From 327bc451f8397f393808454ff65ee09bc2cb18ed Mon Sep 17 00:00:00 2001
From: Kallen Tu <kallentu@google.com>
Date: Thu, 26 Sep 2019 18:11:10 +0000
Subject: [PATCH] Added variance support in listeners to ast.

Pass variance data to field in TypeParameter through the listeners.
ast_to_text will print variances for classes and mixins if specified.

Avoids serialization/deserialization (impl in future CL).

Change-Id: I298537604823710f0d30001f4cb5f1e81530959f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/118464
Commit-Queue: Kallen Tu <kallentu@google.com>
Reviewed-by: Dmitry Stefantsov <dmitryas@google.com>
---
 pkg/analyzer/lib/src/fasta/ast_builder.dart   |  3 +-
 .../test/generated/parser_fasta_listener.dart |  5 +-
 .../lib/src/fasta/kernel/body_builder.dart    |  6 +-
 .../src/fasta/parser/forwarding_listener.dart |  5 +-
 .../lib/src/fasta/parser/listener.dart        |  3 +-
 .../lib/src/fasta/parser/type_info_impl.dart  |  4 +-
 .../lib/src/fasta/source/diet_listener.dart   |  3 +-
 .../lib/src/fasta/source/outline_builder.dart |  8 ++-
 .../type_promotion_look_ahead_listener.dart   |  8 ++-
 .../test/fasta/parser/type_info_test.dart     | 67 ++++++++++---------
 pkg/front_end/test/parser_test_listener.dart  |  9 ++-
 .../testcases/text_serialization.status       |  2 +
 .../class_type_parameter_modifier.dart        |  9 +++
 ...ype_parameter_modifier.dart.outline.expect | 10 +++
 ...type_parameter_modifier.dart.strong.expect | 12 ++++
 ...er_modifier.dart.strong.transformed.expect | 12 ++++
 .../mixin_type_parameter_modifier.dart        |  9 +++
 ...ype_parameter_modifier.dart.outline.expect | 12 ++++
 ...type_parameter_modifier.dart.strong.expect | 12 ++++
 ...er_modifier.dart.strong.transformed.expect | 12 ++++
 pkg/front_end/testcases/variance/test.options |  1 +
 pkg/kernel/lib/ast.dart                       | 12 ++++
 22 files changed, 176 insertions(+), 48 deletions(-)
 create mode 100644 pkg/front_end/testcases/variance/class_type_parameter_modifier.dart
 create mode 100644 pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.outline.expect
 create mode 100644 pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.strong.expect
 create mode 100644 pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.strong.transformed.expect
 create mode 100644 pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart
 create mode 100644 pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.outline.expect
 create mode 100644 pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.strong.expect
 create mode 100644 pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.strong.transformed.expect
 create mode 100644 pkg/front_end/testcases/variance/test.options

diff --git a/pkg/analyzer/lib/src/fasta/ast_builder.dart b/pkg/analyzer/lib/src/fasta/ast_builder.dart
index 078a9da4e91..df889e02256 100644
--- a/pkg/analyzer/lib/src/fasta/ast_builder.dart
+++ b/pkg/analyzer/lib/src/fasta/ast_builder.dart
@@ -2090,7 +2090,8 @@ class AstBuilder extends StackListener {
   }
 
   @override
-  void endTypeVariable(Token token, int index, Token extendsOrSuper) {
+  void endTypeVariable(
+      Token token, int index, Token extendsOrSuper, Token variance) {
     debugEvent("TypeVariable");
     assert(extendsOrSuper == null ||
         optional('extends', extendsOrSuper) ||
diff --git a/pkg/analyzer/test/generated/parser_fasta_listener.dart b/pkg/analyzer/test/generated/parser_fasta_listener.dart
index f3145f8ae58..203d6db4f10 100644
--- a/pkg/analyzer/test/generated/parser_fasta_listener.dart
+++ b/pkg/analyzer/test/generated/parser_fasta_listener.dart
@@ -1152,9 +1152,10 @@ class ForwardingTestListener extends ForwardingListener {
   }
 
   @override
-  void endTypeVariable(Token token, int index, Token extendsOrSuper) {
+  void endTypeVariable(
+      Token token, int index, Token extendsOrSuper, Token variance) {
     end('TypeVariable');
-    super.endTypeVariable(token, index, extendsOrSuper);
+    super.endTypeVariable(token, index, extendsOrSuper, variance);
   }
 
   @override
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index dd4884bc232..656b1ae6d1a 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -4767,7 +4767,8 @@ class BodyBuilder extends ScopeListener<JumpTarget>
   }
 
   @override
-  void endTypeVariable(Token token, int index, Token extendsOrSuper) {
+  void endTypeVariable(
+      Token token, int index, Token extendsOrSuper, Token variance) {
     debugEvent("TypeVariable");
     UnresolvedType bound = pop();
     // Peek to leave type parameters on top of stack.
@@ -4775,6 +4776,9 @@ class BodyBuilder extends ScopeListener<JumpTarget>
 
     TypeVariableBuilder variable = typeVariables[index];
     variable.bound = bound?.builder;
+    if (variance != null) {
+      variable.variance = Variance.fromString(variance.lexeme);
+    }
   }
 
   @override
diff --git a/pkg/front_end/lib/src/fasta/parser/forwarding_listener.dart b/pkg/front_end/lib/src/fasta/parser/forwarding_listener.dart
index af3ed3bddb8..f5e93205813 100644
--- a/pkg/front_end/lib/src/fasta/parser/forwarding_listener.dart
+++ b/pkg/front_end/lib/src/fasta/parser/forwarding_listener.dart
@@ -993,8 +993,9 @@ class ForwardingListener implements Listener {
   }
 
   @override
-  void endTypeVariable(Token token, int index, Token extendsOrSuper) {
-    listener?.endTypeVariable(token, index, extendsOrSuper);
+  void endTypeVariable(
+      Token token, int index, Token extendsOrSuper, Token variance) {
+    listener?.endTypeVariable(token, index, extendsOrSuper, variance);
   }
 
   @override
diff --git a/pkg/front_end/lib/src/fasta/parser/listener.dart b/pkg/front_end/lib/src/fasta/parser/listener.dart
index 9c67ac48988..e5f5fad0a93 100644
--- a/pkg/front_end/lib/src/fasta/parser/listener.dart
+++ b/pkg/front_end/lib/src/fasta/parser/listener.dart
@@ -1220,7 +1220,8 @@ class Listener implements UnescapeErrorListener {
   /// - Type bound
   ///
   /// See [beginTypeVariable] for additional substructures.
-  void endTypeVariable(Token token, int index, Token extendsOrSuper) {
+  void endTypeVariable(
+      Token token, int index, Token extendsOrSuper, Token variance) {
     logEvent("TypeVariable");
   }
 
diff --git a/pkg/front_end/lib/src/fasta/parser/type_info_impl.dart b/pkg/front_end/lib/src/fasta/parser/type_info_impl.dart
index 2a16412ec05..de9c32dd3c5 100644
--- a/pkg/front_end/lib/src/fasta/parser/type_info_impl.dart
+++ b/pkg/front_end/lib/src/fasta/parser/type_info_impl.dart
@@ -763,7 +763,7 @@ class SimpleTypeArgument1 extends TypeParamOrArgInfo {
     listener.beginTypeVariable(token);
     listener.handleTypeVariablesDefined(token, 1);
     listener.handleNoType(token);
-    listener.endTypeVariable(endGroup, 0, null);
+    listener.endTypeVariable(endGroup, 0, null, null);
     listener.endTypeVariables(beginGroup, endGroup);
     return endGroup;
   }
@@ -1075,7 +1075,7 @@ class ComplexTypeParamOrArgInfo extends TypeParamOrArgInfo {
       // Type variables are "completed" in reverse order, so capture the last
       // consumed token from the first "completed" type variable.
       token ??= token2;
-      listener.endTypeVariable(next2, --count, extendsOrSuper);
+      listener.endTypeVariable(next2, --count, extendsOrSuper, variance);
 
       typeStarts = typeStarts.tail;
       superTypeInfos = superTypeInfos.tail;
diff --git a/pkg/front_end/lib/src/fasta/source/diet_listener.dart b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
index e24dd3c3e15..10bb91eb352 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
@@ -544,7 +544,8 @@ class DietListener extends StackListener {
   }
 
   @override
-  void endTypeVariable(Token token, int index, Token extendsOrSuper) {
+  void endTypeVariable(
+      Token token, int index, Token extendsOrSuper, Token variance) {
     debugEvent("endTypeVariable");
   }
 
diff --git a/pkg/front_end/lib/src/fasta/source/outline_builder.dart b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
index 77ca872f32f..03775991ea9 100644
--- a/pkg/front_end/lib/src/fasta/source/outline_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
@@ -4,7 +4,7 @@
 
 library fasta.outline_builder;
 
-import 'package:kernel/ast.dart' show ProcedureKind;
+import 'package:kernel/ast.dart' show ProcedureKind, Variance;
 
 import '../builder/builder.dart';
 
@@ -1574,13 +1574,17 @@ class OutlineBuilder extends StackListener {
   }
 
   @override
-  void endTypeVariable(Token token, int index, Token extendsOrSuper) {
+  void endTypeVariable(
+      Token token, int index, Token extendsOrSuper, Token variance) {
     debugEvent("endTypeVariable");
     TypeBuilder bound = nullIfParserRecovery(pop());
     // Peek to leave type parameters on top of stack.
     List<TypeVariableBuilder> typeParameters = peek();
     if (typeParameters != null) {
       typeParameters[index].bound = bound;
+      if (variance != null) {
+        typeParameters[index].variance = Variance.fromString(variance.lexeme);
+      }
     }
   }
 
diff --git a/pkg/front_end/lib/src/fasta/source/type_promotion_look_ahead_listener.dart b/pkg/front_end/lib/src/fasta/source/type_promotion_look_ahead_listener.dart
index 8a1c08d928e..67cdaec9ac9 100644
--- a/pkg/front_end/lib/src/fasta/source/type_promotion_look_ahead_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/type_promotion_look_ahead_listener.dart
@@ -1316,7 +1316,8 @@ class TypePromotionLookAheadListener extends Listener {
   }
 
   @override
-  void endTypeVariable(Token token, int index, Token extendsOrSuper) {
+  void endTypeVariable(
+      Token token, int index, Token extendsOrSuper, Token variance) {
     debugEvent("TypeVariable", token);
     state.pop(); // Name.
   }
@@ -1326,6 +1327,11 @@ class TypePromotionLookAheadListener extends Listener {
     debugEvent("TypeVariables", beginToken);
   }
 
+  @override
+  void handleVarianceModifier(Token variance) {
+    debugEvent("VarianceModifier", variance);
+  }
+
   @override
   void handleNoTypeVariables(Token token) {
     debugEvent("NoTypeVariables", token);
diff --git a/pkg/front_end/test/fasta/parser/type_info_test.dart b/pkg/front_end/test/fasta/parser/type_info_test.dart
index 1dd605140c8..dc5203c2ab0 100644
--- a/pkg/front_end/test/fasta/parser/type_info_test.dart
+++ b/pkg/front_end/test/fasta/parser/type_info_test.dart
@@ -695,7 +695,7 @@ class TypeInfoTest {
       'beginTypeVariable T',
       'handleTypeVariablesDefined T 1',
       'handleNoType T',
-      'endTypeVariable > 0 null',
+      'endTypeVariable > 0 null null',
       'endTypeVariables < >',
       'beginFunctionType Function',
       'handleNoType ',
@@ -729,7 +729,7 @@ class TypeInfoTest {
       'beginTypeVariable T',
       'handleTypeVariablesDefined T 1',
       'handleNoType T',
-      'endTypeVariable > 0 null',
+      'endTypeVariable > 0 null null',
       'endTypeVariables < >',
       'beginFunctionType Function',
       'handleNoType ',
@@ -1377,7 +1377,7 @@ class TypeInfoTest {
           'beginTypeVariable T',
           'handleTypeVariablesDefined T 1',
           'handleNoType T',
-          'endTypeVariable > 0 null',
+          'endTypeVariable > 0 null null',
           'endTypeVariables < >',
           'beginFunctionType C',
           'beginTypeVariables <',
@@ -1387,7 +1387,7 @@ class TypeInfoTest {
           'beginTypeVariable T',
           'handleTypeVariablesDefined T 1',
           'handleNoType T',
-          'endTypeVariable > 0 null',
+          'endTypeVariable > 0 null null',
           'endTypeVariables < >',
           'beginFunctionType C',
           'handleIdentifier C prefixedTypeReference',
@@ -1638,7 +1638,7 @@ class SimpleTypeParamOrArgTest {
       'beginTypeVariable T',
       'handleTypeVariablesDefined T 1',
       'handleNoType T',
-      'endTypeVariable > 0 null',
+      'endTypeVariable > 0 null null',
       'endTypeVariables < >',
     ]);
     expect(listener.errors, isNull);
@@ -2023,9 +2023,9 @@ class TypeParamOrArgInfoTest {
       'beginTypeVariable T',
       'handleTypeVariablesDefined T 2',
       'handleNoType T',
-      'endTypeVariable > 1 null',
+      'endTypeVariable > 1 null null',
       'handleNoType S',
-      'endTypeVariable , 0 null',
+      'endTypeVariable , 0 null null',
       'endTypeVariables < >',
     ]);
     expectComplexTypeParam('<S extends T>',
@@ -2040,7 +2040,7 @@ class TypeParamOrArgInfoTest {
           'handleIdentifier T typeReference',
           'handleNoTypeArguments >',
           'handleType T null',
-          'endTypeVariable > 0 extends',
+          'endTypeVariable > 0 extends null',
           'endTypeVariables < >',
         ]);
     expectComplexTypeParam('<S extends List<T>>',
@@ -2059,7 +2059,7 @@ class TypeParamOrArgInfoTest {
           'handleType T null',
           'endTypeArguments 1 < >',
           'handleType List null',
-          'endTypeVariable > 0 extends',
+          'endTypeVariable > 0 extends null',
           'endTypeVariables < >',
         ]);
     expectComplexTypeParam('<R, S extends void Function()>',
@@ -2081,9 +2081,9 @@ class TypeParamOrArgInfoTest {
           'beginFormalParameters ( MemberKind.GeneralizedFunctionType',
           'endFormalParameters 0 ( ) MemberKind.GeneralizedFunctionType',
           'endFunctionType Function null',
-          'endTypeVariable > 1 extends',
+          'endTypeVariable > 1 extends null',
           'handleNoType R',
-          'endTypeVariable , 0 null',
+          'endTypeVariable , 0 null null',
           'endTypeVariables < >',
         ]);
     expectComplexTypeParam('<@A S,T>', typeArgumentCount: 2, expectedCalls: [
@@ -2103,9 +2103,9 @@ class TypeParamOrArgInfoTest {
       'beginTypeVariable T',
       'handleTypeVariablesDefined T 2',
       'handleNoType T',
-      'endTypeVariable > 1 null',
+      'endTypeVariable > 1 null null',
       'handleNoType S',
-      'endTypeVariable , 0 null',
+      'endTypeVariable , 0 null null',
       'endTypeVariables < >',
     ]);
     expectComplexTypeParam('<@A() S,T>', typeArgumentCount: 2, expectedCalls: [
@@ -2126,9 +2126,9 @@ class TypeParamOrArgInfoTest {
       'beginTypeVariable T',
       'handleTypeVariablesDefined T 2',
       'handleNoType T',
-      'endTypeVariable > 1 null',
+      'endTypeVariable > 1 null null',
       'handleNoType S',
-      'endTypeVariable , 0 null',
+      'endTypeVariable , 0 null null',
       'endTypeVariables < >',
     ]);
     expectComplexTypeParam('<@A() @B S,T>',
@@ -2156,9 +2156,9 @@ class TypeParamOrArgInfoTest {
           'beginTypeVariable T',
           'handleTypeVariablesDefined T 2',
           'handleNoType T',
-          'endTypeVariable > 1 null',
+          'endTypeVariable > 1 null null',
           'handleNoType S',
-          'endTypeVariable , 0 null',
+          'endTypeVariable , 0 null null',
           'endTypeVariables < >',
         ]);
   }
@@ -2179,7 +2179,7 @@ class TypeParamOrArgInfoTest {
           'handleIdentifier void typeReference',
           'handleNoTypeArguments >',
           'handleType void null',
-          'endTypeVariable > 0 extends',
+          'endTypeVariable > 0 extends null',
           'endTypeVariables < >'
         ]);
   }
@@ -2198,7 +2198,7 @@ class TypeParamOrArgInfoTest {
           'beginTypeVariable S',
           'handleTypeVariablesDefined S 1',
           'handleNoType S',
-          'endTypeVariable Function 0 null',
+          'endTypeVariable Function 0 null null',
           'endTypeVariables < >',
         ]);
     expectComplexTypeParam('<void Function()>',
@@ -2214,7 +2214,7 @@ class TypeParamOrArgInfoTest {
           'beginTypeVariable ',
           'handleTypeVariablesDefined  1',
           'handleNoType ',
-          'endTypeVariable void 0 null',
+          'endTypeVariable void 0 null null',
           'endTypeVariables < >',
         ]);
     expectComplexTypeParam('<S<T>>', typeArgumentCount: 1, expectedErrors: [
@@ -2227,7 +2227,7 @@ class TypeParamOrArgInfoTest {
       'beginTypeVariable S',
       'handleTypeVariablesDefined S 1',
       'handleNoType S',
-      'endTypeVariable < 0 null',
+      'endTypeVariable < 0 null null',
       'endTypeVariables < >',
     ]);
     expectComplexTypeParam('<S T>',
@@ -2270,7 +2270,7 @@ class TypeParamOrArgInfoTest {
           'handleType T null',
           'endTypeArguments 1 < >',
           'handleType List null',
-          'endTypeVariable fieldName 0 extends',
+          'endTypeVariable fieldName 0 extends null',
           'endTypeVariables < >',
         ]);
   }
@@ -2292,7 +2292,7 @@ class TypeParamOrArgInfoTest {
           'handleType T null',
           'endTypeArguments 1 < >',
           'handleType Comparable null',
-          'endTypeVariable > 0 extends',
+          'endTypeVariable > 0 extends null',
           'endTypeVariables < >',
         ]);
     expectComplexTypeParam('<T extends Comparable<S>, S>',
@@ -2309,7 +2309,7 @@ class TypeParamOrArgInfoTest {
           'beginTypeVariable S',
           'handleTypeVariablesDefined S 2',
           'handleNoType S',
-          'endTypeVariable > 1 null',
+          'endTypeVariable > 1 null null',
           'handleIdentifier Comparable typeReference',
           'beginTypeArguments <',
           'handleIdentifier S typeReference',
@@ -2317,7 +2317,7 @@ class TypeParamOrArgInfoTest {
           'handleType S null',
           'endTypeArguments 1 < >',
           'handleType Comparable null',
-          'endTypeVariable , 0 extends',
+          'endTypeVariable , 0 extends null',
           'endTypeVariables < >'
         ]);
     expectComplexTypeParam('<T extends Function(T)>',
@@ -2345,7 +2345,7 @@ class TypeParamOrArgInfoTest {
               'MemberKind.GeneralizedFunctionType',
           'endFormalParameters 1 ( ) MemberKind.GeneralizedFunctionType',
           'endFunctionType Function null',
-          'endTypeVariable > 0 extends',
+          'endTypeVariable > 0 extends null',
           'endTypeVariables < >'
         ]);
     expectComplexTypeParam('<T extends List<List<T>>>',
@@ -2368,7 +2368,7 @@ class TypeParamOrArgInfoTest {
           'handleType List null',
           'endTypeArguments 1 < >',
           'handleType List null',
-          'endTypeVariable > 0 extends',
+          'endTypeVariable > 0 extends null',
           'endTypeVariables < >'
         ]);
     expectComplexTypeParam('<T extends List<Map<S, T>>>',
@@ -2394,7 +2394,7 @@ class TypeParamOrArgInfoTest {
           'handleType Map null',
           'endTypeArguments 1 < >',
           'handleType List null',
-          'endTypeVariable > 0 extends',
+          'endTypeVariable > 0 extends null',
           'endTypeVariables < >'
         ]);
     expectComplexTypeParam('<T extends List<Map<S, T>>>=',
@@ -2421,7 +2421,7 @@ class TypeParamOrArgInfoTest {
           'handleType Map null',
           'endTypeArguments 1 < >',
           'handleType List null',
-          'endTypeVariable >= 0 extends',
+          'endTypeVariable >= 0 extends null',
           'endTypeVariables < >'
         ]);
   }
@@ -2441,7 +2441,7 @@ class TypeParamOrArgInfoTest {
           'beginTypeVariable S',
           'handleTypeVariablesDefined S 1',
           'handleNoType S',
-          'endTypeVariable < 0 null',
+          'endTypeVariable < 0 null null',
           'endTypeVariables < >',
         ]);
     expectComplexTypeParam('<S();> A',
@@ -2459,7 +2459,7 @@ class TypeParamOrArgInfoTest {
           'beginTypeVariable S',
           'handleTypeVariablesDefined S 1',
           'handleNoType S',
-          'endTypeVariable ( 0 null',
+          'endTypeVariable ( 0 null null',
           'endTypeVariables < >',
         ]);
   }
@@ -2842,8 +2842,9 @@ class TypeInfoListener implements Listener {
   }
 
   @override
-  void endTypeVariable(Token token, int index, Token extendsOrSuper) {
-    calls.add('endTypeVariable $token $index $extendsOrSuper');
+  void endTypeVariable(
+      Token token, int index, Token extendsOrSuper, Token variance) {
+    calls.add('endTypeVariable $token $index $extendsOrSuper $variance');
     assertTokenInStream(token);
     assertTokenInStream(extendsOrSuper);
   }
diff --git a/pkg/front_end/test/parser_test_listener.dart b/pkg/front_end/test/parser_test_listener.dart
index 2877ed29bbd..8bd1eadfb91 100644
--- a/pkg/front_end/test/parser_test_listener.dart
+++ b/pkg/front_end/test/parser_test_listener.dart
@@ -1204,9 +1204,14 @@ class ParserTestListener implements Listener {
     doPrint('handleTypeVariablesDefined(' '$token, ' '$count)');
   }
 
-  void endTypeVariable(Token token, int index, Token extendsOrSuper) {
+  void endTypeVariable(
+      Token token, int index, Token extendsOrSuper, Token variance) {
     indent--;
-    doPrint('endTypeVariable(' '$token, ' '$index, ' '$extendsOrSuper)');
+    doPrint('endTypeVariable('
+        '$token, '
+        '$index, '
+        '$extendsOrSuper, '
+        '$variance)');
   }
 
   void beginTypeVariables(Token token) {
diff --git a/pkg/front_end/testcases/text_serialization.status b/pkg/front_end/testcases/text_serialization.status
index da0cb3de945..6bafcf8a4e2 100644
--- a/pkg/front_end/testcases/text_serialization.status
+++ b/pkg/front_end/testcases/text_serialization.status
@@ -1118,4 +1118,6 @@ runtime_checks_new/stub_from_interface_covariantInterface_from_class: TextSerial
 runtime_checks_new/stub_from_interface_covariant_from_interface: TextSerializationFailure # Was: Pass
 runtime_checks_new/stub_from_interface_covariant_from_super: TextSerializationFailure # Was: Pass
 set_literals/disambiguation_rule: TextSerializationFailure # Was: RuntimeError
+variance/class_type_parameter_modifier: TextSerializationFailure
+variance/mixin_type_parameter_modifier: TextSerializationFailure
 top_level_variance_test: TextSerializationFailure
diff --git a/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart b/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart
new file mode 100644
index 00000000000..71aa5cf6b90
--- /dev/null
+++ b/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart
@@ -0,0 +1,9 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+class A<out X, in Y, inout Z> {}
+
+main() {
+  A a = new A();
+}
diff --git a/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.outline.expect b/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.outline.expect
new file mode 100644
index 00000000000..05b61d880a7
--- /dev/null
+++ b/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.outline.expect
@@ -0,0 +1,10 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class A<X extends core::Object* = dynamic, contravariant Y extends core::Object* = dynamic, invariant Z extends core::Object* = dynamic> extends core::Object {
+  synthetic constructor •() → self::A<self::A::X*, self::A::Y*, self::A::Z*>*
+    ;
+}
+static method main() → dynamic
+  ;
diff --git a/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.strong.expect b/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.strong.expect
new file mode 100644
index 00000000000..cb21b6a71d4
--- /dev/null
+++ b/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.strong.expect
@@ -0,0 +1,12 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class A<X extends core::Object* = dynamic, contravariant Y extends core::Object* = dynamic, invariant Z extends core::Object* = dynamic> extends core::Object {
+  synthetic constructor •() → self::A<self::A::X*, self::A::Y*, self::A::Z*>*
+    : super core::Object::•()
+    ;
+}
+static method main() → dynamic {
+  self::A<dynamic, dynamic, dynamic>* a = new self::A::•<dynamic, dynamic, dynamic>();
+}
diff --git a/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.strong.transformed.expect b/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.strong.transformed.expect
new file mode 100644
index 00000000000..cb21b6a71d4
--- /dev/null
+++ b/pkg/front_end/testcases/variance/class_type_parameter_modifier.dart.strong.transformed.expect
@@ -0,0 +1,12 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class A<X extends core::Object* = dynamic, contravariant Y extends core::Object* = dynamic, invariant Z extends core::Object* = dynamic> extends core::Object {
+  synthetic constructor •() → self::A<self::A::X*, self::A::Y*, self::A::Z*>*
+    : super core::Object::•()
+    ;
+}
+static method main() → dynamic {
+  self::A<dynamic, dynamic, dynamic>* a = new self::A::•<dynamic, dynamic, dynamic>();
+}
diff --git a/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart b/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart
new file mode 100644
index 00000000000..2aefefba907
--- /dev/null
+++ b/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart
@@ -0,0 +1,9 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+class A {}
+
+mixin B<inout X, out Y, in Z> on A {}
+
+main() {}
diff --git a/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.outline.expect b/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.outline.expect
new file mode 100644
index 00000000000..44fe61abe9f
--- /dev/null
+++ b/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.outline.expect
@@ -0,0 +1,12 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class A extends core::Object {
+  synthetic constructor •() → self::A*
+    ;
+}
+abstract class B<invariant X extends core::Object* = dynamic, Y extends core::Object* = dynamic, contravariant Z extends core::Object* = dynamic> extends self::A {
+}
+static method main() → dynamic
+  ;
diff --git a/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.strong.expect b/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.strong.expect
new file mode 100644
index 00000000000..0c6c3cdf00a
--- /dev/null
+++ b/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.strong.expect
@@ -0,0 +1,12 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class A extends core::Object {
+  synthetic constructor •() → self::A*
+    : super core::Object::•()
+    ;
+}
+abstract class B<invariant X extends core::Object* = dynamic, Y extends core::Object* = dynamic, contravariant Z extends core::Object* = dynamic> extends self::A {
+}
+static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.strong.transformed.expect b/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.strong.transformed.expect
new file mode 100644
index 00000000000..0c6c3cdf00a
--- /dev/null
+++ b/pkg/front_end/testcases/variance/mixin_type_parameter_modifier.dart.strong.transformed.expect
@@ -0,0 +1,12 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class A extends core::Object {
+  synthetic constructor •() → self::A*
+    : super core::Object::•()
+    ;
+}
+abstract class B<invariant X extends core::Object* = dynamic, Y extends core::Object* = dynamic, contravariant Z extends core::Object* = dynamic> extends self::A {
+}
+static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/variance/test.options b/pkg/front_end/testcases/variance/test.options
new file mode 100644
index 00000000000..3ce5008900a
--- /dev/null
+++ b/pkg/front_end/testcases/variance/test.options
@@ -0,0 +1 @@
+--enable-experiment=variance
diff --git a/pkg/kernel/lib/ast.dart b/pkg/kernel/lib/ast.dart
index 1f1835c1258..cd777e3a370 100644
--- a/pkg/kernel/lib/ast.dart
+++ b/pkg/kernel/lib/ast.dart
@@ -6003,6 +6003,18 @@ class Variance {
     if (a == invariant || b == invariant) return invariant;
     return a == b ? covariant : contravariant;
   }
+
+  static int fromString(String variance) {
+    if (variance == "in") {
+      return contravariant;
+    } else if (variance == "inout") {
+      return invariant;
+    } else if (variance == "out") {
+      return covariant;
+    } else {
+      return unrelated;
+    }
+  }
 }
 
 /// Declaration of a type variable.