Fix ClassElement.allSupertypes to include interfaces of mixins (issue 29767)

pkg/analyzer/lib/src/dart/element/element.dart

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 2379185a61a6ce8e5960b94b2c6268af82f45187..cc8211f2d89c4dd2a1dc0e203de9793d9ea6fef1 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -1154,13 +1154,16 @@ class ClassElementImpl extends AbstractClassElementImpl
         if (supertype != null) {
           typesToVisit.add(supertype);
         }
-        for (InterfaceType type in currentElement.interfaces) {
+        for (InterfaceType type in currentType.interfaces) {

[Jennifer Messerly, 2017/08/17 21:57:29]

oh wow, nice catch!

           typesToVisit.add(type);
         }
-        for (InterfaceType type in currentElement.mixins) {
+        for (InterfaceType type in currentType.mixins) {
           ClassElement element = type.element;
           if (!visitedClasses.contains(element)) {
             supertypes.add(type);
+            for (InterfaceType type in type.interfaces) {

[Jennifer Messerly, 2017/08/17 21:57:29]

there's also the weird case where a mixin's mixin is considered part of its
superclass:


class M1 { m() => print('M1.m()'); }

// this only works when M2 is declared with ClassTypeAlias syntax,
// and it mixes in exactly one other mixin
class M2 = Object with M1;

class B { m() => print('B.m()'); }
class C extends B with M2 {} // M2 is a legal mixin, strangely

main() {
  new C().m(); // prints M1.m
}

[Brian Wilkerson, 2017/08/17 22:49:25]

Is it still the case that classes used as mixins can only extend Object? If not,
does the superclass of the mixin need to be included in this list?

If the answer to either is "yes", then I think the for loop on line 1160 can be
replaced by

for (InterfaceType type in currentType.mixins) {
  typesToVisit.add(type);
}

[Jennifer Messerly, 2017/08/17 23:14:39]

oh yeah, good call! yeah with super mixins, the superclass of the mixin would be
considered as part of the `all supertypes` as well

+              typesToVisit.add(type);
+            }
           }
         }
       }