Refine @TargetNAME hinting

Don't issue the hint of one of the conflicting definitions already
carries a @TargetNAME.

Author: odersky

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

@@ -2079,10 +2079,16 @@ import transform.SymUtils._
             case MethodNotAMethodMatch =>
               "neither has parameters."
             case FullMatch =>
-              i"""have the same$nameAnd type after erasure.
-                 |
-                 |Consider adding a @targetName annotation to one of the conflicting definitions
-                 |for disambiguation."""
+              val hint =
+                if !decl.hasAnnotation(defn.TargetNameAnnot)
+                   && !previousDecl.hasAnnotation(defn.TargetNameAnnot)
+                then
+                  i"""
+                     |
+                     |Consider adding a @targetName annotation to one of the conflicting definitions
+                     |for disambiguation."""
+                else ""
+              i"have the same$nameAnd type after erasure.$hint"
           }
         }
         else ""

tests/neg/override-erasure-clash.check

@@ -5,6 +5,3 @@
   |      def f(): Int in class A at line 3 and
   |      def g(): Int in class B at line 5
   |      have the same name and type after erasure.
-  |
-  |      Consider adding a @targetName annotation to one of the conflicting definitions
-  |      for disambiguation.