Move CrossVersionChecks before FirstTransform

Fixes #17292

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -59,7 +59,8 @@ class Compiler {
   /** Phases dealing with the transformation from pickled trees to backend trees */
   protected def transformPhases: List[List[Phase]] =
     List(new InstrumentCoverage) ::  // Perform instrumentation for code coverage (if -coverage-out is set)
-    List(new FirstTransform,         // Some transformations to put trees into a canonical form
+    List(new CrossVersionChecks,     // Check issues related to deprecated and experimental
+         new FirstTransform,         // Some transformations to put trees into a canonical form
          new CheckReentrant,         // Internal use only: Check that compiled program has no data races involving global vars
          new ElimPackagePrefixes,    // Eliminate references to package prefixes in Select nodes
          new CookComments,           // Cook the comments: expand variables, doc, etc.
@@ -71,8 +72,7 @@ class Compiler {
          new ElimRepeated,           // Rewrite vararg parameters and arguments
          new RefChecks) ::           // Various checks mostly related to abstract members and overriding
     List(new init.Checker) ::        // Check initialization of objects
-    List(new CrossVersionChecks,     // Check issues related to deprecated and experimental
-         new ProtectedAccessors,     // Add accessors for protected members
+    List(new ProtectedAccessors,     // Add accessors for protected members
          new ExtensionMethods,       // Expand methods of value classes with extension methods
          new UncacheGivenAliases,    // Avoid caching RHS of simple parameterless given aliases
          new ElimByName,             // Map by-name parameters to functions

compiler/src/dotty/tools/dotc/typer/CrossVersionChecks.scala

@@ -18,9 +18,6 @@ class CrossVersionChecks extends MiniPhase:
 
   override def description: String = CrossVersionChecks.description
 
-  override def runsAfterGroupsOf: Set[String] = Set(FirstTransform.name)
-    // We assume all type trees except TypeTree have been eliminated
-
   // Note: if a symbol has both @deprecated and @migration annotations and both
   // warnings are enabled, only the first one checked here will be emitted.
   // I assume that's a consequence of some code trying to avoid noise by suppressing
@@ -69,18 +66,8 @@ class CrossVersionChecks extends MiniPhase:
         val since = annot.argumentConstant(1).map(" since " + _.stringValue).getOrElse("")
         report.deprecationWarning(em"${sym.showLocated} is deprecated${since}${msg}", pos)
 
-  private def checkExperimentalSignature(sym: Symbol, pos: SrcPos)(using Context): Unit =
-    class Checker extends TypeTraverser:
-      def traverse(tp: Type): Unit =
-        if tp.typeSymbol.isExperimental then
-          Feature.checkExperimentalDef(tp.typeSymbol, pos)
-        else
-          traverseChildren(tp)
-    if !sym.isInExperimentalScope then
-      new Checker().traverse(sym.info)
-
   private def checkExperimentalAnnots(sym: Symbol)(using Context): Unit =
-    if !sym.isInExperimentalScope then
+    if sym.exists && !sym.isInExperimentalScope then
       for annot <- sym.annotations if annot.symbol.isExperimental do
         Feature.checkExperimentalDef(annot.symbol, annot.tree)
 
@@ -119,13 +106,16 @@ class CrossVersionChecks extends MiniPhase:
   override def transformValDef(tree: ValDef)(using Context): ValDef =
     checkDeprecatedOvers(tree)
     checkExperimentalAnnots(tree.symbol)
-    checkExperimentalSignature(tree.symbol, tree)
     tree
 
   override def transformDefDef(tree: DefDef)(using Context): DefDef =
     checkDeprecatedOvers(tree)
     checkExperimentalAnnots(tree.symbol)
-    checkExperimentalSignature(tree.symbol, tree)
+    tree
+
+  override def transformTypeDef(tree: TypeDef)(using Context): TypeDef =
+    // TODO do we need to check checkDeprecatedOvers(tree)?
+    checkExperimentalAnnots(tree.symbol)
     tree
 
   override def transformIdent(tree: Ident)(using Context): Ident = {
@@ -157,19 +147,14 @@ class CrossVersionChecks extends MiniPhase:
     tree
   }
 
-  override def transformTypeDef(tree: TypeDef)(using Context): TypeDef = {
-    checkExperimentalAnnots(tree.symbol)
+  override def transformOther(tree: Tree)(using Context): Tree =
+    tree.foreachSubTree { // Find references in type trees and imports
+      case tree: Ident => transformIdent(tree)
+      case tree: Select => transformSelect(tree)
+      case tree: TypeTree => transformTypeTree(tree)
+      case _ =>
+    }
     tree
-  }
-
-  override def transformOther(tree: Tree)(using Context): Tree = tree match
-    case tree: Import =>
-      tree.foreachSubTree {
-        case t: RefTree => checkUndesiredProperties(t.symbol, t.srcPos)
-        case _ =>
-      }
-      tree
-    case _ => tree
 
 end CrossVersionChecks
 

tests/neg-custom-args/deprecation/14034b.scala

@@ -9,6 +9,6 @@ type Foo0 = Exp // error
 type Foo = Option[Exp] // error
 type Bar = Option[exp.type] // error
 type Baz = Exp | Int // error
-type Quux = [X] =>> X match // error
-  case Exp => Int
+type Quux = [X] =>> X match
+  case Exp => Int // error
 type Quuz[A <: Exp] = Int // error

tests/neg-custom-args/no-experimental/14034.scala

@@ -7,6 +7,6 @@ type Foo0 = Exp // error
 type Foo = Option[Exp] // error
 type Bar = Option[exp.type] // error
 type Baz = Exp | Int // error
-type Quux = [X] =>> X match // error
-  case Exp => Int
+type Quux = [X] =>> X match
+  case Exp => Int // error
 type Quuz[A <: Exp] = Int // error

tests/neg-custom-args/no-experimental/i17292.scala

@@ -0,0 +1,7 @@
+import annotation.experimental
+
+class Foo { @experimental type Bar = (Int, String) }
+
+val f: Foo = Foo()
+
+def g: Tuple.Elem[f.Bar, 0] = ??? // error

tests/neg-custom-args/no-experimental/i17292b.scala

@@ -0,0 +1,21 @@
+import annotation.experimental
+type A[T] = Int
+class Foo {
+  @experimental type Bar = (Int, String)
+}
+
+type Elem1[X <: Tuple, N <: Int] = X match { case x *: xs => N match { case 0 => x } }
+type Elem2[X <: Tuple, N <: Int]
+
+val f: Foo = Foo()
+
+def bar1: f.Bar = ??? // error
+def bar2 = // error
+  ??? : f.Bar // error
+
+def g0: Elem1[f.Bar, 0] = ??? // error
+def g1(a: Elem1[f.Bar, 0]) = ??? // error
+def g2 =
+  ??? : Elem1[f.Bar, 0] // error
+
+def h: Elem2[f.Bar, 0] = ??? // error