Bug 860965 - Part 2: Add Array.build. (r=nmatsakis)

js/src/builtin/Array.js

@@ -1281,13 +1281,27 @@ function ArrayFilterPar(func, mode) {
 }
 
 /**
- * "Comprehension form": This is the function invoked for |Array.buildPar(len,
- * fn)| It creates a new array with length |len| where index |i| is equal to
- * |fn(i)|.
+ * "Comprehension form": This is the function invoked for
+ * |Array.{build,buildPar}(len, fn)| It creates a new array with length |len|
+ * where index |i| is equal to |fn(i)|.
  *
  * The final |mode| argument is an internal argument used only during our
  * unit-testing.
  */
+function ArrayStaticBuild(length, func) {
+  if (!IS_UINT32(length))
+    ThrowError(JSMSG_BAD_ARRAY_LENGTH);
+  if (!IsCallable(func))
+    ThrowError(JSMSG_NOT_FUNCTION, DecompileArg(1, func));
+
+  var buffer = NewDenseArray(length);
+
+  for (var i = 0; i < length; i++)
+    UnsafePutElements(buffer, i, func(i));
+
+  return buffer;
+}
+
 function ArrayStaticBuildPar(length, func, mode) {
   if (!IS_UINT32(length))
     ThrowError(JSMSG_BAD_ARRAY_LENGTH);

js/src/jit-test/tests/collections/Array-build-basic.js

@@ -0,0 +1,20 @@
+// Array.build basics
+
+load(libdir + "asserts.js");
+load(libdir + "eqArrayHelper.js");
+
+function myBuild(l, f) {
+  var a = [];
+  for (var i = 0; i < l; i++)
+    a.push(f(i));
+  return a;
+}
+
+// Test that build returns an identical, but new array.
+var a1 = [];
+for (var i = 0; i < 100; i++)
+  a1[i] = Math.random();
+var a2 = Array.build(a1.length, (i) => a1[i]);
+
+assertEq(a1 === a2, false);
+assertEqArray(a2, a1);

js/src/jit-test/tests/collections/Array-build-surfaces.js

@@ -0,0 +1,21 @@
+// Check superficial features of Array.build.
+
+load(libdir + "asserts.js");
+
+var desc = Object.getOwnPropertyDescriptor(Array, "build");
+assertEq(desc.configurable, true);
+assertEq(desc.enumerable, false);
+assertEq(desc.writable, true);
+assertEq(Array.build.length, 2);
+assertThrowsInstanceOf(() => new Array.build(), TypeError);  // not a constructor
+
+// Must pass a function to second argument.
+for (let v of [undefined, null, false, "cow"])
+  assertThrowsInstanceOf(() => Array.build(1, v), TypeError);
+
+// The first argument must be a legal length.
+assertThrowsInstanceOf(() => Array.build(-1, function() {}), RangeError);
+
+// When the this-value passed in is not a constructor, the result is an array.
+for (let v of [undefined, null, false, "cow"])
+  assertEq(Array.isArray(Array.build.call(v, 1, function() {})), true);

js/src/jsarray.cpp

@@ -2833,6 +2833,7 @@ static const JSFunctionSpec array_static_methods[] = {
          {"some",               {NULL, NULL},       2,0, "ArrayStaticSome"},
          {"reduce",             {NULL, NULL},       2,0, "ArrayStaticReduce"},
          {"reduceRight",        {NULL, NULL},       2,0, "ArrayStaticReduceRight"},
+         {"build",              {NULL, NULL},       2,0, "ArrayStaticBuild"},
     JS_FN("of",                 array_of,           0,0),
 
 #ifdef ENABLE_PARALLEL_JS