SI-8291 Fix implicitNotFound message with type aliases

This pattern of code is typically a bug:

    if (f(tp.typeSymbol)) {
       g(tp.typeArgs)
    }

Intead, one needs to take the base type of `tp` wrt `tp.typeSymbol`.

This commit does exactly that when formatting the `@implicitNotFound`
custom error message.

Patch found on the back of an envelope in the handwriting of @adriaanm

1 files changed, 3 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
index b85c8e6d42..74c28122a1 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala
@@ -1478,8 +1478,10 @@ trait Implicits {
         })
 
       private lazy val typeParamNames: List[String] = sym.typeParams.map(_.decodedName)
+      private def typeArgsAtSym(paramTp: Type) = paramTp.baseType(sym).typeArgs
+
+      def format(paramName: Name, paramTp: Type): String = format(typeArgsAtSym(paramTp) map (_.toString))
 
-      def format(paramName: Name, paramTp: Type): String = format(paramTp.typeArgs map (_.toString))
       def format(typeArgs: List[String]): String =
         interpolate(msg, Map((typeParamNames zip typeArgs): _*)) // TODO: give access to the name and type of the implicit argument, etc?