[esnext] Implement Array.prototype.{flatten,flatMap} 🥙

Proposal repo: https://tc39.github.io/proposal-flatMap/

Bug: v8:7220
Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: I61661fc6d5c39d084ce5c96a9e150e5c26799e2d
Also-By: bmeurer@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/957043
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51967}

src/bootstrapper.cc

@@ -4251,6 +4251,17 @@ void Genesis::InitializeGlobal_harmony_array_prototype_values() {
                         NONE);
 }
 
+void Genesis::InitializeGlobal_harmony_array_flatten() {
+  if (!FLAG_harmony_array_flatten) 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, "flatMap",
+                        Builtins::kArrayPrototypeFlatMap, 1, false, DONT_ENUM);
+}
+
 void Genesis::InitializeGlobal_harmony_promise_finally() {
   if (!FLAG_harmony_promise_finally) return;
 

src/builtins/builtins-definitions.h

@@ -367,6 +367,14 @@ namespace internal {
   TFJ(ArrayPrototypeValues, 0)                                                 \
   /* ES6 #sec-%arrayiteratorprototype%.next */                                 \
   TFJ(ArrayIteratorPrototypeNext, 0)                                           \
+  /* https://tc39.github.io/proposal-flatMap/#sec-FlattenIntoArray */          \
+  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.flatMap */   \
+  TFJ(ArrayPrototypeFlatMap, SharedFunctionInfo::kDontAdaptArgumentsSentinel)  \
                                                                                \
   /* ArrayBuffer */                                                            \
   /* ES #sec-arraybuffer-constructor */                                        \

src/code-stub-assembler.cc

@@ -6174,7 +6174,8 @@ TNode<Number> CodeStubAssembler::ToLength_Inline(SloppyTNode<Context> context,
 }
 
 TNode<Number> CodeStubAssembler::ToInteger_Inline(
-    TNode<Context> context, TNode<Object> input, ToIntegerTruncationMode mode) {
+    SloppyTNode<Context> context, SloppyTNode<Object> input,
+    ToIntegerTruncationMode mode) {
   Builtins::Name builtin = (mode == kNoTruncation)
                                ? Builtins::kToInteger
                                : Builtins::kToInteger_TruncateMinusZero;
@@ -10022,7 +10023,7 @@ void CodeStubAssembler::BranchIfSameValue(Node* lhs, Node* rhs, Label* if_true,
 }
 
 TNode<Oddball> CodeStubAssembler::HasProperty(SloppyTNode<HeapObject> object,
-                                              SloppyTNode<Name> key,
+                                              SloppyTNode<Object> key,
                                               SloppyTNode<Context> context,
                                               HasPropertyLookupMode mode) {
   Label call_runtime(this, Label::kDeferred), return_true(this),

src/code-stub-assembler.h

@@ -1315,7 +1315,8 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
                                 SloppyTNode<Object> input);
 
   // ES6 7.1.4 ToInteger ( argument )
-  TNode<Number> ToInteger_Inline(TNode<Context> context, TNode<Object> input,
+  TNode<Number> ToInteger_Inline(SloppyTNode<Context> context,
+                                 SloppyTNode<Object> input,
                                  ToIntegerTruncationMode mode = kNoTruncation);
   TNode<Number> ToInteger(SloppyTNode<Context> context,
                           SloppyTNode<Object> input,
@@ -1910,7 +1911,7 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
   enum HasPropertyLookupMode { kHasProperty, kForInHasProperty };
 
   TNode<Oddball> HasProperty(SloppyTNode<HeapObject> object,
-                             SloppyTNode<Name> key,
+                             SloppyTNode<Object> key,
                              SloppyTNode<Context> context,
                              HasPropertyLookupMode mode);
 

src/flag-definitions.h

@@ -212,7 +212,8 @@ DEFINE_IMPLICATION(harmony_class_fields, harmony_private_fields)
   V(harmony_array_prototype_values, "harmony Array.prototype.values") \
   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_static_fields, "harmony static fields in class literals") \
+  V(harmony_array_flatten, "harmony Array.prototype.flat{ten,Map}")
 
 // Features that are complete (but still behind --harmony/es-staging flag).
 #define HARMONY_STAGED(V)                                               \

src/messages.h

@@ -343,6 +343,7 @@ class ErrorUtils : public AllStatic {
   T(IteratorSymbolNonCallable, "Found non-callable @@iterator")                \
   T(IteratorValueNotAnObject, "Iterator value % is not an entry object")       \
   T(LanguageID, "Language ID should be string or object.")                     \
+  T(MapperFunctionNonCallable, "flatMap mapper function is not callable")      \
   T(MethodCalledOnWrongObject,                                                 \
     "Method % called on a non-object or on a wrong type of object.")           \
   T(MethodInvokedOnNullOrUndefined,                                            \
@@ -643,6 +644,9 @@ class ErrorUtils : public AllStatic {
   T(NoCatchOrFinally, "Missing catch or finally after try")                    \
   T(NotIsvar, "builtin %%IS_VAR: not a variable")                              \
   T(ParamAfterRest, "Rest parameter must be last formal parameter")            \
+  T(FlattenPastSafeLength,                                                     \
+    "Flattening % elements on an array-like of length % "                      \
+    "is disallowed, as the total surpasses 2**53-1")                           \
   T(PushPastSafeLength,                                                        \
     "Pushing % elements on an array-like of length % "                         \
     "is disallowed, as the total surpasses 2**53-1")                           \

test/cctest/interpreter/bytecode_expectations/AsyncGenerators.golden

@@ -367,7 +367,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(18),
                 B(LdaConstant), U8(15),
                 B(Star), R(19),

test/cctest/interpreter/bytecode_expectations/ForAwaitOf.golden

@@ -124,7 +124,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(19),
                 B(LdaConstant), U8(12),
                 B(Star), R(20),
@@ -378,7 +378,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(19),
                 B(LdaConstant), U8(12),
                 B(Star), R(20),
@@ -654,7 +654,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(19),
                 B(LdaConstant), U8(12),
                 B(Star), R(20),
@@ -886,7 +886,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(17),
                 B(LdaConstant), U8(10),
                 B(Star), R(18),

test/cctest/interpreter/bytecode_expectations/ForOf.golden

@@ -86,7 +86,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(12),
                 B(LdaConstant), U8(8),
                 B(Star), R(13),
@@ -220,7 +220,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(13),
                 B(LdaConstant), U8(8),
                 B(Star), R(14),
@@ -366,7 +366,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(12),
                 B(LdaConstant), U8(8),
                 B(Star), R(13),
@@ -502,7 +502,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(11),
                 B(LdaConstant), U8(10),
                 B(Star), R(12),

test/cctest/interpreter/bytecode_expectations/ForOfLoop.golden

@@ -90,7 +90,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(14),
                 B(LdaConstant), U8(7),
                 B(Star), R(15),
@@ -261,7 +261,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(14),
                 B(LdaConstant), U8(11),
                 B(Star), R(15),
@@ -408,7 +408,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(12),
                 B(LdaConstant), U8(9),
                 B(Star), R(13),
@@ -503,7 +503,7 @@ bytecodes: [
                 B(JumpIfUndefined), U8(6),
                 B(Ldar), R(6),
                 B(JumpIfNotNull), U8(16),
-                B(LdaSmi), I8(76),
+                B(LdaSmi), I8(77),
                 B(Star), R(18),
                 B(LdaConstant), U8(4),
                 B(Star), R(19),
@@ -559,7 +559,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(17),
                 B(LdaConstant), U8(9),
                 B(Star), R(18),
@@ -713,7 +713,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(16),
                 B(LdaConstant), U8(10),
                 B(Star), R(17),
@@ -882,7 +882,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(15),
                 B(LdaConstant), U8(13),
                 B(Star), R(16),
@@ -1037,7 +1037,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(21),
                 B(LdaConstant), U8(7),
                 B(Star), R(22),
@@ -1253,7 +1253,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(20),
                 B(LdaConstant), U8(8),
                 B(Star), R(21),

test/cctest/interpreter/bytecode_expectations/Generators.golden

@@ -204,7 +204,7 @@ bytecodes: [
                 B(TestTypeOf), U8(6),
                 B(JumpIfFalse), U8(4),
                 B(Jump), U8(18),
-                B(Wide), B(LdaSmi), I16(146),
+                B(Wide), B(LdaSmi), I16(147),
                 B(Star), R(14),
                 B(LdaConstant), U8(14),
                 B(Star), R(15),

test/cctest/interpreter/bytecode_expectations/StandardForLoop.golden

@@ -231,7 +231,7 @@ bytecodes: [
                 B(JumpIfUndefined), U8(6),
                 B(Ldar), R(3),
                 B(JumpIfNotNull), U8(16),
-                B(LdaSmi), I8(76),
+                B(LdaSmi), I8(77),
                 B(Star), R(4),
                 B(LdaConstant), U8(1),
                 B(Star), R(5),

test/mjsunit/harmony/array-flatMap.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 --allow-natives-syntax
+
+assertEquals(Array.prototype.flatMap.length, 1);
+assertEquals(Array.prototype.flatMap.name, 'flatMap');
+
+assertEquals(
+  [1, 2, 3, 4].flatMap((element) => [element, element ** 2]),
+  [1, 1, 2, 4, 3, 9, 4, 16]
+);
+assertEquals(
+  [1, 2, 3, 4].flatMap((element) => [[element, element ** 2]]),
+  [[1, 1], [2, 4], [3, 9], [4, 16]]
+);
+
+const elements = new Set([
+  -Infinity,
+  -1,
+  -0,
+  +0,
+  +1,
+  Infinity,
+  null,
+  undefined,
+  true,
+  false,
+  '',
+  'foo',
+  /./,
+  [],
+  {},
+  Object.create(null),
+  new Proxy({}, {}),
+  Symbol(),
+  x => x ** 2,
+  String
+]);
+
+for (const value of elements) {
+  assertEquals(
+    [value].flatMap((element) => [element, element]),
+    [value, value]
+  );
+}
+
+const array = [42];
+assertEquals(
+  [array].flatMap((element) => [element, element]),
+  [array, array]
+);
+
+const nonCallables = new Set([
+  -Infinity,
+  -1,
+  -0,
+  +0,
+  +1,
+  Infinity,
+  null,
+  undefined,
+  true,
+  false,
+  '',
+  'foo',
+  /./,
+  [],
+  {},
+  Object.create(null),
+  new Proxy({}, {}),
+  Symbol(),
+]);
+for (const nonCallable of nonCallables) {
+  assertThrows(() => {
+    [].flatMap(nonCallable);
+  }, TypeError);
+}
+
+const object = {
+  foo: 42,
+  get length() {
+    object.foo = 0;
+  }
+};
+const result = [object].flatMap((element) => [element, element]);
+%HeapObjectVerify(result);
+assertEquals(result, [object, object]);
+assertEquals(result[0].foo, 42);
+
+assertThrows(() => {
+  Array.prototype.flatMap.call(null, (element) => element);
+}, TypeError);
+assertThrows(() => {
+  Array.prototype.flatMap.call(undefined, (element) => element);
+}, TypeError);
+
+assertEquals(
+  Array.prototype.flatMap.call(
+    {
+      length: 1,
+      0: 'a',
+      1: 'b',
+    },
+    (element) => element
+  ),
+  ['a']
+);
+assertEquals(
+  Array.prototype.flatMap.call(
+    {
+      length: 2,
+      0: 'a',
+      1: 'b',
+    },
+    (element) => element
+  ),
+  ['a', 'b']
+);

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

@@ -50,11 +50,12 @@ 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',
   'numeric-separator-literal': '--harmony-numeric-separator',
 }
 
-SKIPPED_FEATURES = set(['Array.prototype.flatten',
-                        'Array.prototype.flatMap'])
+SKIPPED_FEATURES = set([])
 
 DATA = os.path.join(os.path.dirname(os.path.abspath(__file__)), "data")
 ARCHIVE = DATA + ".tar"

tools/presubmit.py

@@ -60,7 +60,9 @@ LINT_RULES = """
 -build/header_guard
 -build/include_what_you_use
 -readability/fn_size
+-readability/multiline_comment
 -runtime/references
+-whitespace/comments
 """.split()
 
 LINT_OUTPUT_PATTERN = re.compile(r'^.+[:(]\d+[:)]|^Done processing')