safeDealias for underlyingMatchType

We already dealias the tycon of an applied type for the underlyingMatchType
This generalizes to all TypeRefs

Author: EugeneFlesselle

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -468,7 +468,7 @@ object Types extends TypeUtils {
     /** Does this application expand to a match type? */
     def isMatchAlias(using Context): Boolean = underlyingMatchType.exists
 
-    def underlyingMatchType(using Context): Type = stripped match
+    def underlyingMatchType(using Context): Type = this.safeDealias match
       case tp: MatchType => tp
       case tp: AppliedType => tp.underlyingMatchType
       case _ => NoType

tests/neg/i14834.scala

@@ -1,2 +1,2 @@
-type F[_] = A
-type A = F[?]  // error: cyclic
+type F[_] = A // error: cyclic
+type A = F[?] // error: no wildcard type allowed here

tests/neg/i4368.scala

@@ -154,8 +154,8 @@ object i4369 {
   class Foo extends X { type R = Foo; type Z = Foo }
 }
 object i4370 {
-  class Foo { type R = A }
-  type A = List[Foo#R] // error: cyclic
+  class Foo { type R = A } // error: cyclic
+  type A = List[Foo#R]
 }
 object i4371 {
   class Foo { type A = Boo#B } // error: cyclic

tests/neg/i4370.scala

@@ -1,4 +1,4 @@
 object App {
-  class Foo { type R = A }
-  type A = List[Foo#R] // error
+  class Foo { type R = A } // error
+  type A = List[Foo#R]
 }

tests/neg/toplevel-cyclic/defs_1.scala

@@ -1 +1 @@
-type A = B
+type A = B // error: cyclic

tests/neg/toplevel-cyclic/moredefs_1.scala

@@ -1 +1 @@
-type B = A // error: recursion limit exceeded
+type B = A