Merge pull request #5178 from Jasper-M/fix/5044

Fix #5044: guard against forward references in the TypeTree of New trees

Author: allanrenucci

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

@@ -1010,9 +1010,14 @@ class RefChecks extends MiniPhase { thisPhase =>
   }
 
   override def transformNew(tree: New)(implicit ctx: Context) = {
-    val sym = tree.tpe.typeSymbol
+    val tpe = tree.tpe
+    val sym = tpe.typeSymbol
     checkUndesiredProperties(sym, tree.pos)
     currentLevel.enterReference(sym, tree.pos)
+    tpe.dealias.foreachPart {
+      case TermRef(_, s: Symbol) => currentLevel.enterReference(s, tree.pos)
+      case _ =>
+    }
     tree
   }
 }
@@ -1643,4 +1648,3 @@ class RefChecks extends MiniPhase { thisPhase =>
       }
     }
 */
-

tests/neg/i5044.scala

@@ -0,0 +1,26 @@
+class I0 {
+  class I1
+  def test0 = {
+    val x = new y.I1 // error: `y` is a forward reference extending over the definition of `x`
+    val y = new I0
+  }
+
+  def test1 = {
+    type T = y.I1
+    val x = new T // error: `y` is a forward reference extending over the definition of `x`
+    val y = new I0
+  }
+
+  class I2[T1, T2]
+  def test2 = {
+    type A[T] = y.I2[T, String]
+    val x = new A[Int] // error: `y` is a forward reference extending over the definition of `x`
+    val y = new I0
+  }
+
+  def test3 = {
+    val x = new T // error: `T` is a forward reference extending over the definition of `x`
+    val y = new I0
+    type T = y.I1
+  }
+}