implement Array/String/TypedArray item methods

Bug: v8:10961
Change-Id: I79f8410cac1c949100231d4c57dbea0379e88475
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2441128
Commit-Queue: Gus Caplan <snek@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71279}

BUILD.gn

@@ -1134,6 +1134,7 @@ action("postmortem-metadata") {
 
 torque_files = [
   "src/builtins/aggregate-error.tq",
+  "src/builtins/array-at.tq",
   "src/builtins/array-copywithin.tq",
   "src/builtins/array-every.tq",
   "src/builtins/array-filter.tq",
@@ -1216,6 +1217,7 @@ torque_files = [
   "src/builtins/regexp-split.tq",
   "src/builtins/regexp-test.tq",
   "src/builtins/regexp.tq",
+  "src/builtins/string-at.tq",
   "src/builtins/string-endswith.tq",
   "src/builtins/string-html.tq",
   "src/builtins/string-iterator.tq",
@@ -1229,6 +1231,7 @@ torque_files = [
   "src/builtins/string-trim.tq",
   "src/builtins/symbol.tq",
   "src/builtins/torque-internal.tq",
+  "src/builtins/typed-array-at.tq",
   "src/builtins/typed-array-createtypedarray.tq",
   "src/builtins/typed-array-every.tq",
   "src/builtins/typed-array-entries.tq",

src/builtins/array-at.tq

@@ -0,0 +1,27 @@
+// Copyright 2020 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.
+
+namespace array {
+// https://tc39.es/proposal-item-method/#sec-array.prototype.at
+transitioning javascript builtin ArrayPrototypeAt(
+    js-implicit context: NativeContext, receiver: JSAny)(index: JSAny): JSAny {
+  // 1. Let O be ? ToObject(this value).
+  const o = ToObject_Inline(context, receiver);
+  // 2. Let len be ? LengthOfArrayLike(O).
+  const len = GetLengthProperty(o);
+  // 3. Let relativeIndex be ? ToInteger(index).
+  const relativeIndex = ToInteger_Inline(index);
+  // 4. If relativeIndex ≥ 0, then
+  //   a. Let k be relativeIndex.
+  // 5. Else,
+  //   a. Let k be len + relativeIndex.
+  const k = relativeIndex >= 0 ? relativeIndex : len + relativeIndex;
+  // 6. If k < 0 or k ≥ len, then return undefined.
+  if (k < 0 || k >= len) {
+    return Undefined;
+  }
+  // 7. Return ? Get(O, ! ToString(k)).
+  return GetProperty(o, k);
+}
+}

src/builtins/string-at.tq

@@ -0,0 +1,29 @@
+// Copyright 2020 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.
+
+namespace string {
+// https://tc39.es/proposal-item-method/#sec-string.prototype.at
+transitioning javascript builtin StringPrototypeAt(
+    js-implicit context: NativeContext, receiver: JSAny)(index: JSAny): JSAny {
+  // 1. Let O be ? RequireObjectCoercible(this value).
+  // 2. Let S be ? ToString(O).
+  const s = ToThisString(receiver, 'String.prototype.at');
+  // 3. Let len be the length of S.
+  const len = s.length_smi;
+  // 4. Let relativeIndex be ? ToInteger(index).
+  const relativeIndex = ToInteger_Inline(index);
+  // 5. If relativeIndex ≥ 0, then
+  //   a. Let k be relativeIndex.
+  // 6. Else,
+  //   a. Let k be len + relativeIndex.
+  const k = relativeIndex >= 0 ? relativeIndex : len + relativeIndex;
+  // 7. If k < 0 or k ≥ len, then return undefined.
+  if (k < 0 || k >= len) {
+    return Undefined;
+  }
+  // 8. Return the String value consisting of only the code unit at position k
+  // in S.
+  return StringFromSingleCharCode(StringCharCodeAt(s, Convert<uintptr>(k)));
+}
+}

src/builtins/typed-array-at.tq

@@ -0,0 +1,28 @@
+// Copyright 2020 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.
+
+namespace typed_array {
+// https://tc39.es/proposal-item-method/#sec-%typedarray%.prototype.at
+transitioning javascript builtin TypedArrayPrototypeAt(
+    js-implicit context: NativeContext, receiver: JSAny)(index: JSAny): JSAny {
+  // 1. Let O be the this value.
+  // 2. Perform ? ValidateTypedArray(O).
+  const o = ValidateTypedArray(context, receiver, '%TypedArray%.prototype.at');
+  // 3. Let len be O.[[ArrayLength]].
+  const len = Convert<Number>(o.length);
+  // 4. Let relativeIndex be ? ToInteger(index).
+  const relativeIndex = ToInteger_Inline(index);
+  // 5. If relativeIndex ≥ 0, then
+  //   a. Let k be relativeIndex.
+  // 6. Else,
+  //   a. Let k be len + relativeIndex.
+  const k = relativeIndex >= 0 ? relativeIndex : len + relativeIndex;
+  // 7. If k < 0 or k ≥ len, then return undefined.
+  if (k < 0 || k >= len) {
+    return Undefined;
+  }
+  // 8. Return ? Get(O, ! ToString(k)).
+  return GetProperty(o, k);
+}
+}

src/debug/debug-evaluate.cc

@@ -567,6 +567,7 @@ DebugInfo::SideEffectState BuiltinGetSideEffectState(Builtins::Name id) {
     case Builtins::kArrayIndexOf:
     case Builtins::kArrayPrototypeValues:
     case Builtins::kArrayIncludes:
+    case Builtins::kArrayPrototypeAt:
     case Builtins::kArrayPrototypeEntries:
     case Builtins::kArrayPrototypeFill:
     case Builtins::kArrayPrototypeFind:
@@ -592,6 +593,7 @@ DebugInfo::SideEffectState BuiltinGetSideEffectState(Builtins::Name id) {
     case Builtins::kTrace:
     // TypedArray builtins.
     case Builtins::kTypedArrayConstructor:
+    case Builtins::kTypedArrayPrototypeAt:
     case Builtins::kTypedArrayPrototypeBuffer:
     case Builtins::kTypedArrayPrototypeByteLength:
     case Builtins::kTypedArrayPrototypeByteOffset:
@@ -759,6 +761,7 @@ DebugInfo::SideEffectState BuiltinGetSideEffectState(Builtins::Name id) {
     case Builtins::kStringFromCodePoint:
     case Builtins::kStringConstructor:
     case Builtins::kStringPrototypeAnchor:
+    case Builtins::kStringPrototypeAt:
     case Builtins::kStringPrototypeBig:
     case Builtins::kStringPrototypeBlink:
     case Builtins::kStringPrototypeBold:

src/flags/flag-definitions.h

@@ -253,7 +253,8 @@ DEFINE_IMPLICATION(harmony_weak_refs_with_cleanup_some, harmony_weak_refs)
   V(harmony_weak_refs_with_cleanup_some,                                       \
     "harmony weak references with FinalizationRegistry.prototype.cleanupSome") \
   V(harmony_regexp_match_indices, "harmony regexp match indices")              \
-  V(harmony_import_assertions, "harmony import assertions")
+  V(harmony_import_assertions, "harmony import assertions")                    \
+  V(harmony_relative_indexing_methods, "harmony relative indexing methods")
 
 #ifdef V8_INTL_SUPPORT
 #define HARMONY_INPROGRESS(V)                       \

src/init/bootstrapper.cc

@@ -4391,6 +4391,40 @@ void Genesis::InitializeGlobal_regexp_linear_flag() {
   native_context()->set_regexp_prototype_map(regexp_prototype->map());
 }
 
+void Genesis::InitializeGlobal_harmony_relative_indexing_methods() {
+  if (!FLAG_harmony_relative_indexing_methods) return;
+
+  {
+    Handle<JSFunction> array_function(native_context()->array_function(),
+                                      isolate());
+    Handle<JSObject> array_prototype(
+        JSObject::cast(array_function->instance_prototype()), isolate());
+
+    SimpleInstallFunction(isolate(), array_prototype, "at",
+                          Builtins::kArrayPrototypeAt, 1, true);
+  }
+
+  {
+    Handle<JSFunction> string_function(native_context()->string_function(),
+                                       isolate());
+    Handle<JSObject> string_prototype(
+        JSObject::cast(string_function->instance_prototype()), isolate());
+
+    SimpleInstallFunction(isolate(), string_prototype, "at",
+                          Builtins::kStringPrototypeAt, 1, true);
+  }
+
+  {
+    Handle<JSFunction> typed_array_function(
+        native_context()->typed_array_function(), isolate());
+    Handle<JSObject> typed_array_prototype(
+        JSObject::cast(typed_array_function->instance_prototype()), isolate());
+
+    SimpleInstallFunction(isolate(), typed_array_prototype, "at",
+                          Builtins::kTypedArrayPrototypeAt, 1, true);
+  }
+}
+
 #ifdef V8_INTL_SUPPORT
 
 void Genesis::InitializeGlobal_harmony_intl_segmenter() {

test/mjsunit/harmony/relative-indexing-methods.js

@@ -0,0 +1,47 @@
+// Copyright 2020 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-relative-indexing-methods --allow-natives-syntax
+
+'use strict';
+
+[
+  [1, 2, 3],
+  '123',
+  new Uint8Array([1, 2, 3]),
+].forEach((v) => {
+  assertEquals(v.at(0), v[0]);
+  assertEquals(v.at(-1), v[2]);
+  assertEquals(v.at(-4), undefined);
+  assertEquals(v.at(3), undefined);
+  assertEquals(v.at(1337), undefined);
+  assertEquals(v.at(-Infinity), undefined);
+  assertEquals(v.at(Infinity), undefined);
+  assertEquals(v.at(NaN), v[0]);
+  assertEquals(v.at(undefined), v[0])
+  assertEquals(v.at(), v[0]);
+});
+
+{
+  const props = ['length', '2'];
+  const proxy = new Proxy([1, 2, 3], {
+    get(t, p, r) {
+      assertEquals(p, props.shift());
+      return Reflect.get(t, p, r);
+    }
+  });
+  assertEquals(Array.prototype.at.call(proxy, -1), 3);
+}
+
+assertThrows(() => {
+  Uint8Array.prototype.at.call({});
+}, TypeError);
+
+{
+  const a = new Uint8Array([1, 2, 3]);
+  %ArrayBufferDetach(a.buffer);
+  assertThrows(() => {
+    a.at(0);
+  }, TypeError);
+}

tools/v8heapconst.py

@@ -449,27 +449,27 @@ KNOWN_OBJECTS = {
   ("old_space", 0x02a71): "StringSplitCache",
   ("old_space", 0x02e79): "RegExpMultipleCache",
   ("old_space", 0x03281): "BuiltinsConstantsTable",
-  ("old_space", 0x03661): "AsyncFunctionAwaitRejectSharedFun",
-  ("old_space", 0x03689): "AsyncFunctionAwaitResolveSharedFun",
-  ("old_space", 0x036b1): "AsyncGeneratorAwaitRejectSharedFun",
-  ("old_space", 0x036d9): "AsyncGeneratorAwaitResolveSharedFun",
-  ("old_space", 0x03701): "AsyncGeneratorYieldResolveSharedFun",
-  ("old_space", 0x03729): "AsyncGeneratorReturnResolveSharedFun",
-  ("old_space", 0x03751): "AsyncGeneratorReturnClosedRejectSharedFun",
-  ("old_space", 0x03779): "AsyncGeneratorReturnClosedResolveSharedFun",
-  ("old_space", 0x037a1): "AsyncIteratorValueUnwrapSharedFun",
-  ("old_space", 0x037c9): "PromiseAllResolveElementSharedFun",
-  ("old_space", 0x037f1): "PromiseAllSettledResolveElementSharedFun",
-  ("old_space", 0x03819): "PromiseAllSettledRejectElementSharedFun",
-  ("old_space", 0x03841): "PromiseAnyRejectElementSharedFun",
-  ("old_space", 0x03869): "PromiseCapabilityDefaultRejectSharedFun",
-  ("old_space", 0x03891): "PromiseCapabilityDefaultResolveSharedFun",
-  ("old_space", 0x038b9): "PromiseCatchFinallySharedFun",
-  ("old_space", 0x038e1): "PromiseGetCapabilitiesExecutorSharedFun",
-  ("old_space", 0x03909): "PromiseThenFinallySharedFun",
-  ("old_space", 0x03931): "PromiseThrowerFinallySharedFun",
-  ("old_space", 0x03959): "PromiseValueThunkFinallySharedFun",
-  ("old_space", 0x03981): "ProxyRevokeSharedFun",
+  ("old_space", 0x03669): "AsyncFunctionAwaitRejectSharedFun",
+  ("old_space", 0x03691): "AsyncFunctionAwaitResolveSharedFun",
+  ("old_space", 0x036b9): "AsyncGeneratorAwaitRejectSharedFun",
+  ("old_space", 0x036e1): "AsyncGeneratorAwaitResolveSharedFun",
+  ("old_space", 0x03709): "AsyncGeneratorYieldResolveSharedFun",
+  ("old_space", 0x03731): "AsyncGeneratorReturnResolveSharedFun",
+  ("old_space", 0x03759): "AsyncGeneratorReturnClosedRejectSharedFun",
+  ("old_space", 0x03781): "AsyncGeneratorReturnClosedResolveSharedFun",
+  ("old_space", 0x037a9): "AsyncIteratorValueUnwrapSharedFun",
+  ("old_space", 0x037d1): "PromiseAllResolveElementSharedFun",
+  ("old_space", 0x037f9): "PromiseAllSettledResolveElementSharedFun",
+  ("old_space", 0x03821): "PromiseAllSettledRejectElementSharedFun",
+  ("old_space", 0x03849): "PromiseAnyRejectElementSharedFun",
+  ("old_space", 0x03871): "PromiseCapabilityDefaultRejectSharedFun",
+  ("old_space", 0x03899): "PromiseCapabilityDefaultResolveSharedFun",
+  ("old_space", 0x038c1): "PromiseCatchFinallySharedFun",
+  ("old_space", 0x038e9): "PromiseGetCapabilitiesExecutorSharedFun",
+  ("old_space", 0x03911): "PromiseThenFinallySharedFun",
+  ("old_space", 0x03939): "PromiseThrowerFinallySharedFun",
+  ("old_space", 0x03961): "PromiseValueThunkFinallySharedFun",
+  ("old_space", 0x03989): "ProxyRevokeSharedFun",
 }
 
 # Lower 32 bits of first page addresses for various heap spaces.