Implement 'covariant' modifier for dart2js.

Also adds some tests.

Fixes #28165

BUG= http://dartbug.com/28165
R=sigmund@google.com

Review-Url: https://codereview.chromium.org/2626843003 .

pkg/compiler/lib/src/parser/parser.dart

@@ -426,6 +426,15 @@ class Parser {
   Token parseFormalParameter(Token token, FormalParameterType type) {
     token = parseMetadataStar(token, forParameter: true);
     listener.beginFormalParameter(token);
+
+    // Skip over `covariant` token, if the next token is an identifier or
+    // modifier.
+    // This enables the case where `covariant` is the name of the parameter:
+    //    void foo(covariant);
+    if (identical(token.stringValue, 'covariant') &&
+        token.next.isIdentifier() || isModifier(token.next)) {
+      token = token.next;
+    }
     token = parseModifiers(token);
     // TODO(ahe): Validate that there are formal parameters if void.
     token = parseReturnTypeOpt(token);
@@ -988,9 +997,29 @@ class Parser {
     return null;
   }
 
+  /// Removes the optional `covariant` token from the modifiers, if there
+  /// is no `static` in the list, and `covariant` is the first modifier.
+  Link<Token> removeOptCovariantTokenIfNotStatic(Link<Token> modifiers) {
+    if (modifiers.isEmpty ||
+        !identical(modifiers.first.stringValue, 'covariant')) {
+      return modifiers;
+    }
+    for (Token modifier in modifiers.tail) {
+      if (identical(modifier.stringValue, 'static')) {
+        return modifiers;
+      }
+    }
+    return modifiers.tail;
+  }
+
   Token parseFields(Token start, Link<Token> modifiers, Token type,
       Token getOrSet, Token name, bool isTopLevel) {
     bool hasType = type != null;
+
+    if (getOrSet == null && !isTopLevel) {
+      modifiers = removeOptCovariantTokenIfNotStatic(modifiers);
+    }
+
     Token varFinalOrConst =
         expectVarFinalOrConst(modifiers, hasType, !isTopLevel);
     bool isVar = false;

pkg/compiler/lib/src/tokens/keyword.dart

@@ -53,6 +53,7 @@ class Keyword {
 
     const Keyword("abstract", isBuiltIn: true),
     const Keyword("as", info: Precedence.AS_INFO, isBuiltIn: true),
+    const Keyword("covariant", isBuiltIn: true),
     const Keyword("dynamic", isBuiltIn: true),
     const Keyword("export", isBuiltIn: true),
     const Keyword("external", isBuiltIn: true),
@@ -77,7 +78,7 @@ class Keyword {
     const Keyword("async", isPseudo: true),
     const Keyword("sync", isPseudo: true),
     const Keyword("await", isPseudo: true),
-    const Keyword("yield", isPseudo: true)
+    const Keyword("yield", isPseudo: true),
   ];
 
   final String syntax;

tests/language/covariant_override_test.dart

@@ -0,0 +1,92 @@
+
+// Copyright (c) 2017, 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.
+
+library covariant_override_test;
+
+// This test contains cases where `covariant` is used as intended.
+
+abstract class A {
+  A(this.f1, this.f2, this.f3);
+
+  // Normal usage, "by design": superclass requests covariance.
+  void m1(covariant Object o);
+
+  // Normal usage, "ad hoc": subclass requests covariance.
+  void m2(Object o);
+
+  // Syntactic special case: omit the type in subclass.
+  void m3(Object o);
+
+  // Positional optional arguments.
+  void m4([covariant Object o]);
+  void m5([Object o]);
+  void m6([Object o]);
+
+  // Named arguments.
+  void m7({covariant Object arg});
+  void m8({Object arg});
+  void m9({Object arg});
+
+  // Normal usage on field, "by design": superclass requests covariance.
+  covariant Object f1;
+
+  // Normal usage on field, "ad hoc": subclass requests covariance.
+  Object f2;
+
+  // Syntactic special case.
+  Object f3;
+}
+
+abstract class B extends A {
+  B(num f1, num f2, num f3): super(f1, f2, f3);
+
+  void m1(num n);
+  void m2(covariant num n);
+  void m3(covariant n);
+  void m4([num n]);
+  void m5([covariant num n]);
+  void m6([covariant n]);
+  void m7({num arg});
+  void m8({covariant num arg});
+  void m9({covariant arg});
+  void set f1(num n);
+  void set f2(covariant num n);
+  void set f3(covariant n);
+}
+
+class C extends B {
+  C(int f1, int f2, int f3): super(f1, f2, f3);
+  
+  void m1(int i) {}
+  void m2(int i) {}
+  void m3(int i) {}
+  void m4([int i]) {}
+  void m5([int i]) {}
+  void m6([int i]) {}
+  void m7({int arg}) {}
+  void m8({int arg}) {}
+  void m9({int arg}) {}
+  void set f1(int i) {}
+  void set f2(int i) {}
+  void set f3(int i) {}
+}
+
+main() {
+  // For Dart 1.x, `covariant` has no runtime semantics; we just ensure
+  // that the code is not unused, such that we know it will be parsed.
+  A a = new C(39, 40, 41);
+  a.m1(42);
+  a.m2(42);
+  a.m3(42);
+  a.m4(42);
+  a.m5(42);
+  a.m6(42);
+  a.m7(arg: 42);
+  a.m8(arg: 42);
+  a.m9(arg: 42);
+  a.f1 = 42;
+  a.f2 = 42;
+  a.f3 = 42;
+}

tests/language/covariant_test.dart

@@ -0,0 +1,378 @@
+// Copyright (c) 2017, 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.
+
+// Test that `covariant` can be parsed (and ignored) by
+// dart2js and the VM.
+// This test only checks for non-strong mode behavior.
+//
+// Generally, `covariant` should be ignored, when it is used in the right
+// places.
+
+import 'package:expect/expect.dart';
+
+// Top level field may not have a covariant.
+// Would be considered a minor (acceptable) bug, if it was accepted here too.
+covariant  /// 00: compile-time error
+int x0;
+
+// Getters may never have `covariant`. (Neither on the top-level nor as members)
+covariant  /// 01: compile-time error
+int get x1 => 499;
+
+// Top level setters may not have a covariant.
+// Would be considered a minor (acceptable) bug, if it was accepted here too.
+void set x2(
+    covariant /// 02: compile-time error
+    int val) {}
+
+// Same as above, but with `covariant` in different positions.
+// The `covariant` is just wrong there.
+
+int
+covariant  /// 03: compile-time error
+x3;
+
+int
+covariant  /// 04: compile-time error
+get x4 => 499;
+
+void set x5(
+    int
+    covariant /// 05: compile-time error
+    val) {}
+
+
+// Same without types.
+
+// Since `covariant` is a built-in identifier, it is not allowed here.
+covariant x6;  /// 06: compile-time error
+
+// Getters may never have `covariant`.
+covariant  /// 07: compile-time error
+get x7 => 499;
+
+// Top level setters may not have a covariant.
+// Would be considered a minor (acceptable) bug, if it was accepted here too.
+void set x8(
+    covariant /// 08: compile-time error
+    val) {}
+
+// If there is no type, then `covariant` is simply the parameter name:
+void set x9(covariant) {}
+
+// Covariant won't work on return types.
+covariant  /// 10: compile-time error
+int f10() => 499;
+
+// Covariant won't work as a return type.
+covariant  /// 11: compile-time error
+f11() => 499;
+
+// Covariant should not work on top-level methods.
+// It's a minor (acceptable) bug to not error out here.
+int f12(
+    covariant /// 12: compile-time error
+    int x) => 499;
+
+// `Covariant` must be in front of the types.
+int f13(
+    int
+    covariant /// 13: compile-time error
+    x) => 499;
+
+// Covariant should not work on top-level methods.
+// It's a minor (acceptable) bug to not error out here.
+int f14(
+    covariant /// 14: compile-time error
+    final
+    x) => 499;
+
+// `Covariant` must be in front of modifiers.
+int f15(
+    final
+    covariant /// 15: compile-time error
+    x) => 499;
+
+// Covariant should not work on top-level methods.
+// It's a minor (acceptable) bug to not error out here.
+int f16(
+    covariant /// 16: compile-time error
+    final
+    int
+    x) => 499;
+
+// `Covariant` must be in front of modifiers.
+int f17(
+    final
+    covariant /// 17: compile-time error
+    int
+    x) => 499;
+
+// On its own, `covariant` is just a parameter name.
+int f18(covariant) => covariant;
+
+// All of the above as statics in a class.
+class A {
+  // Static fields may not have a covariant.
+  // Would be considered a minor (acceptable) bug, if it was accepted here too.
+  static
+  covariant  /// 20: compile-time error
+  int x20;
+
+  // Getters may never have `covariant`.
+  static
+  covariant  /// 21: compile-time error
+  int get x21 => 499;
+
+  // Getters may never have `covariant`.
+  covariant  /// 21b: compile-time error
+  static
+  int get x21b => 499;
+
+  // Static setters may not have a covariant.
+  // Would be considered a minor (acceptable) bug, if it was accepted here too.
+  static void set x22(
+      covariant /// 22: compile-time error
+      int val) {}
+
+  // Same as above, but with `covariant` in different positions.
+  // The `covariant` is just wrong there.
+
+  static int
+  covariant  /// 23: compile-time error
+  x23;
+
+  static int
+  covariant  /// 24: compile-time error
+  get x24 => 499;
+
+  static void set x25(
+    int
+    covariant /// 25: compile-time error
+    val) {}
+
+  // Since `covariant` is a built-in identifier, it is not allowed here.
+  static covariant x26; /// 26: compile-time error
+
+  // Getters may never have `covariant`.
+  static
+  covariant  /// 27: compile-time error
+  get x27 => 499;
+
+  covariant  /// 27b: compile-time error
+  static
+  get x27b => 499;
+
+  // Static setters may not have a covariant.
+  // Would be considered a minor (acceptable) bug, if it was accepted here too.
+  static void set x28(
+      covariant /// 28: compile-time error
+      val) {}
+
+  // If there is no type, then `covariant` is simply the parameter name:
+  static void set x29(covariant) {}
+
+  // Covariant won't work on return types.
+  static
+  covariant  /// 30: compile-time error
+  int f30() => 499;
+
+  covariant  /// 30b: compile-time error
+  static
+  int f30b() => 499;
+
+  // Covariant won't work as a return type.
+  static
+  covariant  /// 31: compile-time error
+  f31() => 499;
+
+  covariant  /// 31b: compile-time error
+  static
+  f31b() => 499;
+
+  // Covariant should not work on static methods.
+  // It's a minor (acceptable) bug to not error out here.
+  static int f32(
+      covariant /// 32: compile-time error
+      int x) => 499;
+
+  // `Covariant` must be in front of the types.
+  static int f33(
+      int
+      covariant /// 33: compile-time error
+      x) => 499;
+
+  // Covariant should not work on top-level methods.
+  // It's a minor (acceptable) bug to not error out here.
+  static int f34(
+      covariant /// 34: compile-time error
+      final
+      x) => 499;
+
+  // `Covariant` must be in front of modifiers.
+  static int f35(
+      final
+      covariant /// 35: compile-time error
+      x) => 499;
+
+  // Covariant should not work on top-level methods.
+  // It's a minor (acceptable) bug to not error out here.
+  static int f36(
+      covariant /// 36: compile-time error
+      final
+      int
+      x) => 499;
+
+  // `Covariant` must be in front of modifiers.
+  static int f37(
+      final
+      covariant /// 37: compile-time error
+      int
+      x) => 499;
+
+  // `Covariant` on its own is just a parameter name.
+  static int f38(covariant) => covariant;
+}
+
+// All of the above as instance members in a class.
+class B {
+  covariant int x40;
+
+  // Getters may never have `covariant`.
+  covariant  /// 41: compile-time error
+  int get x41 => 499;
+
+  void set x42(covariant int val) {}
+
+  // `covariant` in the wrong position.
+  int
+  covariant  /// 43: compile-time error
+  x43;
+
+  // `covariant` in the wrong position.
+  int
+  covariant  /// 44: compile-time error
+  get x44 => 499;
+
+  void set x45(
+    int
+    covariant /// 45: compile-time error
+    val) {}
+
+  // Since `covariant` is a built-in identifier, it is not allowed here.
+  covariant x46; /// 46: compile-time error
+
+  // Getters may never have `covariant`.
+  covariant  /// 47: compile-time error
+  get x47 => 499;
+
+  void set x48(covariant val) {}
+
+  // If there is no type, then `covariant` is simply the parameter name:
+  void set x49(covariant) {}
+
+  // Covariant won't work on return types.
+  covariant  /// 50: compile-time error
+  int f50() => 499;
+
+  // Covariant won't work as a return type.
+  covariant  /// 51: compile-time error
+  f51() => 499;
+
+  int f52(covariant int x) => 499;
+
+  // `Covariant` must be in front of the types.
+  int f53(
+      int
+      covariant /// 53: compile-time error
+      x) => 499;
+
+  int f54(covariant final x) => 499;
+
+  // `Covariant` must be in front of modifiers.
+  int f55(
+      final
+      covariant /// 55: compile-time error
+      x) => 499;
+
+  int f56(covariant final int x) => 499;
+
+  // `Covariant` must be in front of modifiers.
+  int f57(
+      final
+      covariant /// 57: compile-time error
+      int
+      x) => 499;
+
+  // `Covariant` on its own is just a parameter name.
+  int f58(covariant) => covariant;
+}
+
+void use(x) {}
+
+main() {
+  x0 = 0;
+  use(x1);
+  x2 = 499;
+  use(x3);
+  use(x4);
+  x5 = 42;
+  x6 = 0; /// 06: continued
+  use(x7);
+  x8 = 11;
+  x9 = 12;
+  use(f10());
+  use(f11());
+  use(f12(2));
+  use(f13(3));
+  use(f14(3));
+  use(f15(3));
+  use(f16(3));
+  use(f17(3));
+  Expect.equals(123, f18(123));
+
+  A.x20 = 0;
+  use(A.x21);
+  use(A.x21b);
+  A.x22 = 499;
+  use(A.x23);
+  use(A.x24);
+  A.x25 = 42;
+  A.x26 = 0; /// 26: continued
+  use(A.x27);
+  use(A.x27b);
+  A.x28 = 11;
+  A.x29 = 12;
+  use(A.f30());
+  use(A.f31());
+  use(A.f31b());
+  use(A.f32(2));
+  use(A.f33(3));
+  use(A.f34(3));
+  use(A.f35(3));
+  use(A.f36(3));
+  use(A.f37(3));
+  Expect.equals(1234, A.f38(1234));
+
+  var b = new B();
+  b.x40 = 0;
+  use(b.x41);
+  b.x42 = 499;
+  use(b.x43);
+  use(b.x44);
+  b.x45 = 42;
+  b.x46 = 0; /// 46: continued
+  use(b.x47);
+  b.x48 = 11;
+  b.x49 = 12;
+  use(b.f50());
+  use(b.f51());
+  use(b.f52(2));
+  use(b.f53(2));
+  use(b.f54(3));
+  use(b.f55(3));
+  use(b.f56(3));
+  use(b.f57(3));
+  Expect.equals(12345, b.f58(12345));
+}

tests/language/language.status

@@ -51,6 +51,10 @@ async_star_cancel_while_paused_test: RuntimeError
 # Fails because `as T` is an error rather than being treated like `as dynamic`.
 generic_methods_type_expression_test: RuntimeError # Issue 27460
 
+# Doesn't yet implement `covariant` keyword.
+covariant_test/none: CompileTimeError # Issue 28166
+covariant_override_test: CompileTimeError # Issue 28166
+
 [ ($compiler == none || $compiler == precompiler || $compiler == app_jit) && $checked ]
 # These generic functions tests pass for the wrong reason in checked mode,
 # because the parsed type parameters are mapped to dynamic type.

tests/language/language_analyzer2.status

@@ -7,6 +7,10 @@
 regress_26668_test: Fail # Issue 26678
 regress_27617_test/1: MissingCompileTimeError
 
+# Doesn't yet implement `covariant` keyword.
+covariant_test/none: CompileTimeError # Issue 28167
+covariant_override_test: CompileTimeError # Issue 28167
+
 # Runtime negative test. No static errors or warnings.
 closure_call_wrong_argument_count_negative_test: skip
 

tests/language/language_dart2js.status

@@ -39,6 +39,17 @@ duplicate_part_test/01: MissingCompileTimeError # Issue 27517
 
 bad_typedef_test/00: Crash # Issue 28214
 
+covariant_test/02: MissingCompileTimeError, OK # Accepts `covariant` for statics/top-level.
+covariant_test/08: MissingCompileTimeError, OK # Accepts `covariant` for statics/top-level.
+covariant_test/12: MissingCompileTimeError, OK # Accepts `covariant` for statics/top-level.
+covariant_test/14: MissingCompileTimeError, OK # Accepts `covariant` for statics/top-level.
+covariant_test/16: MissingCompileTimeError, OK # Accepts `covariant` for statics/top-level.
+covariant_test/22: MissingCompileTimeError, OK # Accepts `covariant` for statics/top-level.
+covariant_test/28: MissingCompileTimeError, OK # Accepts `covariant` for statics/top-level.
+covariant_test/32: MissingCompileTimeError, OK # Accepts `covariant` for statics/top-level.
+covariant_test/34: MissingCompileTimeError, OK # Accepts `covariant` for statics/top-level.
+covariant_test/36: MissingCompileTimeError, OK # Accepts `covariant` for statics/top-level.
+
 [ $compiler == dart2js && $fast_startup ]
 const_evaluation_test/*: Fail # mirrors not supported
 deferred_constraints_constants_test/none: Fail # mirrors not supported

tests/language/language_kernel.status

@@ -89,6 +89,8 @@ vm/debug_break_enabled_vm_test/none: DartkCompileTimeError
 vm/reflect_core_vm_test: DartkCompileTimeError
 vm/regress_27201_test: DartkCompileTimeError
 vm/regress_28325_test: RuntimeError  # Issue 28055.
+covariant_test/none: CompileTimeError # Issue 28166
+covariant_override_test: Crash # Issue 28166
 
 # dartk: JIT failures
 [ $compiler == dartk && $runtime == vm ]