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.

4 files changed, 13 insertions, 9 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
diff --git a/test/files/neg/macro-bundle-polymorphic.check b/test/files/neg/macro-bundle-polymorphic.check
index dc6f540f77..60a4d59119 100644
--- a/test/files/neg/macro-bundle-polymorphic.check
+++ b/test/files/neg/macro-bundle-polymorphic.check
@@ -1,19 +1,19 @@
 macro-bundle-polymorphic.scala:36: error: macro bundles must be concrete monomorphic classes having a single constructor with a `val c: Context` parameter
   def black1: Any = macro BlackboxBundle1.impl
                           ^
-macro-bundle-polymorphic.scala:37: error: not found: value BlackboxBundle2
+macro-bundle-polymorphic.scala:37: error: macro bundles must be concrete monomorphic classes having a single constructor with a `val c: Context` parameter
   def black2: Any = macro BlackboxBundle2.impl
                           ^
-macro-bundle-polymorphic.scala:38: error: not found: value BlackboxBundle3
+macro-bundle-polymorphic.scala:38: error: macro bundles must be concrete monomorphic classes having a single constructor with a `val c: Context` parameter
   def black3: Any = macro BlackboxBundle3.impl
                           ^
 macro-bundle-polymorphic.scala:40: error: macro bundles must be concrete monomorphic classes having a single constructor with a `val c: Context` parameter
   def white1: Any = macro WhiteboxBundle1.impl
                           ^
-macro-bundle-polymorphic.scala:41: error: not found: value WhiteboxBundle2
+macro-bundle-polymorphic.scala:41: error: macro bundles must be concrete monomorphic classes having a single constructor with a `val c: Context` parameter
   def white2: Any = macro WhiteboxBundle2.impl
                           ^
-macro-bundle-polymorphic.scala:42: error: not found: value WhiteboxBundle3
+macro-bundle-polymorphic.scala:42: error: macro bundles must be concrete monomorphic classes having a single constructor with a `val c: Context` parameter
   def white3: Any = macro WhiteboxBundle3.impl
                           ^
 6 errors found
diff --git a/test/files/neg/macro-bundle-wrongcontext-a.check b/test/files/neg/macro-bundle-wrongcontext-a.check
index 7a48dbfd3a..10aadb0035 100644
--- a/test/files/neg/macro-bundle-wrongcontext-a.check
+++ b/test/files/neg/macro-bundle-wrongcontext-a.check
@@ -1,4 +1,4 @@
-macro-bundle-wrongcontext-a.scala:12: error: not found: value Bundle
+macro-bundle-wrongcontext-a.scala:12: error: macro bundles must be concrete monomorphic classes having a single constructor with a `val c: Context` parameter
   def foo: Any = macro Bundle.impl
                        ^
 one error found
diff --git a/test/files/neg/macro-bundle-wrongcontext-b.check b/test/files/neg/macro-bundle-wrongcontext-b.check
index 9c94c3bc34..e9700d379e 100644
--- a/test/files/neg/macro-bundle-wrongcontext-b.check
+++ b/test/files/neg/macro-bundle-wrongcontext-b.check
@@ -1,4 +1,4 @@
-macro-bundle-wrongcontext-b.scala:10: error: not found: value Bundle
+macro-bundle-wrongcontext-b.scala:10: error: macro bundles must be concrete monomorphic classes having a single constructor with a `val c: Context` parameter
   def foo: Any = macro Bundle.impl
                        ^
 one error found