Fix #3323: Add regression test

Author: nicolasstucki

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

@@ -55,6 +55,8 @@ class CompilationTests extends ParallelTesting {
     compileFile("../tests/pos-scala2/rewrites.scala", scala2Mode.and("-rewrite")).copyToTarget() +
     compileFile("../tests/pos-special/utf8encoded.scala", explicitUTF8) +
     compileFile("../tests/pos-special/utf16encoded.scala", explicitUTF16) +
+    compileFile("../tests/pos-special/i3323.scala", defaultOptions.and("-Xfatal-warnings")) +
+    compileFile("../tests/pos-special/i3323b.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("../tests/pos-special/i3589-b.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileList(
       "compileMixed",

tests/pos-special/i3323.scala

@@ -0,0 +1,7 @@
+class Foo {
+  def foo[A](lss: List[List[A]]): Unit = {
+    lss match {
+      case xss: List[List[A]] =>
+    }
+  }
+}

tests/pos-special/i3323b.scala

@@ -0,0 +1,7 @@
+class Foo {
+  def foo(lss: List[Int]): Unit = {
+    lss match {
+      case xss: List[Int] =>
+    }
+  }
+}