[esnext] Rename `Array#flatten` to `flat`

The TC39 committee reached consensus to rename `flatten` to `flat`
during the May 22nd meeting. The corresponding patch to the proposal
is here:

https://github.com/tc39/proposal-flatMap/commit/093eacc7fe0906e70f7626bf6c7d6e9dfc53cce9

Bug: v8:7220
Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: Ie8049ae4d4589a4ae7fe3d203053cef798c135e4
Reviewed-on: https://chromium-review.googlesource.com/1069467Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53294}

src/bootstrapper.cc

@@ -4276,13 +4276,13 @@ void Genesis::InitializeGlobal_harmony_array_prototype_values() {
                         NONE);
 }
 
-void Genesis::InitializeGlobal_harmony_array_flatten() {
-  if (!FLAG_harmony_array_flatten) return;
+void Genesis::InitializeGlobal_harmony_array_flat() {
+  if (!FLAG_harmony_array_flat) return;
   Handle<JSFunction> array_constructor(native_context()->array_function());
   Handle<JSObject> array_prototype(
       JSObject::cast(array_constructor->instance_prototype()));
-  SimpleInstallFunction(array_prototype, "flatten",
-                        Builtins::kArrayPrototypeFlatten, 0, false, DONT_ENUM);
+  SimpleInstallFunction(array_prototype, "flat", Builtins::kArrayPrototypeFlat,
+                        0, false, DONT_ENUM);
   SimpleInstallFunction(array_prototype, "flatMap",
                         Builtins::kArrayPrototypeFlatMap, 1, false, DONT_ENUM);
 }

src/builtins/builtins-array-gen.cc

@@ -3921,8 +3921,8 @@ TF_BUILTIN(FlatMapIntoArray, ArrayFlattenAssembler) {
                           mapper_function, this_arg));
 }
 
-// https://tc39.github.io/proposal-flatMap/#sec-Array.prototype.flatten
-TF_BUILTIN(ArrayPrototypeFlatten, CodeStubAssembler) {
+// https://tc39.github.io/proposal-flatMap/#sec-Array.prototype.flat
+TF_BUILTIN(ArrayPrototypeFlat, CodeStubAssembler) {
   Node* const argc =
       ChangeInt32ToIntPtr(Parameter(BuiltinDescriptor::kArgumentsCount));
   CodeStubArguments args(this, argc);

src/builtins/builtins-definitions.h

@@ -360,8 +360,8 @@ namespace internal {
   TFS(FlattenIntoArray, kTarget, kSource, kSourceLength, kStart, kDepth)       \
   TFS(FlatMapIntoArray, kTarget, kSource, kSourceLength, kStart, kDepth,       \
       kMapperFunction, kThisArg)                                               \
-  /* https://tc39.github.io/proposal-flatMap/#sec-Array.prototype.flatten */   \
-  TFJ(ArrayPrototypeFlatten, SharedFunctionInfo::kDontAdaptArgumentsSentinel)  \
+  /* https://tc39.github.io/proposal-flatMap/#sec-Array.prototype.flat */      \
+  TFJ(ArrayPrototypeFlat, SharedFunctionInfo::kDontAdaptArgumentsSentinel)     \
   /* https://tc39.github.io/proposal-flatMap/#sec-Array.prototype.flatMap */   \
   TFJ(ArrayPrototypeFlatMap, SharedFunctionInfo::kDontAdaptArgumentsSentinel)  \
                                                                                \

src/flag-definitions.h

@@ -212,7 +212,7 @@ DEFINE_IMPLICATION(harmony_class_fields, harmony_private_fields)
   V(harmony_do_expressions, "harmony do-expressions")                 \
   V(harmony_class_fields, "harmony fields in class literals")         \
   V(harmony_static_fields, "harmony static fields in class literals") \
-  V(harmony_array_flatten, "harmony Array.prototype.flat{ten,Map}")
+  V(harmony_array_flat, "harmony Array.prototype.{flat,flatMap}")
 
 #ifdef V8_INTL_SUPPORT
 #define HARMONY_INPROGRESS(V) \

test/mjsunit/harmony/array-flat.js

+// Copyright 2018 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-array-flat
+
+assertEquals(Array.prototype.flat.length, 0);
+assertEquals(Array.prototype.flat.name, 'flat');
+
+const input = [1, [2], [[3]]];
+
+assertEquals(input.flat(),          [1, 2, [3]]);
+assertEquals(input.flat(1),         [1, 2, [3]]);
+assertEquals(input.flat(true),      [1, 2, [3]]);
+assertEquals(input.flat(undefined), [1, 2, [3]]);
+
+assertEquals(input.flat(-Infinity), [1, [2], [[3]]]);
+assertEquals(input.flat(-1),        [1, [2], [[3]]]);
+assertEquals(input.flat(-0),        [1, [2], [[3]]]);
+assertEquals(input.flat(0),         [1, [2], [[3]]]);
+assertEquals(input.flat(false),     [1, [2], [[3]]]);
+assertEquals(input.flat(null),      [1, [2], [[3]]]);
+assertEquals(input.flat(''),        [1, [2], [[3]]]);
+assertEquals(input.flat('foo'),     [1, [2], [[3]]]);
+assertEquals(input.flat(/./),       [1, [2], [[3]]]);
+assertEquals(input.flat([]),        [1, [2], [[3]]]);
+assertEquals(input.flat({}),        [1, [2], [[3]]]);
+assertEquals(
+  input.flat(new Proxy({}, {})),    [1, [2], [[3]]]);
+assertEquals(input.flat((x) => x),  [1, [2], [[3]]]);
+assertEquals(
+  input.flat(String),               [1, [2], [[3]]]);
+
+assertEquals(input.flat(2),         [1, 2, 3]);
+assertEquals(input.flat(Infinity),  [1, 2, 3]);
+
+assertThrows(() => { input.flat(Symbol()); }, TypeError);
+assertThrows(() => { input.flat(Object.create(null)); }, TypeError);

test/mjsunit/harmony/array-flatMap.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --harmony-array-flatten --allow-natives-syntax
+// Flags: --harmony-array-flat --allow-natives-syntax
 
 assertEquals(Array.prototype.flatMap.length, 1);
 assertEquals(Array.prototype.flatMap.name, 'flatMap');

test/mjsunit/harmony/array-flatten.js

-// Copyright 2018 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Flags: --harmony-array-flatten
-
-assertEquals(Array.prototype.flatten.length, 0);
-assertEquals(Array.prototype.flatten.name, 'flatten');
-
-const input = [1, [2], [[3]]];
-
-assertEquals(input.flatten(),          [1, 2, [3]]);
-assertEquals(input.flatten(1),         [1, 2, [3]]);
-assertEquals(input.flatten(true),      [1, 2, [3]]);
-assertEquals(input.flatten(undefined), [1, 2, [3]]);
-
-assertEquals(input.flatten(-Infinity), [1, [2], [[3]]]);
-assertEquals(input.flatten(-1),        [1, [2], [[3]]]);
-assertEquals(input.flatten(-0),        [1, [2], [[3]]]);
-assertEquals(input.flatten(0),         [1, [2], [[3]]]);
-assertEquals(input.flatten(false),     [1, [2], [[3]]]);
-assertEquals(input.flatten(null),      [1, [2], [[3]]]);
-assertEquals(input.flatten(''),        [1, [2], [[3]]]);
-assertEquals(input.flatten('foo'),     [1, [2], [[3]]]);
-assertEquals(input.flatten(/./),       [1, [2], [[3]]]);
-assertEquals(input.flatten([]),        [1, [2], [[3]]]);
-assertEquals(input.flatten({}),        [1, [2], [[3]]]);
-assertEquals(
-  input.flatten(new Proxy({}, {})),    [1, [2], [[3]]]);
-assertEquals(input.flatten((x) => x),  [1, [2], [[3]]]);
-assertEquals(
-  input.flatten(String),               [1, [2], [[3]]]);
-
-assertEquals(input.flatten(2),         [1, 2, 3]);
-assertEquals(input.flatten(Infinity),  [1, 2, 3]);
-
-assertThrows(() => { input.flatten(Symbol()); }, TypeError);
-assertThrows(() => { input.flatten(Object.create(null)); }, TypeError);

test/test262/testcfg.py

@@ -49,14 +49,18 @@ FEATURE_FLAGS = {
   'class-fields-public': '--harmony-public-fields',
   'optional-catch-binding': '--harmony-optional-catch-binding',
   'class-fields-private': '--harmony-private-fields',
-  'Array.prototype.flatten': '--harmony-array-flatten',
-  'Array.prototype.flatMap': '--harmony-array-flatten',
+  'Array.prototype.flat': '--harmony-array-flat',
+  'Array.prototype.flatMap': '--harmony-array-flat',
   'String.prototype.matchAll': '--harmony-string-matchall',
   'Symbol.matchAll': '--harmony-string-matchall',
   'numeric-separator-literal': '--harmony-numeric-separator',
 }
 
-SKIPPED_FEATURES = set([])
+SKIPPED_FEATURES = set([
+  # `flatten` has been renamed to `flat`. TODO(mths): Remove this once
+  # https://github.com/tc39/test262/pull/1569 is rolled in.
+  'Array.prototype.flatten',
+])
 
 DATA = os.path.join(os.path.dirname(os.path.abspath(__file__)), "data")