Emit a warning if a user tries to define

their own subclass of ClassfileAnnotation

2 files changed, 11 insertions, 0 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 1ef6b935e7..c608617ce0 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -1013,6 +1013,11 @@ trait Typers { self: Analyzer =>
       val impl1 = newTyper(context.make(cdef.impl, clazz, scopeFor(cdef.impl)))
         .typedTemplate(cdef.impl, parentTypes(cdef.impl))
       val impl2 = addSyntheticMethods(impl1, clazz, context)
+      if (clazz isNonBottomSubClass ClassfileAnnotationClass)
+	unit.warning (cdef.pos,
+          "implementation restriction: subclassing Classfile does not\n"+
+          "make your annotation visible at runtime.  If that is what\n"+
+	  "you want, you must write the annotation class in Java.")
       copy.ClassDef(cdef, typedMods, cdef.name, tparams1, impl2)
         .setType(NoType)
     }
diff --git a/test/files/neg/annot-nonconst.check b/test/files/neg/annot-nonconst.check
index 197ff930a5..ef1a72adf2 100644
--- a/test/files/neg/annot-nonconst.check
+++ b/test/files/neg/annot-nonconst.check
@@ -1,4 +1,10 @@
+annot-nonconst.scala:1: warning: implementation restriction: subclassing Classfile does not
+make your annotation visible at runtime.  If that is what
+you want, you must write the annotation class in Java.
+class Length(n: Int) extends ClassfileAnnotation
+      ^
 annot-nonconst.scala:5: error: attribute argument needs to be a constant; found: Test.this.n
   @Length(n) def foo = "foo"
           ^
+one warning found
 one error found