Ensure type correctness in the presence of This -> proxy mappings

Author: odersky

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

@@ -450,8 +450,7 @@ class Inliner(call: tpd.Tree, rhs: tpd.Tree)(implicit ctx: Context) {
 
     // The tree map to apply to the inlined tree. This maps references to this-types
     // and parameters to references of their arguments or their proxies.
-    def treeMap(tree: Tree) = {
-      tree match {
+    def treeMap(tree: Tree) = tree match {
       case _: This =>
         tree.tpe match {
           case thistpe: ThisType =>
@@ -468,7 +467,7 @@ class Inliner(call: tpd.Tree, rhs: tpd.Tree)(implicit ctx: Context) {
           case None => tree
         }
       case _ => tree
-    }}
+    }
 
     val inlineCtx = inlineContext(call)
     // The complete translation maps references to `this` and parameters to
@@ -519,9 +518,10 @@ class Inliner(call: tpd.Tree, rhs: tpd.Tree)(implicit ctx: Context) {
    *  5. Make sure that the tree's typing is idempotent (so that future -Ycheck passes succeed)
    */
   private object InlineTyper extends ReTyper {
-
     var retainedClosures = Set[Symbol]()
 
+    private val bindings = bindingsBuf.map(_.symbol)
+
     override def typedIdent(tree: untpd.Ident, pt: Type)(implicit ctx: Context) = {
       val tree1 = super.typedIdent(tree, pt)
       tree1 match {
@@ -559,5 +559,18 @@ class Inliner(call: tpd.Tree, rhs: tpd.Tree)(implicit ctx: Context) {
       case _ =>
         super.typedApply(tree, pt)
     }
+
+    /** If expected type contans a reference rooted in a this-proxy,
+     *  the tree's type might still be a subtype of the same reference, but
+     *  rooted in the original `this`. In this case we insert a cast to ensure
+     *  the inlined code is type correct.
+     */
+    override def adaptInterpolated(tree: Tree, pt: Type)(implicit ctx: Context) = {
+      def refersToProxy(tr: NamedType) = tr.isTerm && bindings.contains(tr.symbol)
+      val casted =
+        if (tree.isType || pt.namedPartsWith(refersToProxy).isEmpty) tree
+        else tree.ensureConforms(pt)
+      super.adaptInterpolated(casted, pt)
+    }
   }
 }

tests/pos/i3130b.scala

@@ -1,5 +1,5 @@
-trait F { def f(): Int }
 class Outer {
+  trait F { def f(): Int }
   inline def inner: F = {
     class InnerClass(x: Int) extends F {
       def this() = this(3)