Allow super calls in mixin declarations

Allow super calls to occur in mixin declarations if they target a
method from any of the superclass constraint interfaces.

Instead of compiling the Dart mixin declaration
    mixin M on S0, S1 {...}
to Kernel:
    abstract class _M&S0&S1 = S0 with S1;
    abstract class M extends _M&S0&S1 { ... }
we compile it to Kernel:
    abstract class _M&S0&S1 implements S0, S1 {}
    abstract class M extends _M&S0&S1 { ... }
because the former is not symmetrical with respect to S0 and S1.  It
will prefer a method from the 'mixin' S1 over one from S0 which can
give a compile-time error if the method from S0 is more general.

Modify mixin inference to support the new compilation of mixin
declarations.  It still has to support old-style VM super mixins until
support for those is removed from the VM.

Change-Id: Ib945aa11cc19c457b07bc802beae10d1663ff6b7
Reviewed-on: https://dart-review.googlesource.com/76141
Reviewed-by: Jenny Messerly <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>
Reviewed-by: Dmitry Stefantsov <[email protected]>
Commit-Queue: Kevin Millikin <[email protected]>

Author: Kevin Millikin

pkg/compiler/lib/src/kernel/element_map_impl.dart

@@ -289,44 +289,7 @@ abstract class KernelToElementMapBase implements IrToElementMap {
         InterfaceType supertype;
         LinkBuilder<InterfaceType> linkBuilder =
             new LinkBuilder<InterfaceType>();
-        if (node.isMixinDeclaration) {
-          // A mixin declaration
-          //
-          //   mixin M on A, B, C {}
-          //
-          // is encoded by CFE as
-          //
-          //   abstract class M extends A with B, C {}
-          //
-          // but we encode it as
-          //
-          //   abstract class M extends Object implements A, B, C {}
-          //
-          // so we need to collect the non-Object superclasses and add them
-          // to the interfaces of M.
-
-          ir.Class superclass = node.superclass;
-          while (superclass != null) {
-            if (superclass.isAnonymousMixin) {
-              // Add second to last mixed in superclasses. `B` and `C` in the
-              // example above.
-              ir.DartType mixinType = typeEnvironment.hierarchy
-                  .getTypeAsInstanceOf(node.thisType, superclass.mixedInClass);
-              linkBuilder.addLast(getDartType(mixinType));
-            } else {
-              // Add first mixed in superclass. `A` in the example above.
-              ir.DartType mixinType = typeEnvironment.hierarchy
-                  .getTypeAsInstanceOf(node.thisType, superclass);
-              linkBuilder.addLast(getDartType(mixinType));
-              break;
-            }
-            superclass = superclass.superclass;
-          }
-          // Set superclass to `Object`.
-          supertype = _commonElements.objectType;
-        } else {
-          supertype = processSupertype(node.supertype);
-        }
+        supertype = processSupertype(node.supertype);
         if (supertype == _commonElements.objectType) {
           ClassEntity defaultSuperclass =
               _commonElements.getDefaultSuperclass(cls, nativeBasicData);

pkg/dev_compiler/lib/src/kernel/kernel_helpers.dart

@@ -230,7 +230,8 @@ Class getSuperclassAndMixins(Class c, List<Class> mixins) {
 
   var sc = c.superclass;
   for (; sc.isAnonymousMixin; sc = sc.superclass) {
-    mixins.add(sc.mixedInClass);
+    mixedInClass = sc.mixedInClass;
+    if (mixedInClass != null) mixins.add(sc.mixedInClass);
   }
   return sc;
 }

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -1494,11 +1494,12 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     Member target = isSuper
         ? hierarchy.getDispatchTarget(cls, name, setter: isSetter)
         : hierarchy.getInterfaceMember(cls, name, setter: isSetter);
-    if (isSuper &&
-        target == null &&
-        library.loader.target.backendTarget.enableSuperMixins &&
-        classBuilder.isAbstract) {
-      target = hierarchy.getInterfaceMember(cls, name, setter: isSetter);
+    if (isSuper && target == null) {
+      if (classBuilder.cls.isMixinDeclaration ||
+          (library.loader.target.backendTarget.enableSuperMixins &&
+              classBuilder.isAbstract)) {
+        target = hierarchy.getInterfaceMember(cls, name, setter: isSetter);
+      }
     }
     return target;
   }

pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart

@@ -231,7 +231,7 @@ class KernelLibraryBuilder
         modifiers,
         className,
         typeVariables,
-        applyMixins(supertype, supertypeOffset, className,
+        applyMixins(supertype, supertypeOffset, className, isMixinDeclaration,
             typeVariables: typeVariables),
         interfaces,
         classScope,
@@ -307,8 +307,8 @@ class KernelLibraryBuilder
     return typeVariablesByName;
   }
 
-  KernelTypeBuilder applyMixins(
-      KernelTypeBuilder type, int charOffset, String subclassName,
+  KernelTypeBuilder applyMixins(KernelTypeBuilder type, int charOffset,
+      String subclassName, bool isMixinDeclaration,
       {String documentationComment,
       List<MetadataBuilder> metadata,
       String name,
@@ -469,8 +469,10 @@ class KernelLibraryBuilder
                 : abstractMask,
             fullname,
             applicationTypeVariables,
-            supertype,
-            isNamedMixinApplication ? interfaces : null,
+            isMixinDeclaration ? null : supertype,
+            isNamedMixinApplication
+                ? interfaces
+                : isMixinDeclaration ? [supertype, mixin] : null,
             new Scope(<String, MemberBuilder>{}, <String, MemberBuilder>{},
                 scope.withTypeVariables(typeVariables),
                 "mixin $fullname ", isModifiable: false),
@@ -481,7 +483,7 @@ class KernelLibraryBuilder
             startCharOffset,
             charOffset,
             TreeNode.noOffset,
-            mixedInType: mixin);
+            mixedInType: isMixinDeclaration ? null : mixin);
         if (isNamedMixinApplication) {
           loader.target.metadataCollector?.setDocumentationComment(
               application.target, documentationComment);
@@ -512,7 +514,7 @@ class KernelLibraryBuilder
     // Nested declaration began in `OutlineBuilder.beginNamedMixinApplication`.
     endNestedDeclaration(name).resolveTypes(typeVariables, this);
     KernelNamedTypeBuilder supertype = applyMixins(
-        mixinApplication, charOffset, name,
+        mixinApplication, charOffset, name, false,
         documentationComment: documentationComment,
         metadata: metadata,
         name: name,

pkg/front_end/lib/src/fasta/source/source_loader.dart

@@ -30,8 +30,6 @@ import 'package:kernel/class_hierarchy.dart'
 
 import 'package:kernel/core_types.dart' show CoreTypes;
 
-import 'package:kernel/type_environment.dart' show TypeEnvironment;
-
 import '../../api_prototype/file_system.dart';
 
 import '../../base/instrumentation.dart'
@@ -801,16 +799,9 @@ class SourceLoader<L> extends Loader<L> {
   }
 
   void handleAmbiguousSupertypes(Class cls, Supertype a, Supertype b) {
-    String name = cls.name;
-    TypeEnvironment env = new TypeEnvironment(coreTypes, hierarchy,
-        strongMode: target.strongMode);
-
-    if (cls.isAnonymousMixin) return;
-
-    if (env.isSubtypeOf(a.asInterfaceType, b.asInterfaceType)) return;
     addProblem(
         templateAmbiguousSupertypes.withArguments(
-            name, a.asInterfaceType, b.asInterfaceType),
+            cls.name, a.asInterfaceType, b.asInterfaceType),
         cls.fileOffset,
         noLength,
         cls.fileUri);

pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart

@@ -1932,26 +1932,38 @@ class StrongModeMixinInferrer implements MixinInferrer {
     if (mixinSupertype.typeArguments.isEmpty) {
       // The supertype constraint isn't generic; it doesn't constrain anything.
     } else if (mixinSupertype.classNode.isAnonymousMixin) {
-      // We had a mixin M<X0, ..., Xn> with a superclass constraint of the form
-      // S0 with M0 where S0 and M0 each possibly have type arguments.  That has
-      // been compiled a named mixin application class of the form
+      // We have either a mixin declaration `mixin M<X0, ..., Xn> on S0, S1` or
+      // a VM-style super mixin `abstract class M<X0, ..., Xn> extends S0 with
+      // S1` where S0 and S1 are superclass constraints that possibly have type
+      // arguments.
       //
-      // class S0&M0<...> = S0 with M0;
-      // class M<X0, ..., Xn> extends S0&M0<...>
+      // It has been compiled by naming the superclass to either:
       //
-      // where the type parameters of S0&M0 are the X0, ..., Xn that occured
-      // free in S0 and M0.  Treat S0 and M0 as separate supertype constraints
-      // by recursively calling this algorithm.
+      // abstract class S0&S1<...> extends Object implements S0, S1 {}
+      // abstract class M<X0, ..., Xn> extends S0&S1<...> ...
       //
-      // In some back ends (e.g., the Dart VM) the mixin application classes
-      // themselves are all eliminated by translating them to normal classes.
-      // In that case, the mixin appears as the only interface in the
-      // introduced class:
+      // for a mixin declaration, or else:
       //
-      // class S0&M0<...> extends S0 implements M0 {}
+      // abstract class S0&S1<...> = S0 with S1;
+      // abstract class M<X0, ..., Xn> extends S0&S1<...>
+      //
+      // for a VM-style super mixin.  The type parameters of S0&S1 are the X0,
+      // ..., Xn that occured free in S0 and S1.  Treat S0 and S1 as separate
+      // supertype constraints by recursively calling this algorithm.
+      //
+      // In the Dart VM the mixin application classes themselves are all
+      // eliminated by translating them to normal classes.  In that case, the
+      // mixin appears as the only interface in the introduced class.  We
+      // support three forms for the superclass constraints:
+      //
+      // abstract class S0&S1<...> extends Object implements S0, S1 {}
+      // abstract class S0&S1<...> = S0 with S1;
+      // abstract class S0&S1<...> extends S0 implements S1 {}
       var mixinSuperclass = mixinSupertype.classNode;
       if (mixinSuperclass.mixedInType == null &&
-          mixinSuperclass.implementedTypes.length != 1) {
+          mixinSuperclass.implementedTypes.length != 1 &&
+          (mixinSuperclass.superclass != coreTypes.objectClass ||
+              mixinSuperclass.implementedTypes.length != 2)) {
         unexpected(
             'Compiler-generated mixin applications have a mixin or else '
             'implement exactly one type',
@@ -1961,11 +1973,21 @@ class StrongModeMixinInferrer implements MixinInferrer {
             mixinSuperclass.fileUri);
       }
       var substitution = Substitution.fromSupertype(mixinSupertype);
-      var s0 = substitution.substituteSupertype(mixinSuperclass.supertype);
-      var m0 = substitution.substituteSupertype(mixinSuperclass.mixedInType ??
-          mixinSuperclass.implementedTypes.first);
+      Supertype s0, s1;
+      if (mixinSuperclass.implementedTypes.length == 2) {
+        s0 = mixinSuperclass.implementedTypes[0];
+        s1 = mixinSuperclass.implementedTypes[1];
+      } else if (mixinSuperclass.implementedTypes.length == 1) {
+        s0 = mixinSuperclass.supertype;
+        s1 = mixinSuperclass.implementedTypes.first;
+      } else {
+        s0 = mixinSuperclass.supertype;
+        s1 = mixinSuperclass.mixedInType;
+      }
+      s0 = substitution.substituteSupertype(s0);
+      s1 = substitution.substituteSupertype(s1);
       generateConstraints(hierarchy, mixinClass, baseType, s0);
-      generateConstraints(hierarchy, mixinClass, baseType, m0);
+      generateConstraints(hierarchy, mixinClass, baseType, s1);
     } else {
       // Find the type U0 which is baseType as an instance of mixinSupertype's
       // class.
@@ -2028,11 +2050,10 @@ class StrongModeMixinInferrer implements MixinInferrer {
           return p;
         }
         assert(constraint == null || constraint.upper == constraint.lower);
+        bool exact =
+            constraint != null && constraint.upper != const UnknownType();
         return new TypeParameter(
-            p.name,
-            constraint == null || constraint.upper == const UnknownType()
-                ? p.bound
-                : constraint.upper);
+            p.name, exact ? constraint.upper : p.bound, p.defaultType);
       }).toList();
       // Bounds might mention the mixin class's type parameters so we have to
       // substitute them before calling instantiate to bounds.

pkg/front_end/testcases/incremental_initialize_from_dill/strongmode_mixins_2.yaml

@@ -12,13 +12,13 @@ invalidate:
 sources:
   a.dart: |
     import 'b.dart';
-    class A extends Object with B<C>, D<Object> {}
+    class A extends Object with B<C>, D {}
   b.dart: |
-    abstract class B<ChildType extends Object> extends Object {
+    mixin B<ChildType extends Object> {
       ChildType get child => null;
       set child(ChildType value) {}
     }
 
-    class C extends Object {}
+    class C {}
 
-    abstract class D<T extends Object> extends Object with B<T> {}
+    mixin D<T extends Object> on B<T> {}

pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_1.dart.direct.expect

@@ -1,3 +1,23 @@
+// Formatted problems:
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_1.dart:12:9: Error: '_A&M1&M0' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//         ^
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_1.dart:12:7: Error: 'A' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//       ^
+
+// Unhandled errors:
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_1.dart:12:9: Error: '_A&M1&M0' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//         ^
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_1.dart:12:7: Error: 'A' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//       ^
+
 library;
 import self as self;
 import "dart:core" as core;

pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_1.dart.direct.transformed.expect

@@ -1,3 +1,13 @@
+// Unhandled errors:
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_1.dart:12:9: Error: '_A&M1&M0' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//         ^
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_1.dart:12:7: Error: 'A' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//       ^
+
 library;
 import self as self;
 import "dart:core" as core;

pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_1.dart.outline.expect

@@ -1,3 +1,13 @@
+// Formatted problems:
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_1.dart:12:9: Error: '_A&M1&M0' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//         ^
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_1.dart:12:7: Error: 'A' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//       ^
+
 library;
 import self as self;
 import "dart:core" as core;

pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_2.dart.direct.expect

@@ -1,3 +1,23 @@
+// Formatted problems:
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_2.dart:12:9: Error: '_A&M1&M0' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//         ^
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_2.dart:12:7: Error: 'A' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//       ^
+
+// Unhandled errors:
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_2.dart:12:9: Error: '_A&M1&M0' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//         ^
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_2.dart:12:7: Error: 'A' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//       ^
+
 library;
 import self as self;
 import "dart:core" as core;

pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_2.dart.direct.transformed.expect

@@ -1,3 +1,13 @@
+// Unhandled errors:
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_2.dart:12:9: Error: '_A&M1&M0' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//         ^
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_2.dart:12:7: Error: 'A' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//       ^
+
 library;
 import self as self;
 import "dart:core" as core;

pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_2.dart.outline.expect

@@ -1,3 +1,13 @@
+// Formatted problems:
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_2.dart:12:9: Error: '_A&M1&M0' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//         ^
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_2.dart:12:7: Error: 'A' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//       ^
+
 library;
 import self as self;
 import "dart:core" as core;

pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_3.dart.direct.expect

@@ -1,3 +1,23 @@
+// Formatted problems:
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_3.dart:13:9: Error: '_A&M1&M0' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//         ^
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_3.dart:13:7: Error: 'A' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//       ^
+
+// Unhandled errors:
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_3.dart:13:9: Error: '_A&M1&M0' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//         ^
+//
+// pkg/front_end/testcases/inference/mixin_inference_instantiate_to_bounds_3.dart:13:7: Error: 'A' can't implement both '#lib1::I<dart.core::int>' and '#lib1::I<dynamic>'
+// class A extends M1 with M0 {}
+//       ^
+
 library;
 import self as self;
 import "dart:core" as core;