Extract GADT constraints from wildcard type arguments

Author: dwijnand

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

@@ -256,12 +256,7 @@ trait PatternTypeConstrainer { self: TypeComparer =>
               val variance = param.paramVarianceSign
               if variance != 0 && !assumeInvariantRefinement then true
               else if argS.isInstanceOf[TypeBounds] || argP.isInstanceOf[TypeBounds] then
-                // Passing TypeBounds to isSubType on LHS or RHS does the
-                // incorrect thing and infers unsound constraints, while simply
-                // returning true is sound. However, I believe that it should
-                // still be possible to extract useful constraints here.
-                // TODO extract GADT information out of wildcard type arguments
-                true
+                isSubType(SkolemType(patternTp), scrutineeTp)
               else {
                 var res = true
                 if variance <  1 then res &&= isSubType(argS, argP)

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -339,14 +339,12 @@ trait ParallelTesting extends RunnerOrchestration { self =>
     }
 
     /** All testSources left after filtering out */
-    private val filteredSources =
-      if (!testFilter.isDefined) testSources
-      else testSources.filter {
-        case JointCompilationSource(_, files, _, _, _, _) =>
-          files.exists(file => file.getPath.contains(testFilter.get))
-        case SeparateCompilationSource(_, dir, _, _) =>
-          dir.getPath.contains(testFilter.get)
+    private val filteredSources = testFilter.map(_.split(',')) match
+      case Some(testFilters) => testSources.filter {
+        case JointCompilationSource(_, files, _, _, _, _) => files.exists(f => testFilters.exists(f.getPath.contains))
+        case SeparateCompilationSource(_, dir, _, _)      => testFilters.exists(dir.getPath.contains)
       }
+      case _ => testSources
 
     /** Total amount of test sources being compiled by this test */
     val sourceCount = filteredSources.length

tests/pos/i13998.scala

@@ -0,0 +1,10 @@
+case class Box[V](value: V)
+object Box:
+  def apply[A](a: A): Box[A]        = new Box[A](a)
+  def unapply[U](b: Box[U]): Box[U] = b
+
+class Test:
+  def value: Box[_ <: String] = Box("text")
+
+  def test: String = value match
+    case Box(text) => text: String