Merge pull request #10760 from lrytz/t12987

Normalize reference to undet param in stabilizer

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -5524,7 +5524,12 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
               context.pendingStabilizers ::= vdef
               qual.changeOwner(context.owner -> vsym)
               val newQual = Ident(vsym) setType singleType(NoPrefix, vsym) setPos qual.pos.focus
-              return typedSelect(tree, newQual, name)
+              return typedSelect(tree, newQual, name).modifyType(_.map {
+                // very specific fix for scala/bug#12987 (details in the ticket)
+                case t: AliasTypeRef if t.pre.termSymbol == vsym && context.undetparams.contains(t.normalize.typeSymbol) =>
+                  t.normalize
+                case t => t
+              })
             }
 
             val tree1 = tree match {

test/files/pos/t12987.scala

@@ -0,0 +1,30 @@
+object typeMember {
+  class Foo {
+    type FT
+    class I
+    def m(b: FT, o: Option[I]): Int = 0
+  }
+
+  object Test {
+    def f[T]: Foo { type FT = T } = ???
+    def t = {
+      val b: Any = ???
+      f.m(b, None)
+    }
+  }
+}
+
+object typeParam {
+  class Foo[FT] {
+    class I
+    def m(b: FT, o: Option[I]): Int = 0
+  }
+
+  object Test {
+    def f[T]: Foo[T] = ???
+    def t = {
+      val b: Any = ???
+      f.m(b, None)
+    }
+  }
+}