Fix #6215: Keep track of levels inside patterns

compiler/src/dotty/tools/dotc/transform/TreeMapWithStages.scala

@@ -108,9 +108,12 @@ abstract class TreeMapWithStages(@constructorOnly ictx: Context) extends TreeMap
           val last = enteredSyms
           // mark all bindings
           new TreeTraverser {
-            def traverse(tree: Tree)(implicit ctx: Context): Unit = {
-              markDef(tree)
-              traverseChildren(tree)
+            def traverse(tree: Tree)(implicit ctx: Context): Unit = tree match {
+              case Quoted(t) => traverse(t)(quoteContext)
+              case Splice(t) => traverse(t)(spliceContext)
+              case _ =>
+                markDef(tree)
+                traverseChildren(tree)
             }
           }.traverse(pat)
           mapOverTree(last)

tests/neg/quotedPatterns-1.scala

@@ -0,0 +1,6 @@
+object Test {
+  def test(x: quoted.Expr[Int]) given tasty.Reflection = x match {
+    case '{ val a = '{ println($y) }; 0 } => ??? // error: Not found: y
+    case _ =>
+  }
+}

tests/neg/quotedPatterns-2.scala

@@ -0,0 +1,6 @@
+object Test {
+  def test(x: quoted.Expr[Int]) given tasty.Reflection = x match {
+    case '{ val a = 4; '{ a }; $y } => y // error: access to value a from wrong staging level
+    case _ =>
+  }
+}

tests/pos/quotedPatterns.scala

@@ -9,6 +9,7 @@ object Test {
     case '{1 + 2} => '{0}
     case '{f($y)} => y
     case '{g($y, $z)} => '{$y * $z}
+    case '{ ((a: Int) => 3)($y) } => y
     case '{ 1 + ($y: Int)} => y
       // currently gives an unreachable case warning
       // but only when used in conjunction with the others.