From 71e7924cb2a52e317c7e009c6dcb69cdaacbb83a Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Wed, 23 Dec 2020 19:47:46 +0100
Subject: [PATCH] Fix #10905: Fix explicitSelf phase

We need to rewire also some references that are simple identifiers.
---
 .../tools/dotc/transform/ExplicitSelf.scala   | 21 ++++++++++++-------
 tests/run/i10905.scala                        |  6 ++++++
 2 files changed, 20 insertions(+), 7 deletions(-)
 create mode 100644 tests/run/i10905.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/ExplicitSelf.scala b/compiler/src/dotty/tools/dotc/transform/ExplicitSelf.scala
index 0d28d71ba22a..3a2bda437d80 100644
--- a/compiler/src/dotty/tools/dotc/transform/ExplicitSelf.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ExplicitSelf.scala
@@ -2,10 +2,7 @@ package dotty.tools.dotc
 package transform
 
 import core._
-import Contexts._
-import Types._
-import MegaPhase._
-import ast.Trees._
+import Contexts._, Types._, MegaPhase._, ast.Trees._, Symbols._, Decorators._, Flags._
 
 /** Transform references of the form
  *
@@ -26,18 +23,28 @@ class ExplicitSelf extends MiniPhase {
 
   override def phaseName: String = "explicitSelf"
 
+  private def needsCast(tree: RefTree, cls: ClassSymbol)(using Context) =
+    !cls.is(Package) && cls.givenSelfType.exists && !cls.derivesFrom(tree.symbol.owner)
+
+  private def castQualifier(tree: RefTree, cls: ClassSymbol, thiz: Tree)(using Context) =
+    cpy.Select(tree)(thiz.cast(AndType(cls.classInfo.selfType, thiz.tpe)), tree.name)
+
   override def transformIdent(tree: Ident)(using Context): Tree = tree.tpe match {
     case tp: ThisType =>
       report.debuglog(s"owner = ${ctx.owner}, context = ${ctx}")
       This(tp.cls).withSpan(tree.span)
-    case _ => tree
+    case TermRef(thisTp: ThisType, _) =>
+      val cls = thisTp.cls
+      if needsCast(tree, cls) then castQualifier(tree, cls, This(cls))
+      else tree
+    case _ =>
+      tree
   }
 
   override def transformSelect(tree: Select)(using Context): Tree = tree match {
     case Select(thiz: This, name) if name.isTermName =>
       val cls = thiz.symbol.asClass
-      if (cls.givenSelfType.exists && !cls.derivesFrom(tree.symbol.owner))
-        cpy.Select(tree)(thiz.cast(AndType(cls.classInfo.selfType, thiz.tpe)), name)
+      if needsCast(tree, cls) then castQualifier(tree, cls, thiz)
       else tree
     case _ => tree
   }
diff --git a/tests/run/i10905.scala b/tests/run/i10905.scala
new file mode 100644
index 000000000000..2637d69cc8a2
--- /dev/null
+++ b/tests/run/i10905.scala
@@ -0,0 +1,6 @@
+class C(val x: Int) extends TypeHelpers
+abstract class TypeHelpers:
+  self: C =>
+  def f = x
+@main def Test =
+  C(0).f