Support at methods for Array, TypedArray, and String

Summary:
Solve the gap raised in facebook#823. Add support for `.prototype.add` for Array, TypedArray, and String. The implementation closely follows the spec.

Original Author: fbmal7
Original Git: 8d3933c1a0f758ee3ee3db4c9e02c4106d5bf70b

Original Reviewed By: jpporto

Original Revision: D40497162

Reviewed By: tmikov

Differential Revision: D41240776

fbshipit-source-id: 99ec74d26d2e81b8f47ee1ad51fb8f95e2f26326

include/hermes/VM/NativeFunctions.def

@@ -27,6 +27,7 @@ NATIVE_FUNCTION(arrayIsArray)
 NATIVE_FUNCTION(arrayFrom)
 NATIVE_FUNCTION(arrayOf)
 NATIVE_FUNCTION(arrayIteratorPrototypeNext)
+NATIVE_FUNCTION(arrayPrototypeAt)
 NATIVE_FUNCTION(arrayPrototypeConcat)
 NATIVE_FUNCTION(arrayPrototypeForEach)
 NATIVE_FUNCTION(arrayPrototypeIterator)
@@ -315,6 +316,7 @@ NATIVE_FUNCTION(stringRaw)
 NATIVE_FUNCTION(stringFromCharCode)
 NATIVE_FUNCTION(stringFromCodePoint)
 NATIVE_FUNCTION(stringIteratorPrototypeNext)
+NATIVE_FUNCTION(stringPrototypeAt)
 NATIVE_FUNCTION(stringPrototypeCharCodeAt)
 NATIVE_FUNCTION(stringPrototypeCodePointAt)
 NATIVE_FUNCTION(stringPrototypeConcat)
@@ -356,6 +358,7 @@ NATIVE_FUNCTION(throwTypeError)
 NATIVE_FUNCTION(typedArrayBaseConstructor)
 NATIVE_FUNCTION(typedArrayFrom)
 NATIVE_FUNCTION(typedArrayOf)
+NATIVE_FUNCTION(typedArrayPrototypeAt)
 NATIVE_FUNCTION(typedArrayPrototypeBuffer)
 NATIVE_FUNCTION(typedArrayPrototypeByteLength)
 NATIVE_FUNCTION(typedArrayPrototypeByteOffset)

include/hermes/VM/PredefinedStrings.def

@@ -173,6 +173,7 @@ STR(isToplevel, "isToplevel")
 STR(Array, "Array")
 STR(ArrayIterator, "Array Iterator")
 STR(isArray, "isArray")
+STR(at, "at")
 STR(join, "join")
 STR(push, "push")
 STR(pop, "pop")

lib/VM/JSLib/Array.cpp

@@ -45,6 +45,13 @@ Handle<JSObject> createArrayConstructor(Runtime &runtime) {
       nullptr,
       arrayPrototypeToLocaleString,
       0);
+  defineMethod(
+      runtime,
+      arrayPrototype,
+      Predefined::getSymbolID(Predefined::at),
+      nullptr,
+      arrayPrototypeAt,
+      1);
   defineMethod(
       runtime,
       arrayPrototype,
@@ -534,6 +541,78 @@ arrayPrototypeToLocaleString(void *, Runtime &runtime, NativeArgs args) {
   return HermesValue::encodeStringValue(*builder->getStringPrimitive());
 }
 
+// 23.1.3.1
+CallResult<HermesValue>
+arrayPrototypeAt(void *, Runtime &runtime, NativeArgs args) {
+  GCScope gcScope(runtime);
+  // 1. Let O be ? ToObject(this value).
+  auto objRes = toObject(runtime, args.getThisHandle());
+  if (LLVM_UNLIKELY(objRes == ExecutionStatus::EXCEPTION)) {
+    return ExecutionStatus::EXCEPTION;
+  }
+  auto O = runtime.makeHandle<JSObject>(objRes.getValue());
+
+  // 2. Let len be ? LengthOfArrayLike(O).
+  Handle<JSArray> jsArr = Handle<JSArray>::dyn_vmcast(O);
+  uint32_t len = 0;
+  if (LLVM_LIKELY(jsArr)) {
+    // Fast path for getting the length.
+    len = JSArray::getLength(jsArr.get(), runtime);
+  } else {
+    // Slow path
+    CallResult<PseudoHandle<>> propRes = JSObject::getNamed_RJS(
+        O, runtime, Predefined::getSymbolID(Predefined::length));
+    if (LLVM_UNLIKELY(propRes == ExecutionStatus::EXCEPTION)) {
+      return ExecutionStatus::EXCEPTION;
+    }
+    auto lenRes = toLength(runtime, runtime.makeHandle(std::move(*propRes)));
+    if (LLVM_UNLIKELY(lenRes == ExecutionStatus::EXCEPTION)) {
+      return ExecutionStatus::EXCEPTION;
+    }
+    len = lenRes->getNumber();
+  }
+
+  // 3. Let relativeIndex be ? ToIntegerOrInfinity(index).
+  auto idx = args.getArgHandle(0);
+  auto relativeIndexRes = toIntegerOrInfinity(runtime, idx);
+  if (relativeIndexRes == ExecutionStatus::EXCEPTION) {
+    return ExecutionStatus::EXCEPTION;
+  }
+  const double relativeIndex = relativeIndexRes->getNumber();
+
+  double k;
+  // 4. If relativeIndex ≥ 0, then
+  if (relativeIndex >= 0) {
+    // a. Let k be relativeIndex.
+    k = relativeIndex;
+  } else {
+    // 5. Else,
+    // a. Let k be len + relativeIndex.
+    k = len + relativeIndex;
+  }
+
+  // 6. If k < 0 or k ≥ len, return undefined.
+  if (k < 0 || k >= len) {
+    return HermesValue::encodeUndefinedValue();
+  }
+
+  // 7. Return ? Get(O, ! ToString(𝔽(k))).
+  if (LLVM_LIKELY(jsArr)) {
+    const SmallHermesValue elm = jsArr->at(runtime, k);
+    if (elm.isEmpty()) {
+      return HermesValue::encodeUndefinedValue();
+    } else {
+      return elm.unboxToHV(runtime);
+    }
+  }
+  CallResult<PseudoHandle<>> propRes = JSObject::getComputed_RJS(
+      O, runtime, runtime.makeHandle(HermesValue::encodeDoubleValue(k)));
+  if (LLVM_UNLIKELY(propRes == ExecutionStatus::EXCEPTION)) {
+    return ExecutionStatus::EXCEPTION;
+  }
+  return propRes->getHermesValue();
+}
+
 CallResult<HermesValue>
 arrayPrototypeConcat(void *, Runtime &runtime, NativeArgs args) {
   GCScope gcScope(runtime);

lib/VM/JSLib/String.cpp

@@ -55,6 +55,13 @@ Handle<JSObject> createStringConstructor(Runtime &runtime) {
       ctx,
       stringPrototypeToString,
       0);
+  defineMethod(
+      runtime,
+      stringPrototype,
+      Predefined::getSymbolID(Predefined::at),
+      ctx,
+      stringPrototypeAt,
+      1);
   defineMethod(
       runtime,
       stringPrototype,
@@ -564,6 +571,59 @@ CallResult<HermesValue> stringRaw(void *, Runtime &runtime, NativeArgs args) {
 //===----------------------------------------------------------------------===//
 /// String.prototype.
 
+/// 22.1.3.1
+CallResult<HermesValue>
+stringPrototypeAt(void *, Runtime &runtime, NativeArgs args) {
+  GCScope gcScope(runtime);
+  // 1. Let O be RequireObjectCoercible(this value).
+  if (LLVM_UNLIKELY(
+          checkObjectCoercible(runtime, args.getThisHandle()) ==
+          ExecutionStatus::EXCEPTION)) {
+    return ExecutionStatus::EXCEPTION;
+  }
+
+  // 2. Let S be ToString(O).
+  auto strRes = toString_RJS(runtime, args.getThisHandle());
+  if (LLVM_UNLIKELY(strRes == ExecutionStatus::EXCEPTION)) {
+    return ExecutionStatus::EXCEPTION;
+  }
+  auto S = runtime.makeHandle(std::move(*strRes));
+
+  // 3. Let len be the length of S.
+  double len = S->getStringLength();
+
+  // 4. Let relativeIndex be ? ToIntegerOrInfinity(index).
+  auto idx = args.getArgHandle(0);
+  auto relativeIndexRes = toIntegerOrInfinity(runtime, idx);
+  if (LLVM_UNLIKELY(relativeIndexRes == ExecutionStatus::EXCEPTION)) {
+    return ExecutionStatus::EXCEPTION;
+  }
+  const double relativeIndex = relativeIndexRes->getNumber();
+
+  double k;
+  // 5. If relativeIndex ≥ 0, then
+  if (relativeIndex >= 0) {
+    // a. Let k be relativeIndex.
+    k = relativeIndex;
+  } else {
+    // 6. Else,
+    // a. Let k be len + relativeIndex.
+    k = len + relativeIndex;
+  }
+
+  // 6. If k < 0 or k ≥ len, return undefined.
+  if (k < 0 || k >= len) {
+    return HermesValue::encodeUndefinedValue();
+  }
+
+  // 8. Return the substring of S from k to k + 1.
+  auto sliceRes = StringPrimitive::slice(runtime, S, k, 1);
+  if (LLVM_UNLIKELY(sliceRes == ExecutionStatus::EXCEPTION)) {
+    return ExecutionStatus::EXCEPTION;
+  }
+  return sliceRes;
+}
+
 CallResult<HermesValue>
 stringPrototypeToString(void *, Runtime &runtime, NativeArgs args) {
   if (args.getThisArg().isString()) {

lib/VM/JSLib/TypedArray.cpp

@@ -759,6 +759,68 @@ typedArrayPrototypeByteOffset(void *, Runtime &runtime, NativeArgs args) {
                                                         : 0);
 }
 
+/// ES6 23.2.3.1
+CallResult<HermesValue>
+typedArrayPrototypeAt(void *, Runtime &runtime, NativeArgs args) {
+  // 1. Let O be the this value.
+  // 2. Perform ? ValidateTypedArray(O).
+  if (LLVM_UNLIKELY(
+          JSTypedArrayBase::validateTypedArray(
+              runtime, args.getThisHandle(), true) ==
+          ExecutionStatus::EXCEPTION)) {
+    return ExecutionStatus::EXCEPTION;
+  }
+  GCScope gcScope{runtime};
+
+  auto O = args.vmcastThis<JSTypedArrayBase>();
+
+  // 3. Let len be O.[[ArrayLength]].
+  // The this object’s [[ArrayLength]] internal slot is accessed in place of
+  // performing a [[Get]] of "length".
+  double len = O->getLength();
+
+  // 4. Let relativeIndex be ? ToIntegerOrInfinity(index).
+  auto idx = args.getArgHandle(0);
+  auto relativeIndexRes = toIntegerOrInfinity(runtime, idx);
+  if (relativeIndexRes == ExecutionStatus::EXCEPTION) {
+    return ExecutionStatus::EXCEPTION;
+  }
+  const double relativeIndex = relativeIndexRes->getNumber();
+
+  double k;
+  // 5. If relativeIndex ≥ 0, then
+  if (relativeIndex >= 0) {
+    // a. Let k be relativeIndex.
+    k = relativeIndex;
+  } else {
+    // 6. Else,
+    // a. Let k be len + relativeIndex.
+    k = len + relativeIndex;
+  }
+
+  // 7. If k < 0 or k ≥ len, return undefined.
+  if (k < 0 || k >= len) {
+    return HermesValue::encodeUndefinedValue();
+  }
+
+  // 8. Return ? Get(O, ! ToString(𝔽(k))).
+  // Since we know we have a TypedArray, we can directly call JSTypedArray::at
+  // rather than getComputed_RJS like the spec mandates.
+#define TYPED_ARRAY(name, type)                                            \
+  case CellKind::name##ArrayKind: {                                        \
+    auto *arr = vmcast<JSTypedArray<type, CellKind::name##ArrayKind>>(*O); \
+    if (!arr->attached(runtime)) {                                         \
+      return runtime.raiseTypeError("Underlying ArrayBuffer detached");    \
+    }                                                                      \
+    return HermesValue::encodeNumberValue(arr->at(runtime, k));            \
+  }
+  switch (O->getKind()) {
+#include "hermes/VM/TypedArrays.def"
+    default:
+      llvm_unreachable("Invalid TypedArray after ValidateTypedArray call");
+  }
+}
+
 /// ES6 22.2.3.5
 CallResult<HermesValue>
 typedArrayPrototypeCopyWithin(void *, Runtime &runtime, NativeArgs args) {
@@ -1752,6 +1814,13 @@ Handle<JSObject> createTypedArrayBaseConstructor(Runtime &runtime) {
       false,
       true);
   // Methods.
+  defineMethod(
+      runtime,
+      proto,
+      Predefined::getSymbolID(Predefined::at),
+      nullptr,
+      typedArrayPrototypeAt,
+      1);
   defineMethod(
       runtime,
       proto,

test/hermes/TypedArray.js

@@ -443,6 +443,19 @@ cons.forEach(function(TypedArray) {
 });
 /// @}
 
+/// @name %TypedArray%.prototype.at
+/// @{
+cons.forEach(function(TA) {
+  var ta = new TA([1, 2, 3, 4, 5]);
+  assert.equal(ta.at(0).toString(), '1');
+  assert.equal(ta.at(-1).toString(), '5');
+  assert.equal(ta.at(10), undefined);
+  assert.throws(function(){TA.prototype.at.call(ta, 1n)}, TypeError);
+  assert.throws(function(){TA.prototype.at.call("hi", 1)}, TypeError);
+  assert.throws(function(){TA.prototype.at.call([1, "f", 3], 1)}, TypeError);
+});
+// @}
+
 /// @name %TypedArray%.prototype.copyWithin
 /// @{
 

test/hermes/array-functions.js

@@ -1099,3 +1099,24 @@ print(arrayEquals([1,2,3].flatMap(function(x) {
   return [x, x+this];
 }, 100), [1,101,2,102,3,103]));
 // CHECK-NEXT: true
+
+print([1, 2, 3, 4, 5].at(1));
+// CHECK-NEXT: 2
+print(Array.prototype.at.call({length: 3, 0: 'a', 1: 'b', 2: 'c'}, 1));
+// CHECK-NEXT: b
+print([1, 2, 3, 4, 5].at(6));
+// CHECK-NEXT: undefined
+print(Array.prototype.at.call({length: 0, 0: 'a', 1: 'b', 2: 'c'}, 1));
+// CHECK-NEXT: undefined
+try { [].at(1n); } catch(e) { print(e.name) }
+// CHECK-NEXT: TypeError
+print([1, 2, 3, 4, 5].at(-1));
+// CHECK-NEXT: 5
+print([1, 2, 3, 4, 5].at(-5));
+// CHECK-NEXT: 1
+print([1, 2, 3, 4, 5].at(-6));
+// CHECK-NEXT: undefined
+print(Array.prototype.at.call({length: 3, 0: 'a', 1: 'b', 2: 'c'}, -1));
+// CHECK-NEXT: c
+print(Array.prototype.at.call({length: 30}, 5));
+// CHECK-NEXT: undefined

test/hermes/string-functions.js

@@ -492,6 +492,20 @@ print('empty', res, res.length);
 print(String.prototype.trimEnd === String.prototype.trimRight);
 // CHECK-NEXT: true
 
+
+print('at');
+// CHECK-NEXT: at
+print("abc".at(1));
+// CHECK-NEXT: b
+print("abc".at(-1));
+// CHECK-NEXT: c
+print("abc".at(false));
+// CHECK-NEXT: a
+print(String.prototype.at.call(true, -1));
+// CHECK-NEXT: e
+print("".at(0));
+// CHECK-NEXT: undefined
+
 print('indexOf');
 // CHECK-LABEL: indexOf
 print('abc'.indexOf('a'))

utils/testsuite/testsuite_skiplist.py

@@ -432,10 +432,6 @@
     "test262/test/built-ins/Array/prototype/splice/create-ctor-non-object.js",
     "test262/test/built-ins/Array/prototype/flat/non-object-ctor-throws.js",
     "test262/test/built-ins/Array/prototype/flatMap/this-value-ctor-non-object.js",
-    # TODO(T76109235) proposal-relative-indexing-method
-    "test262/test/built-ins/Array/prototype/at/",
-    "test262/test/built-ins/TypedArray/prototype/at/",
-    "test262/test/built-ins/String/prototype/at/",
     # TODO(T90541287) array length coercion order
     "test262/test/built-ins/Array/length/define-own-prop-length-coercion-order-set.js",
     "test262/test/built-ins/Array/length/define-own-prop-length-coercion-order.js",