Handle self types that are aliases of capturing types

Author: odersky

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -4999,9 +4999,9 @@ object Types {
           if (!givenSelf.isValueType) appliedRef
           else if (clsd.is(Module)) givenSelf
           else if (ctx.erasedTypes) appliedRef
-          else givenSelf match
-            case givenSelf @ EventuallyCapturingType(tp, _) =>
-              givenSelf.derivedAnnotatedType(tp & appliedRef, givenSelf.annot)
+          else givenSelf.dealiasKeepAnnots match
+            case givenSelf1 @ EventuallyCapturingType(tp, _) =>
+              givenSelf1.derivedAnnotatedType(tp & appliedRef, givenSelf1.annot)
             case _ =>
               AndType(givenSelf, appliedRef)
         }

tests/pos-custom-args/captures/selftype-alias.scala

@@ -0,0 +1,9 @@
+import language.experimental.captureChecking
+
+type AnyIterableOnce[A] = IterableOnce[A]^
+
+/** Iterator can be used only once */
+trait IterableOnce[+A]:
+  //this: IterableOnce[A]{ref any} =>
+  this: AnyIterableOnce[A] =>
+  def iterator: Iterator[A]^{this}