Use a TreeTraverser to check applied types

Author: TheElectronWill

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

@@ -71,7 +71,7 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
   override def run(using Context): Unit =
     val unit = ctx.compilationUnit
     if unit.isJava then
-      checkAppliedTypes(unit.tpdTree)
+      AppliedTypeChecker().traverse(unit.tpdTree)
     else
       super.run
 
@@ -126,34 +126,18 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
           tree
   end normalizeTypeArgs
 
-  /** Scan a tree and check all the AppliedTypeTrees in it. */
-  def checkAppliedTypes(tree: Tree)(using Context): Unit = tree match
-    case tpt: TypeTree =>
-      Checking.checkAppliedTypesIn(tpt)
-    case tree: AppliedTypeTree =>
-      Checking.checkAppliedType(tree, EmptyTree)
-    case tree: TypeBoundsTree =>
-      checkAppliedTypes(tree.hi)
-    case tree: TypeApply =>
-      val TypeApply(fn, args) = normalizeTypeArgs(tree)
-      args.foreach(checkAppliedTypes)
-    case tree: ValDef =>
-      checkAppliedTypes(tree.tpt)
-    case tree: DefDef =>
-      checkAppliedTypes(tree.tpt)
-      tree.vparamss.flatten.foreach(checkAppliedTypes)
-      tree.tparams.foreach(checkAppliedTypes)
-    case PackageDef(pid, stats) =>
-      stats.foreach(checkAppliedTypes)
-    case TypeDef(name, rhs) =>
-      checkAppliedTypes(rhs)
-    case t: Template =>
-      t.parents.foreach(checkAppliedTypes)
-      t.body.foreach(checkAppliedTypes)
-    case a: Annotated =>
-      checkAppliedTypes(a.arg)
-    case _ =>
-      // no need to check this
+  private class AppliedTypeChecker extends TreeTraverser {
+    /** Scan a tree and check all the AppliedTypeTrees in it. */
+    def traverse(tree: Tree)(using Context): Unit = tree match
+      case tpt: TypeTree =>
+        Checking.checkAppliedTypesIn(tpt)
+      case tree: AppliedTypeTree =>
+        Checking.checkAppliedType(tree, EmptyTree)
+      case tree: TypeApply =>
+        traverseChildren(normalizeTypeArgs(tree))
+      case _ =>
+        traverseChildren(tree)
+  }
 
   class PostTyperTransformer extends Transformer {