more helpful bundle error messages

At the moment, bundle selection mechanism is pretty picky. If a candidate
bundle's parameter isn't either blackbox.Context, whitebox.Context or
PrefixType refinement thereof, then it's not a bundle and the user
will get a generic error.

However we can be a bit more helpful and admit classes that are almost
like bundles (looksLikeMacroBundleType), have them fail isMacroBundleType,
and then emit a much prettier error message to the user that would tell them
that bundles must be monomorphic and their sole parameter should not just
be any subtype of blackbox.Context or whitebox.Context.

1 files changed, 7 insertions, 3 deletions

diff --git a/src/reflect/scala/reflect/internal/Definitions.scala b/src/reflect/scala/reflect/internal/Definitions.scala
index 62e98829b7..558e1aa611 100644
--- a/src/reflect/scala/reflect/internal/Definitions.scala
+++ b/src/reflect/scala/reflect/internal/Definitions.scala
@@ -609,8 +609,12 @@ trait Definitions extends api.StandardDefinitions {
     private def macroBundleParamInfo(tp: Type) = {
       val ctor = tp.erasure.typeSymbol.primaryConstructor
       ctor.paramss match {
-        case List(List(c)) => if (isMacroContextType(c.info)) c.info else NoType
-        case _ => NoType
+        case List(List(c)) =>
+          val sym = c.info.typeSymbol
+          val isContextCompatible = sym.isNonBottomSubClass(BlackboxContextClass) || sym.isNonBottomSubClass(WhiteboxContextClass)
+          if (isContextCompatible) c.info else NoType
+        case _ =>
+          NoType
       }
     }
 
@@ -619,7 +623,7 @@ trait Definitions extends api.StandardDefinitions {
 
     def isMacroBundleType(tp: Type) = {
       val isMonomorphic = tp.typeSymbol.typeParams.isEmpty
-      val isContextCompatible = macroBundleParamInfo(tp) != NoType
+      val isContextCompatible = isMacroContextType(macroBundleParamInfo(tp))
       val hasSingleConstructor = !tp.declaration(nme.CONSTRUCTOR).isOverloaded
       val nonAbstract = !tp.erasure.typeSymbol.isAbstractClass
       isMonomorphic && isContextCompatible && hasSingleConstructor && nonAbstract