Drop normalization of applied match alias arguments

Delay their normalization until it is needed.
Avoids overflows from infinite match types that did not need to normalize.
Also improves MatchTypeTraces as a side effect.

It appears to have been added to avoid some separate issue, which seems to have been fixed.
It is no longer needed since the previous fix with constant folding in disjointnessBoundary.

[Cherry-picked 32752e2][modified]

Author: prolativ

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

@@ -4517,7 +4517,14 @@ object Types extends TypeUtils {
           case MatchAlias(alias) =>
             trace(i"normalize $this", typr, show = true) {
               MatchTypeTrace.recurseWith(this) {
-                alias.applyIfParameterized(args.map(_.normalized)).tryNormalize
+                alias.applyIfParameterized(args).tryNormalize
+                /* `applyIfParameterized` may reduce several HKTypeLambda applications
+                 * before the underlying MatchType is reached.
+                 * Even if they do not involve any match type normalizations yet,
+                 * we still want to record these reductions in the MatchTypeTrace.
+                 * They should however only be attempted if they eventually expand
+                 * to a match type, which is ensured by the `isMatchAlias` guard.
+                 */
               }
             }
           case _ =>

tests/neg/i12049d.check

@@ -0,0 +1,14 @@
+-- [E007] Type Mismatch Error: tests/neg/i12049d.scala:14:52 -----------------------------------------------------------
+14 |val x: M[NotRelevant[Nothing], Relevant[Nothing]] = 2 // error
+   |                                                    ^
+   |                                                  Found:    (2 : Int)
+   |                                                  Required: M[NotRelevant[Nothing], Relevant[Nothing]]
+   |
+   |                                                  Note: a match type could not be fully reduced:
+   |
+   |                                                    trying to reduce  M[NotRelevant[Nothing], Relevant[Nothing]]
+   |                                                    trying to reduce  Relevant[Nothing]
+   |                                                    failed since selector Nothing
+   |                                                    is uninhabited (there are no values of that type).
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg/i12049d.scala

@@ -0,0 +1,14 @@
+
+trait A
+trait B
+
+type M[X, Y] = Y match
+  case A => Int
+  case B => String
+
+type Relevant[Z] = Z match
+  case A => B
+type NotRelevant[Z] = Z match
+  case B => A
+
+val x: M[NotRelevant[Nothing], Relevant[Nothing]] = 2 // error

tests/pos/matchtype-unusedArg/A_1.scala

@@ -0,0 +1,8 @@
+
+type Rec[X] = X match
+  case Int => Rec[X]
+
+type M[Unused, Y] = Y match
+  case String => Double
+
+def foo[X](d: M[Rec[X], "hi"]) = ???

tests/pos/matchtype-unusedArg/B_2.scala

@@ -0,0 +1,2 @@
+
+def Test = foo[Int](3d) // crash before changes