Fix #2230: Add regression test.

Author: nicolasstucki

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -157,6 +157,8 @@ class CompilationTests extends ParallelSummaryReport with ParallelTesting {
     compileFile("../tests/neg/tailcall/tailrec.scala", defaultOptions) +
     compileFile("../tests/neg/tailcall/tailrec-2.scala", defaultOptions) +
     compileFile("../tests/neg/tailcall/tailrec-3.scala", defaultOptions) +
+    compileFile("../tests/neg/double-bindings/overloadsOnAbstractTypes.scala",
+        defaultOptions.filter(_ != "-Yno-double-bindings")) +
     compileDir("../tests/neg/typedIdents", defaultOptions)
   }.checkExpectedErrors()
 

tests/neg/double-bindings/overloadsOnAbstractTypes.scala

@@ -0,0 +1,22 @@
+
+class Test1 {
+  type A
+  type B <: A
+
+  def foo(): A = ???
+  def foo(): A = ??? // error
+
+  def bar(): A = ???
+  def bar(): B = ??? // error
+}
+
+class Test2 {
+  type A
+  type B <: A
+
+  def foo(x: A) = ???
+  def foo(x: A) = ??? // error
+
+  def bar(x: A) = ???
+  def bar(x: B) = ??? // error
+}