Specify open dictionaries.

index.bs

@@ -106,6 +106,10 @@ urlPrefix: https://tc39.github.io/ecma262/; spec: ECMA-262
         text: Set; url: sec-set-o-p-v-throw
         text: IsConstructor; url: sec-isconstructor
         text: Construct; url: sec-construct
+        text: own property; url: sec-own-property
+        text: enumerable; url: sec-property-attributes
+        text: HasOwnProperty; url: sec-hasownproperty
+        text: EnumerableOwnProperties; url: sec-enumerableownproperties
         text: DefinePropertyOrThrow; url: sec-definepropertyorthrow
         url: sec-code-realms
             text: Realm
@@ -120,6 +124,7 @@ urlPrefix: https://tc39.github.io/ecma262/; spec: ECMA-262
         text: ECMA-262 section 9.1.8; url: sec-ordinary-object-internal-methods-and-internal-slots-get-p-receiver
         text: ECMA-262 section 19.2.2.3; url: sec-function-@@create
         text: ECMA-262 section 19.2.3.8; url: sec-function.prototype-@@hasinstance
+        text: List; url: sec-list-and-record-specification-type
         text: Array methods; url: sec-properties-of-the-array-prototype-object
         text: typed arrays; url: sec-typedarray-objects
         text: GetMethod; url: sec-getmethod
@@ -1358,8 +1363,10 @@ The type of the attribute, after resolving typedefs, must not be a
 
 *   a [=sequence type=]
 *   a [=dictionary type=]
+*   an [=open dictionary type=]
 *   a [=union type=]
-    that has a nullable or non-nullable sequence type or dictionary
+    that has a nullable or non-nullable sequence type, dictionary,
+    or open dictionary
     as one of its [=flattened member types=]
 
 The attribute is <dfn id="dfn-read-only" export>read only</dfn> if the
@@ -1750,15 +1757,15 @@ corresponding argument omitted.
     conversion of <emu-val>undefined</emu-val> to be used (i.e., <emu-val>false</emu-val>).
 </p>
 
-If the type of an argument is a [=dictionary type=]
+If the type of an argument is a [=dictionary type=] or [=open dictionary type=]
 or a [=union type=] that has a
-dictionary type as one of its [=flattened member types=],
+dictionary or open dictionary type as one of its [=flattened member types=],
 and that dictionary type and its ancestors have no [=required dictionary member|required members=],
 and the argument is either the final argument or is followed only by
 [=optional arguments=], then
 the argument must be specified as optional.
 Such arguments are always considered to have a
-[=optional argument/default value=] of an empty dictionary,
+[=optional argument/default value=] of an empty dictionary or open dictionary, as appropriate,
 unless otherwise specified.
 
 <div class="note">
@@ -3249,7 +3256,6 @@ extended attribute’s [=takes a named argument list|named argument list=].
 
 Two types are <dfn id="dfn-distinguishable" export>distinguishable</dfn> if
 at most one of the two [=includes a nullable type=]
-or is a [=dictionary type=],
 and at least one of the following three conditions is true:
 
 1.  The two types (taking their [=inner types=]
@@ -3280,7 +3286,7 @@ and at least one of the following three conditions is true:
                     <span>callback function</span>
             </div></th>
                 <th><div>
-                    <span>dictionary</span>
+                    <span>[open] dictionary</span>
             </div></th>
                 <th><div>
                     <span>sequence&lt;|T|&gt;</span>
@@ -3389,7 +3395,7 @@ and at least one of the following three conditions is true:
             <td>●</td>
         </tr>
         <tr>
-            <th>dictionary</th>
+            <th>[open] dictionary</th>
             <td class="belowdiagonal"></td>
             <td class="belowdiagonal"></td>
             <td class="belowdiagonal"></td>
@@ -5171,6 +5177,7 @@ type.
         "DOMException" Null
         BufferRelatedType Null
         "FrozenArray" "&lt;" Type "&gt;" Null
+        OpenDictionaryType Null
 </pre>
 
 <div data-fill-with="grammar-ConstType"></div>
@@ -5219,6 +5226,17 @@ type.
         "Promise" "&lt;" ReturnType "&gt;"
 </pre>
 
+<pre class="grammar" id="prod-OpenDictionaryType">
+    OpenDictionaryType :
+        "OpenDictionary" "&lt;" Type OpenDictionaryTypeMaybeValue
+</pre>
+
+<pre class="grammar" id="prod-OpenDictionaryTypeMaybeValue">
+    OpenDictionaryTypeMaybeValue :
+        "&gt;"
+        "," Type "&gt;"
+</pre>
+
 <pre class="grammar" id="prod-Null">
     Null :
         "?"
@@ -5664,10 +5682,11 @@ character after an existing type.  The inner type must not
 be {{any}},
 another nullable type, or a [=union type=]
 that itself has [=includes a nullable type=]
-or has a dictionary type as one of its
+or has a dictionary or open dictionary type as one of its
 [=flattened member types=].
 
-Note: Although dictionary types can in general be nullable, they cannot when used
+Note: Although dictionary and open dictionary types can in general be nullable,
+they cannot when used
 as the type of an operation argument or a dictionary member.
 
 Nullable type constant values in IDL are represented in the same way that
@@ -5737,6 +5756,35 @@ is the concatenation of the type name for |T| and
 the string “Sequence”.
 
 
+<h4 id="idl-open-dictionary" dictionary lt="OpenDictionary">Open dictionary types — OpenDictionary&lt;[|K|,] |V|&gt;</h4>
+
+An <dfn export>open dictionary type</dfn> is a parameterized type
+whose values are ordered associative arrays mapping instances of |K| to
+instances of |V|. The (key, value) pairs are called
+<dfn for="OpenDictionary">mappings</dfn>.
+The order of an open dictionary's mappings is determined when the open
+dictionary value is created.
+
+|K| must be one of {{DOMString}}, {{USVString}}, or {{ByteString}}. In a type
+name of the form <code>OpenDictionary&lt;|V|></code>, which omits |K|, |K| defaults
+to {{DOMString}}.
+
+Open dictionaries are always passed by value. In language bindings where an open
+dictionary is represented by an object of some kind, passing an open dictionary
+to a [=platform object=] will not result in a reference to the open dictionary
+being kept by that object. Similarly, any open dictionary returned from a
+platform object will be a copy and modifications made to it will not be visible
+to the platform object.
+
+There is no way to represent a constant open dictionary value in IDL.
+
+Open dictionaries must not be used as the type of an [=attribute=] or
+[=constant=].
+
+The [=type name=] of an open dictionary type is the concatenation of the type
+name for |K|, the type name for |V| and the string “OpenDictionary”.
+
+
 <h4 oldids="dom-promise" id="idl-promise" interface lt="Promise|Promise&lt;T&gt;">Promise types — Promise&lt;|T|&gt;</h4>
 
 A <dfn id="dfn-promise-type" export>promise type</dfn> is a parameterized type
@@ -5833,7 +5881,7 @@ be used as a [=member types|union member type=].
 The [=number of nullable member types=]
 of a [=union type=] must
 be 0 or 1, and if it is 1 then the union type must also not have
-a [=dictionary type=] in its
+a [=dictionary type=] or [=open dictionary type=] in its
 [=flattened member types=].
 
 A type <dfn id="dfn-includes-a-nullable-type" export>includes a nullable type</dfn> if:
@@ -7529,6 +7577,95 @@ iterable |iterable| and an iterator getter
 </div>
 
 
+<h4 id="es-open-dictionary">Open dictionaries — OpenDictionary&lt;[|K|,] |V|&gt;</h4>
+
+IDL {{OpenDictionary}}&lt;|K|, |V|&gt; values are represented by
+ECMAScript <emu-val>Object</emu-val> values.
+
+<p id="es-to-open-dictionary">
+    An ECMAScript value |O| is [=converted to an IDL value|converted=] to an IDL <code>{{OpenDictionary}}<|K|, |V|></code> value as follows:
+</p>
+
+<ol class="algorithm">
+    1.  Let |result| be a new empty instance of <code>{{OpenDictionary}}<|K|, |V|></code>.
+    1.  If [=Type=](|O|) is <emu-val>Undefined</emu-val> or <emu-val>Null</emu-val>,
+        return |result|.
+    1.  If [=Type=](|O|) is not <emu-val>Object</emu-val>,
+        <a lt="es throw">throw a <emu-val>TypeError</emu-val></a>.
+    1.  Let |keys| be [=?=] [=EnumerableOwnProperties=](|O|, "key").
+    1.  Repeat, for each element |key| of |keys| in [=List=] order:
+        1.  If [=!=] [=HasOwnProperty=](|O|, |key|) is <code>true</code>, then:
+            1.  Let |typedKey| be |key| [=converted to an IDL value=] of type |K|.
+            1.  Let |value| be [=?=] [=Get=](|O|, |key|).
+            1.  Let |typedValue| be |value| [=converted to an IDL value=] of type |V|.
+            1.  Assert: |typedKey| is not yet a key in |result|.
+            1.  Append to |result| a mapping from |typedKey| to |typedValue|.
+    1.  Return |result|.
+</ol>
+
+<p id="open-dictionary-to-es">
+    An IDL <code>{{OpenDictionary}}<…></code> value |D| is [=converted to an
+    ECMAScript value|converted=] to an ECMAScript value as follows:
+</p>
+
+<ol class="algorithm">
+    1.  Let |result| be [=!=] [=ObjectCreate=]([=%ObjectPrototype%=]).
+    1.  Repeat, for each [=OpenDictionary/mapping=] (|key|, |value|) in |D|:
+        1.  Let |esKey| be |key| [=converted to an ECMAScript value=].
+        1.  Let |esValue| be |value| [=converted to an ECMAScript value=].
+        1.  Let |created| be [=!=] [=CreateDataProperty=](|result|, |esKey|, |esValue|).
+        1.  Assert: |created| is <code>true</code>.
+    1.  Return |result|.
+</ol>
+
+<div class="example" id="example-es-open-dictionary">
+    Passing the ECMAScript value <code>{b: 3, a: 4}</code> to a
+    <code>{{OpenDictionary}}&lt;DOMString, double></code> argument
+    would result in the IDL value <code>[ ("b", 3), ("a", 4) ]</code>.
+
+    Open dictionaries only consider [=own property|own=] [=enumerable=] properties, so given an IDL operation
+    <code>OpenDictionary&lt;double> identity(OpenDictionary&lt;double> arg)</code> which
+    returns its argument, the following code passes its assertions:
+
+    <pre highlight="js">
+        let proto = {a: 3, b: 4};
+        let obj = {__proto__: proto, d: 5, c: 6}
+        Object.defineProperty(obj, "e", {value: 7, enumerable: false});
+        let result = identity(obj);
+        console.assert(result.a === undefined);
+        console.assert(result.b === undefined);
+        console.assert(result.e === undefined);
+        let entries = Object.entries(result);
+        console.assert(entries[0][0] === "d");
+        console.assert(entries[0][1] === 5);
+        console.assert(entries[1][0] === "c");
+        console.assert(entries[1][1] === 6);
+    </pre>
+
+    Open dictionary keys and values can be constrained, although keys can only be
+    constrained among the three string types.
+    The following conversions have the described results:
+    <table class="data">
+        <thead><th>Value</th><th>Passed to type</th><th>Result</th></thead>
+        <tr>
+            <td><code>{"😞": 1}</code></td>
+            <td><code>{{OpenDictionary}}&lt;ByteString, double></code></td>
+            <td><emu-val>TypeError</emu-val></td>
+        </tr>
+        <tr>
+            <td><code>{"\uD83D": 1}</code></td>
+            <td><code>{{OpenDictionary}}&lt;USVString, double></code></td>
+            <td>[ ("\uFFFD", 1) ]</td>
+        </tr>
+        <tr>
+            <td><code>{"\uD83D": {hello: "world"}}</code></td>
+            <td><code>{{OpenDictionary}}&lt;DOMString, double></code></td>
+            <td>[ ("\uD83D", 0) ]</td>
+        </tr>
+    </table>
+</div>
+
+
 <h4 id="es-promise">Promise types — Promise&lt;|T|&gt;</h4>
 
 IDL [=promise type=] values are
@@ -7695,6 +7832,9 @@ represented by ECMAScript values that correspond to the union’s
         1.  If |types| includes a [=dictionary type=], then return the
             result of [=converted to an IDL value|converting=]
             |V| to that dictionary type.
+        1.  If |types| includes an [=open dictionary type=], then return the
+            result of [=converted to an IDL value|converting=]
+            |V| to that dictionary type.
         1.  If |types| includes a [=callback interface=]
             type, then return the result of
             [=converted to an IDL value|converting=]
@@ -9843,6 +9983,7 @@ and a list of IDL values or the special value “missing”.  The algorithm beha
             and there is an entry in |S| that has one of the following types at position |i| of its type list,
             *   a [=nullable type=]
             *   a [=dictionary type=]
+            *   an [=open dictionary type=]
             *   a [=union type=] that
                 [=includes a nullable type=] or that
                 has a [=dictionary type=] in its [=flattened member types|flattened members=]
@@ -9955,6 +10096,7 @@ and a list of IDL values or the special value “missing”.  The algorithm beha
             there is an entry in |S| that has one of the following types at position |i| of its type list,
             *   a [=callback interface=] type
             *   a [=dictionary type=]
+            *   an [=open dictionary type=]
             *   {{object}}
             *   a [=nullable type|nullable=] version of any of the above types
             *   a [=union type=] or [=nullable type|nullable=] union type