1 files changed, 86 insertions, 0 deletions
diff --git a/js/src/tests/ecma_6/Function/configurable-length.js b/js/src/tests/ecma_6/Function/configurable-length.js
new file mode 100644
index 000000000..127038fb5
--- /dev/null
+++ b/js/src/tests/ecma_6/Function/configurable-length.js
@@ -0,0 +1,86 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/ */
+
+// Very simple initial test that the "length" property of a function is
+// configurable. More thorough tests follow.
+var f = function (a1, a2, a3, a4) {};
+assertEq(delete f.length, true);
+assertEq(f.hasOwnProperty("length"), false);
+assertEq(f.length, 0);  // inherited from Function.prototype.length
+assertEq(delete Function.prototype.length, true);
+assertEq(f.length, undefined);
+
+
+// Now for the details.
+//
+// Many of these tests are poking at the "resolve hook" mechanism SM uses to
+// lazily create this property, which is wonky and deserving of some extra
+// skepticism.
+
+// We've deleted Function.prototype.length. Check that the resolve hook does
+// not resurrect it.
+assertEq("length" in Function.prototype, false);
+Function.prototype.length = 7;
+assertEq(Function.prototype.length, 7);
+delete Function.prototype.length;
+assertEq(Function.prototype.length, undefined);
+
+// OK, define Function.prototype.length back to its original state per spec, so
+// the remaining tests can run in a more typical environment.
+Object.defineProperty(Function.prototype, "length", {value: 0, configurable: true});
+
+// Check the property descriptor of a function length property.
+var g = function f(a1, a2, a3, a4, a5) {};
+var desc = Object.getOwnPropertyDescriptor(g, "length");
+assertEq(desc.configurable, true);
+assertEq(desc.enumerable, false);
+assertEq(desc.writable, false);
+assertEq(desc.value, 5);
+
+// After deleting the length property, assigning to f.length fails because
+// Function.prototype.length is non-writable. In strict mode it would throw.
+delete g.length;
+g.length = 12;
+assertEq(g.hasOwnProperty("length"), false);
+assertEq(g.length, 0);
+
+// After deleting both the length property and Function.prototype.length,
+// assigning to f.length creates a new plain old data property.
+delete Function.prototype.length;
+g.length = 13;
+var desc = Object.getOwnPropertyDescriptor(g, "length");
+assertEq(desc.configurable, true);
+assertEq(desc.enumerable, true);
+assertEq(desc.writable, true);
+assertEq(desc.value, 13);
+
+// Deleting the .length of one instance of a FunctionDeclaration does not
+// affect other instances.
+function mkfun() {
+    function fun(a1, a2, a3, a4, a5) {}
+    return fun;
+}
+g = mkfun();
+var h = mkfun();
+delete h.length;
+assertEq(g.length, 5);
+assertEq(mkfun().length, 5);
+
+// Object.defineProperty on a brand-new function is sufficient to cause the
+// LENGTH_RESOLVED flag to be set.
+g = mkfun();
+Object.defineProperty(g, "length", {value: 0});
+assertEq(delete g.length, true);
+assertEq(g.hasOwnProperty("length"), false);
+
+// Object.defineProperty on a brand-new function correctly merges new
+// attributes with the builtin ones.
+g = mkfun();
+Object.defineProperty(g, "length", { value: 42 });
+desc = Object.getOwnPropertyDescriptor(g, "length");
+assertEq(desc.configurable, true);
+assertEq(desc.enumerable, false);
+assertEq(desc.writable, false);
+assertEq(desc.value, 42);
+
+reportCompare(0, 0, 'ok');