TEST: Print diffs with previous inference

Author: odersky

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -1507,10 +1507,13 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
               if knownFormal && !formal.isExactlyNothing then
                 formal
               else
-                inferredFromTarget(param, formal, calleeType, paramIndex).orElse(
-                  if knownFormal then formal
-                  else errorType(AnonymousFunctionMissingParamType(param, tree, formal), param.srcPos)
-                )
+                val fromTarget = inferredFromTarget(param, formal, calleeType, paramIndex)
+                if fromTarget.exists then
+                  if knownFormal && (fromTarget ne formal) then
+                    println(i"DIFF for param $i of $tree with pt = $pt, formal = $formal, from target = $fromTarget")
+                  fromTarget
+                else if knownFormal then formal
+                else errorType(AnonymousFunctionMissingParamType(param, tree, formal), param.srcPos)
             val paramTpt = untpd.TypedSplice(
                 (if knownFormal then InferredTypeTree() else untpd.TypeTree())
                   .withType(paramType.translateFromRepeated(toArray = false))