Add coverage for Object.assign with an array target (#4603)

test/built-ins/Object/assign/target-Array.js

@@ -0,0 +1,105 @@
+// Copyright 2015 Microsoft Corporation. All rights reserved.
+// This code is governed by the license found in the LICENSE file.
+
+/*---
+esid: sec-object.assign
+description: >
+  Object.assign with an Array Exotic Object target employs the corresponding
+  internal methods.
+info: |
+  Object.assign ( _target_, ..._sources_ )
+  3.a.iii.2.b. Perform ? Set(_to_, _nextKey_, _propValue_, *true*).
+
+  Set ( _O_, _P_, _V_, _Throw_ )
+  1. Let _success_ be ? _O_.[[Set]](_P_, _V_, _O_).
+
+  OrdinarySet ( _O_, _P_, _V_, _Receiver_ )
+  1. Let _ownDesc_ be ? _O_.[[GetOwnProperty]](_P_).
+  2. Return ? OrdinarySetWithOwnDescriptor(_O_, _P_, _V_, _Receiver_, _ownDesc_).
+
+  OrdinarySetWithOwnDescriptor ( _O_, _P_, _V_, _Receiver_, _ownDesc_ )
+  1. If _ownDesc_ is *undefined*, then
+     a. Let _parent_ be ? O.[[GetPrototypeOf]]().
+     b. If _parent_ is not *null*, then
+        i. Return ? _parent_.[[Set]](_P_, _V_, _Receiver_).
+     c. Else,
+        i. Set _ownDesc_ to the PropertyDescriptor { [[Value]]: *undefined*, [[Writable]]: *true*, [[Enumerable]]: *true*, [[Configurable]]: *true* }.
+  2. If IsDataDescriptor(_ownDesc_) is *true*, then
+     ...
+     c. Let _existingDescriptor_ be ? _Receiver_.[[GetOwnProperty]](_P_).
+     d. If _existingDescriptor_ is not *undefined*, then
+        ...
+        iii. Let _valueDesc_ be the PropertyDescriptor { [[Value]]: _V_ }.
+        iv. Return ? _Receiver_.[[DefineOwnProperty]](_P_, _valueDesc_).
+     e. Else,
+        i. Assert: _Receiver_ does not currently have a property _P_.
+        ii. Return ? CreateDataProperty(_Receiver_, _P_, _V_).
+
+  CreateDataProperty ( _O_, _P_, _V_ )
+  1. Let _newDesc_ be the PropertyDescriptor { [[Value]]: _V_, [[Writable]]: *true*, [[Enumerable]]: *true*, [[Configurable]]: *true* }.
+  2. Return ? _O_.[[DefineOwnProperty]](_P_, _newDesc_).
+
+  Array exotic object [[DefineOwnProperty]] ( _P_, _Desc_ )
+  1. If _P_ is *"length"*, then
+     a. Return ? ArraySetLength(_A_, _Desc_).
+  2. Else if _P_ is an array index, then
+     ...
+     k. If _index_ ≥ _length_, then
+        i. Set _lengthDesc_.[[Value]] to _index_ + *1*𝔽.
+        ii. Set _succeeded_ to ! OrdinaryDefineOwnProperty(_A_, *"length"*, _lengthDesc_).
+  3. Return ? OrdinaryDefineOwnProperty(_A_, _P_, _Desc_).
+
+  The Object Type
+  An **integer index** is a property name _n_ such that CanonicalNumericIndexString(_n_) returns an
+  integral Number in the inclusive interval from *+0*𝔽 to 𝔽(2**53 - 1). An **array index** is an
+  integer index _n_ such that CanonicalNumericIndexString(_n_) returns an integral Number in the
+  inclusive interval from *+0*𝔽 to 𝔽(2**32 - 2).
+---*/
+
+var target = [7, 8, 9];
+var result = Object.assign(target, [1]);
+assert.sameValue(result, target);
+assert.compareArray(result, [1, 8, 9],
+  "elements must be assigned from an array source onto an array target");
+
+var sparseArraySource = [];
+sparseArraySource[2] = 3;
+result = Object.assign(target, sparseArraySource);
+assert.sameValue(result, target);
+assert.compareArray(result, [1, 8, 3], "holes in a sparse array source must not be copied");
+
+var shortObjectSource = { 1: 2, length: 2 };
+shortObjectSource["-0"] = -1;
+shortObjectSource["1.5"] = -2;
+shortObjectSource["4294967295"] = -3; // 2**32 - 1
+result = Object.assign(target, shortObjectSource);
+assert.sameValue(result, target);
+assert.compareArray(result, [1, 2],
+  "array index properties must be copied from a non-array source");
+assert.sameValue(result["-0"], -1,
+  "a property with name -0 must be assigned onto an array target");
+assert.sameValue(result["1.5"], -2,
+  "a property with name 1.5 must be assigned onto an array target");
+assert.sameValue(result["4294967295"], -3,
+  "a property with name 4294967295 (2**32 - 1) must be assigned onto an array target");
+
+result = Object.assign(target, { length: 1 });
+assert.sameValue(result, target);
+assert.compareArray(result, [1], "assigning a short length must shrink an array target");
+
+result = Object.assign(target, { 2: 0 });
+assert.sameValue(result, target);
+assert.compareArray(result, [1, undefined, 0],
+  "assigning a high array index must grow an array target");
+
+if (typeof Proxy !== 'undefined') {
+  var accordionSource = new Proxy({ length: 0, 1: 9 }, {
+    ownKeys: function() {
+      return ["length", "1"];
+    }
+  });
+  result = Object.assign(target, accordionSource);
+  assert.sameValue(result, target);
+  assert.compareArray(result, [undefined, 9],
+    "assigning a short length before a high array index must shrink and then grow an array target");
+}