Modify $262.uncallableAndIsHTMLDDA() to $262.IsHTMLDDA (#1305)

Modify $262.uncallableAndIsHTMLDDA() to an optional $262.IsHTMLDDA (whose use must be guarded by a feature of the same name), and narrowly/correctly prescribe its requirements consistent with `document.all`'s behavior in HTML. 

INTERPRETING.md

@@ -64,16 +64,16 @@ properties of the global scope prior to test execution.
         6. Return Completion(status).
 
   - **`global`** - a reference to the global object on which `$262` was initially defined
-  - **`uncallableAndIsHTMLDDA`** - a function that returns an object *`obj`* for
-    which [Call](https://tc39.github.io/ecma262/#sec-call)(*`obj`*, *any value*, «»)
-    throws a `TypeError`.  (The value of [IsCallable]()(*`obj`*) is unspecified:
-    a callable *`obj`* that throws a `TypeError` or an uncallable *`obj`* works
-    equally well.)  In hosts supporting the
-    [IsHTMLDDA](https://tc39.github.io/ecma262/#sec-IsHTMLDDA-internal-slot)
-    internal slot, *`obj`* must also have such a slot.  (These highly specific
-    behaviors are entirely motivated by the very few tests that use this.  Read
-    them for an explanation.)  Tests that use this function should be marked as
-    using the `uncallableAndIsHTMLDDA` feature.
+  - **`IsHTMLDDA`** - (present only in implementations that can provide it) an
+    object that 1) has an [[IsHTMLDDA]] internal slot, and 2) when called with
+    no arguments or with the single argument `""` returns `null`.  Use this
+    property to test that ECMAScript algorithms aren't mis-implemented to treat
+    `document.all` as being `undefined` or of type Undefined (instead of
+    Object).  (The peculiar second requirement permits testing algorithms when
+    they also call `document.all` with such arguments, so that testing for
+    correct behavior requires knowing how the call behaves.  This is rarely
+    necessary.)  Tests using this function must be tagged with the `IsHTMLDDA`
+    feature so that only hosts supporting this property will run them.
   - **`agent`** - an ordinary object with the following properties:
     - **`start`** - a function that takes a script source string and runs
       the script in a concurrent agent.  Will block until that agent is

features.txt

@@ -124,4 +124,4 @@ WeakSet
 # language features, exposed through global-environment functions on the $262
 # object, go here.
 
-uncallableAndIsHTMLDDA
+IsHTMLDDA

test/annexB/language/expressions/yield/star-iterable-return-emulates-undefined-throws-when-called.js

@@ -2,18 +2,19 @@
 // This code is governed by the BSD license found in the LICENSE file.
 
 /*---
-es6id: sec-generator-function-definitions-runtime-semantics-evaluation
+esid: sec-generator-function-definitions-runtime-semantics-evaluation
 description: >
     If <iterator>.return is an object emulating `undefined` (e.g. `document.all`
     in browsers), it shouldn't be treated as if it were actually `undefined` by
     the yield* operator.
-features: [generators, uncallableAndIsHTMLDDA]
+features: [generators, IsHTMLDDA]
 ---*/
 
+var IsHTMLDDA = $262.IsHTMLDDA;
 var iter = {
   [Symbol.iterator]() { return this; },
   next() { return {}; },
-  return: $262.uncallableAndIsHTMLDDA(),
+  return: IsHTMLDDA,
 };
 
 var outer = (function*() { yield* iter; })();
@@ -21,11 +22,10 @@ var outer = (function*() { yield* iter; })();
 outer.next();
 
 assert.throws(TypeError, function() {
-  // This code is expected to throw a TypeError because `iter.return` throws a
-  // TypeError when invoked with `iter` as `this` and no arguments provided.
-  // It's irrelevant that in hosts that support the [[IsHTMLDDA]] internal slot,
-  // this object has that slot: `<iterator>.return` behavior is skipped only if
-  // that property is exactly the value `undefined`, not a value loosely equal
-  // to it.
-  outer.return();
+  // `IsHTMLDDA` is called here with `iter` as `this` and `emptyString` as the
+  // sole argument, and it's specified to return `null` under these conditions.
+  // As `iter`'s iteration isn't ending because of a throw, the iteration
+  // protocol will then throw a `TypeError` because `null` isn't an object.
+  var emptyString = "";
+  outer.return(emptyString);
 });

test/annexB/language/statements/for-await-of/iterator-close-return-emulates-undefined-throws-when-called.js

@@ -7,19 +7,23 @@ description: >
     `GetIterator(obj, ~async~)` must attempt to call `obj[@@asyncIterator]` when
     that value is an object with an [[IsHTMLDDA]] internal slot, not act as if
     the value were `undefined`.
-features: [async-iteration, uncallableAndIsHTMLDDA]
+features: [async-iteration, IsHTMLDDA]
 flags: [async]
 ---*/
 
 async function f() {
-  var fakeIter = {
-    [Symbol.asyncIterator]: $262.uncallableAndIsHTMLDDA(),
+  var IsHTMLDDA = $262.IsHTMLDDA;
+  var iter = {
+    [Symbol.asyncIterator]: IsHTMLDDA,
     get [Symbol.iterator]() {
       throw new Test262Error("shouldn't touch Symbol.iterator");
     },
   };
 
-  for await (var x of fakeIter)
+  // `IsHTMLDDA` is called here with `iter` as `this` and no arguments, and it's
+  // expected to return `null` under these conditions.  Then the iteration
+  // protocol throws a `TypeError` because `null` isn't an object.
+  for await (var x of iter)
     return "for-await-of body shouldn't be reached";
 
   return "should have failed earlier";
@@ -28,7 +32,8 @@ async function f() {
 f().then($DONE,
          function (e) {
            assert.sameValue(e.constructor, TypeError,
-                            "expected TypeError from calling " +
-                            "uncallableAndIsHTMLDDA() value: " + e);
+                            "expected TypeError because " +
+                            "`iter[Symbol.asyncIterator]() returned a " +
+                            "non-object: " + e);
          })
    .then($DONE, $DONE);

test/annexB/language/statements/for-of/iterator-close-return-emulates-undefined-throws-when-called.js

@@ -2,26 +2,24 @@
 // This code is governed by the BSD license found in the LICENSE file.
 
 /*---
-es6id: sec-iteratorclose
+esid: sec-iteratorclose
 description: >
     If <iterator>.return is an object emulating `undefined` (e.g. `document.all`
     in browsers), it shouldn't be treated as if it were actually `undefined`.
-features: [generators, uncallableAndIsHTMLDDA]
+features: [generators, IsHTMLDDA]
 ---*/
 
+var IsHTMLDDA = $262.IsHTMLDDA;
 var iter = {
   [Symbol.iterator]() { return this; },
   next() { return {}; },
-  return: $262.uncallableAndIsHTMLDDA(),
+  return: IsHTMLDDA,
 };
 
 assert.throws(TypeError, function() {
-  // This code is expected to throw a TypeError because `iter.return` throws a
-  // TypeError when invoked with `iter` as `this` and no arguments provided.
-  // It's irrelevant that in hosts that support the [[IsHTMLDDA]] internal slot,
-  // this object has that slot: `<iterator>.return` behavior is skipped only if
-  // that property is exactly the value `undefined`, not a value loosely equal
-  // to it.
+  // `IsHTMLDDA` is called here with `iter` as `this` and no arguments, and it's
+  // specified to return `null` under these conditions.  Then the iteration
+  // protocol throws a `TypeError` because `null` isn't an object.
   for (var x of iter)
     break;
 });