Harden copmpareHkApply for ill-typed programs

Turn assertion into test. Without this, neg/tcpoly_overloaded.scala fails.

Author: odersky

src/dotty/tools/dotc/core/TypeComparer.scala

@@ -580,7 +580,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
    */
   def compareHkApply2(tp1: Type, tp2: HKApply, tycon2: Type, args2: List[Type]): Boolean = {
     val tparams = tycon2.typeParams
-    assert(tparams.nonEmpty)
+    if (tparams.isEmpty) return false // can happen for ill-typed programs, e.g. neg/tcpoly_overloaded.scala
 
     /** True if `tp1` and `tp2` have compatible type constructors and their
      *  corresponding arguments are subtypes relative to their variance (see `isSubArgs`).

tests/neg/tcpoly_overloaded.scala

@@ -0,0 +1,25 @@
+trait Monad[T <: Bound[T], MyType[x <: Bound[x]], Bound[_]] {
+  def flatMap[S <: RBound[S], RContainer[x <: RBound[x]], RBound[_],
+              Result[x <: RBound[x]] <: Monad[x, RContainer, RBound]]
+              (f: T => Result[S]): Result[S]
+  def flatMap[S <: RBound[S], RContainer[x <: RBound[x]], RBound[_],
+              Result[x <: RBound[x]] <: Monad[x, RContainer, RBound]]
+              (f: T => Result[S], foo: String): Result[S]
+  def flatMap[S <: Bound[S]]
+              (f: T => MyType[S], foo: Int): MyType[S]
+}
+
+trait Test {
+  def moo: MList[Int]
+  class MList[T](el: T) extends Monad[T, List, Any] {  // error: does not conform to upper bound // error
+    def flatMap[S <: RBound[S], RContainer[x <: RBound[x]], RBound[_],
+            Result[x <: RBound[x]] <: Monad[x, RContainer, RBound]]
+            (f: T => Result[S]): Result[S] = sys.error("foo")
+    def flatMap[S <: RBound[S], RContainer[x <: RBound[x]], RBound[_],
+            Result[x <: RBound[x]] <: Monad[x, RContainer, RBound]]
+            (f: T => Result[S], foo: String): Result[S]  = sys.error("foo")
+    def flatMap[S]
+            (f: T => List[S], foo: Int): List[S]  = sys.error("foo")
+  }
+  val l: MList[String] = moo.flatMap[String, List, Any, MList]((x: Int) => new MList("String")) // error: does not conform to upper bound // error
+}

tests/pending/pos/tcpoly_bounds1.scala renamed to tests/pos/tcpoly_bounds1.scala

@@ -7,7 +7,7 @@ object foo extends Foo[MyPair]
 
 
 trait Monad[m[x <: Bound[x]], Bound[x], a] // TODO: variances!
-trait ListMonad[a] extends Monad[List, Any, a]
+trait ListMonad[a] extends Monad[List, [X] -> Any, a] // Dotty difference: Any is not a legal argument for hk type.
 
 trait MyOrdered[a]
 trait MySet[x <: MyOrdered[x]]

tests/pending/pos/tcpoly_overloaded.scala renamed to tests/pos/tcpoly_overloaded.scala

@@ -11,7 +11,7 @@ trait Monad[T <: Bound[T], MyType[x <: Bound[x]], Bound[_]] {
 
 trait Test {
   def moo: MList[Int]
-  class MList[T](el: T) extends Monad[T, List, Any] {
+  class MList[T](el: T) extends Monad[T, List, [X] -> Any] {
     def flatMap[S <: RBound[S], RContainer[x <: RBound[x]], RBound[_],
             Result[x <: RBound[x]] <: Monad[x, RContainer, RBound]]
             (f: T => Result[S]): Result[S] = sys.error("foo")
@@ -21,5 +21,5 @@ trait Test {
     def flatMap[S]
             (f: T => List[S], foo: Int): List[S]  = sys.error("foo")
   }
-  val l: MList[String] = moo.flatMap[String, List, Any, MList]((x: Int) => new MList("String"))
+  val l: MList[String] = moo.flatMap[String, List, [X] -> Any, MList]((x: Int) => new MList("String"))
 }