[X <: String](x: List[X]): String = ???
+  def f(x: List[Int]): String = ??? // error
+