Merge pull request #4948 from szeiger/issue/9574

SI-9574 Prevent illegal overrides of members with module types

2 files changed, 20 insertions, 1 deletions

diff --git a/test/files/neg/override-object-no.check b/test/files/neg/override-object-no.check
index 9cfda80fc3..972a719b3b 100644
--- a/test/files/neg/override-object-no.check
+++ b/test/files/neg/override-object-no.check
@@ -20,4 +20,12 @@ an overriding object must conform to the overridden object's class bound;
  required: case2.Bar[Traversable[String]]
     override object A extends Bar[List[String]]  // err
                     ^
-four errors found
+override-object-no.scala:52: error: overriding method x in trait A of type => SI9574.Foo.type;
+ method x has incompatible type
+  trait B extends A { def x: Bar.type } // should not compile (SI-9574)
+                          ^
+override-object-no.scala:53: error: overriding method x in trait A of type => SI9574.Foo.type;
+ object x has incompatible type
+  trait C extends A { override object x }
+                                      ^
+6 errors found
diff --git a/test/files/neg/override-object-no.scala b/test/files/neg/override-object-no.scala
index 745cdb2332..517408886d 100644
--- a/test/files/neg/override-object-no.scala
+++ b/test/files/neg/override-object-no.scala
@@ -43,3 +43,14 @@ package case2 {
     override object A extends Bar[List[String]]  // err
   }
 }
+
+// Both overridden and overriding members must be objects, not vals with a module type
+object SI9574 {
+  object Foo
+  object Bar
+  trait A { def x: Foo.type }
+  trait B extends A { def x: Bar.type } // should not compile (SI-9574)
+  trait C extends A { override object x }
+  trait D { object x; def y = x }
+  trait E extends D { override val x: super.x.type = y } // OK but doesn't need object subtyping exception
+}