Support ES2019 Array.prototype.flat (#1313)

* feat: implement Array.prototype.flat

* tests: add (slightly modified) harmony test

* feat: throw TypeError if array is too big

* fix: remove constructor assigned Array.flat

* fix: just remove the comment about es2019

By other code looks like the Rhino version context is just ES6.

* tests: update test262

---------

Co-authored-by: RBRi <rbri@rbri.de>

src/org/mozilla/javascript/NativeArray.java

@@ -291,6 +291,10 @@ protected void initPrototypeId(int id) {
                 arity = 2;
                 s = "copyWithin";
                 break;
+            case Id_flat:
+                arity = 0;
+                s = "flat";
+                break;
             default:
                 throw new IllegalArgumentException(String.valueOf(id));
         }
@@ -427,6 +431,9 @@ public Object execIdCall(
                 case Id_copyWithin:
                     return js_copyWithin(cx, scope, thisObj, args);
 
+                case Id_flat:
+                    return js_flat(cx, scope, thisObj, args);
+
                 case Id_every:
                 case Id_filter:
                 case Id_forEach:
@@ -1000,6 +1007,14 @@ private static void defineElem(Context cx, Scriptable target, long index, Object
         }
     }
 
+    private static void defineElemOrThrow(Context cx, Scriptable target, long index, Object value) {
+        if (index > NativeNumber.MAX_SAFE_INTEGER) {
+            throw ScriptRuntime.typeErrorById("msg.arraylength.too.big", String.valueOf(index));
+        } else {
+            defineElem(cx, target, index, value);
+        }
+    }
+
     private static void setElem(Context cx, Scriptable target, long index, Object value) {
         if (index > Integer.MAX_VALUE) {
             String id = Long.toString(index);
@@ -1959,6 +1974,44 @@ private static Object js_copyWithin(
         return thisObj;
     }
 
+    private static Object js_flat(Context cx, Scriptable scope, Scriptable thisObj, Object[] args) {
+        Scriptable o = ScriptRuntime.toObject(cx, scope, thisObj);
+        double depth;
+        if (args.length < 1 || Undefined.isUndefined(args[0])) {
+            depth = 1;
+        } else {
+            depth = ScriptRuntime.toInteger(args[0]);
+        }
+
+        return flat(cx, scope, o, depth);
+    }
+
+    private static Scriptable flat(Context cx, Scriptable scope, Scriptable source, double depth) {
+        long length = getLengthProperty(cx, source);
+
+        Scriptable result;
+        result = cx.newArray(scope, 0);
+        long j = 0;
+        for (long i = 0; i < length; i++) {
+            Object elem = getRawElem(source, i);
+            if (elem == Scriptable.NOT_FOUND) {
+                continue;
+            }
+            if (depth >= 1 && js_isArray(elem)) {
+                Scriptable arr = flat(cx, scope, (Scriptable) elem, depth - 1);
+                long arrLength = getLengthProperty(cx, arr);
+                for (long k = 0; k < arrLength; k++) {
+                    Object temp = getRawElem(arr, k);
+                    defineElemOrThrow(cx, result, j++, temp);
+                }
+            } else {
+                defineElemOrThrow(cx, result, j++, elem);
+            }
+        }
+        setLengthProperty(cx, result, j);
+        return result;
+    }
+
     /** Implements the methods "every", "filter", "forEach", "map", and "some". */
     private static Object iterativeMethod(
             Context cx,
@@ -2538,6 +2591,9 @@ protected int findPrototypeId(String s) {
             case "copyWithin":
                 id = Id_copyWithin;
                 break;
+            case "flat":
+                id = Id_flat;
+                break;
             default:
                 id = 0;
                 break;
@@ -2576,7 +2632,8 @@ protected int findPrototypeId(String s) {
             Id_entries = 29,
             Id_includes = 30,
             Id_copyWithin = 31,
-            SymbolId_iterator = 32,
+            Id_flat = 32,
+            SymbolId_iterator = 33,
             MAX_PROTOTYPE_ID = SymbolId_iterator;
     private static final int ConstructorId_join = -Id_join,
             ConstructorId_reverse = -Id_reverse,

testsrc/jstests/harmony/array-flat.js

@@ -0,0 +1,71 @@
+// 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.
+//
+// Taken from https://github.com/v8/v8/blob/main/test/mjsunit/harmony/array-flat.js and changed due to Rhino errors
+// TypeError: redeclaration of const input
+load("testsrc/assert.js");
+
+assertEquals(Array.prototype.flat.length, 0);
+assertEquals(Array.prototype.flat.name, 'flat');
+
+let input;
+
+{
+  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);
+}
+
+{
+  input = { 0: 'a', 1: 'b', 2: 'c', length: 'wat' };
+  assertEquals(Array.prototype.flat.call(input, Infinity), []);
+}
+
+{
+  let count = 0;
+  input = {
+    get length() { ++count; return 0; }
+  };
+  const result = Array.prototype.flat.call(input, Infinity);
+  assertEquals(count, 1);
+}
+
+{
+  const descriptor = Object.getOwnPropertyDescriptor(
+    Array.prototype,
+    'flat'
+  );
+  assertEquals(descriptor.value, Array.prototype.flat);
+  assertEquals(descriptor.writable, true);
+  assertEquals(descriptor.enumerable, false);
+  assertEquals(descriptor.configurable, true);
+}
+
+"success";

testsrc/org/mozilla/javascript/tests/Test262SuiteTest.java

@@ -89,7 +89,6 @@ public class Test262SuiteTest {
             new HashSet<>(
                     Arrays.asList(
                             "Array.prototype.flatMap",
-                            "Array.prototype.flat",
                             "Atomics",
                             "IsHTMLDDA",
                             "Proxy",

testsrc/org/mozilla/javascript/tests/harmony/ArrayFlatTest.java

@@ -0,0 +1,14 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.javascript.tests.harmony;
+
+import org.mozilla.javascript.Context;
+import org.mozilla.javascript.drivers.LanguageVersion;
+import org.mozilla.javascript.drivers.RhinoTest;
+import org.mozilla.javascript.drivers.ScriptTestsBase;
+
+@RhinoTest("testsrc/jstests/harmony/array-flat.js")
+@LanguageVersion(Context.VERSION_ES6)
+public class ArrayFlatTest extends ScriptTestsBase {}

testsrc/test262.properties

@@ -73,7 +73,18 @@ built-ins/Array 200/2670 (7.49%)
     prototype/findIndex/predicate-call-this-strict.js strict
     prototype/find/predicate-call-this-strict.js strict
     prototype/flatMap 21/21 (100.0%)
-    prototype/flat 17/17 (100.0%)
+    prototype/flat/array-like-objects.js
+    prototype/flat/bound-function-call.js
+    prototype/flat/empty-array-elements.js
+    prototype/flat/empty-object-elements.js
+    prototype/flat/non-numeric-depth-should-not-throw.js
+    prototype/flat/non-object-ctor-throws.js
+    prototype/flat/null-undefined-elements.js
+    prototype/flat/positive-infinity.js
+    prototype/flat/proxy-access-count.js
+    prototype/flat/target-array-non-extensible.js {unsupported: [Symbol.species]}
+    prototype/flat/target-array-with-non-configurable-property.js {unsupported: [Symbol.species]}
+    prototype/flat/target-array-with-non-writable-property.js {unsupported: [Symbol.species]}
     prototype/forEach/15.4.4.18-5-1-s.js non-strict
     prototype/includes/get-prop.js {unsupported: [Proxy]}
     prototype/indexOf/calls-only-has-on-prototype-after-length-zeroed.js {unsupported: [Proxy]}
@@ -155,7 +166,7 @@ built-ins/Array 200/2670 (7.49%)
     prototype/toLocaleString/primitive_this_value.js strict
     prototype/toLocaleString/primitive_this_value_getter.js strict
     prototype/unshift/throws-with-string-receiver.js
-    prototype/methods-called-as-functions.js {unsupported: [Symbol.species, Array.prototype.flat, Array.prototype.flatMap]}
+    prototype/methods-called-as-functions.js {unsupported: [Symbol.species, Array.prototype.flatMap]}
     prototype/Symbol.iterator.js Expects a particular string value
     Symbol.species 4/4 (100.0%)
     proto-from-ctor-realm-one.js {unsupported: [Reflect]}