Add [AllowShared] to allow accepting SharedArrayBuffers

Previous to this commit, any API that accepted any of the buffer source types would also accept a SharedArrayBuffer. This was not the approach we want; instead, we want APIs to explicitly opt-in. Enabled by previous work creating annotated types, this adds the new [AllowShared] extended attribute to allow APIs to opt in to accepting SharedArrayBuffers.

While here, this removes an unimplemented check for detached array buffers when converting from ES values to IDL types, fixing #352.

Author: domenic

index.bs

@@ -41,6 +41,10 @@ urlPrefix: http://www.unicode.org/glossary/; spec: UNICODE
     type: dfn
         text: Unicode scalar value; url: unicode_scalar_value
 urlPrefix: https://tc39.github.io/ecma262/; spec: ECMA-262
+    type: interface; for: ECMAScript
+        text: ArrayBuffer; url: sec-arraybuffer-objects
+        text: DataView; url: sec-dataview-objects
+        text: SharedArrayBuffer; url: sec-sharedarraybuffer-objects
     type: dfn
         text: NumericLiteral; url: sec-literals-numeric-literals
         text: ECMAScript error objects; url: sec-error-objects
@@ -110,6 +114,7 @@ urlPrefix: https://tc39.github.io/ecma262/; spec: ECMA-262
         text: CreateDataProperty; url: sec-createdataproperty
         text: DetachArrayBuffer; url: sec-detacharraybuffer
         text: IsDetachedBuffer; url: sec-isdetachedbuffer
+        text: IsSharedArrayBuffer; url: sec-issharedarraybuffer
         text: SetIntegrityLevel; url: sec-setintegritylevel
         url: sec-array-iterator-objects
             text: array iterator object
@@ -7799,34 +7804,44 @@ ECMAScript <emu-val>Object</emu-val> values.
 <h4 id="es-buffer-source-types">Buffer source types</h4>
 
 Values of the IDL [=buffer source types=]
-are represented by objects of the corresponding ECMAScript class.
+are represented by objects of the corresponding ECMAScript class, with the additional restriction
+that unless the type is [=extended attributes associated with|associated with=] the
+[{{AllowShared}}] extended attribute, they can only be backed by ECMAScript
+{{ECMAScript/ArrayBuffer}} objects, and not {{ECMAScript/SharedArrayBuffer}} objects.
 
-<div id="es-to-buffer-source" algorithm="convert an ECMAScript value to buffer source">
+<div id="es-to-buffer-source" algorithm="convert an ECMAScript value to IDL ArrayBuffer">
 
     An ECMAScript value |V| is [=converted to an IDL value|converted=]
     to an IDL {{ArrayBuffer}} value by running the following algorithm:
 
     1.  If [=Type=](|V|) is not Object,
         or |V| does not have an \[[ArrayBufferData]] [=internal slot=],
-        or [=IsDetachedBuffer=](|V|) is true,
         then [=ECMAScript/throw=] a <emu-val>TypeError</emu-val>.
+    1.  If the conversion is not to an IDL type
+        [=extended attributes associated with|associated with=] the [{{AllowShared}}]
+        [=extended attribute=], and [=IsSharedArrayBuffer=](|V|) is true, then [=ECMAScript/throw=]
+        a <emu-val>TypeError</emu-val>.
     1.  Return the IDL {{ArrayBuffer}} value that is a reference
         to the same object as |V|.
 </div>
 
-<div id="buffer-source-to-es" algorithm="convert a buffer source to an ECMAScript value">
+<div id="buffer-source-to-es" algorithm="convert an ECMAScript value to IDL DataView">
 
     An ECMAScript value |V| is [=converted to an IDL value|converted=]
     to an IDL {{DataView}} value by running the following algorithm:
 
     1.  If [=Type=](|V|) is not Object,
         or |V| does not have a \[[DataView]] [=internal slot=],
         then [=ECMAScript/throw=] a <emu-val>TypeError</emu-val>.
+    1.  If the conversion is not to an IDL type
+        [=extended attributes associated with|associated with=] the [{{AllowShared}}]
+        [=extended attribute=], and [=IsSharedArrayBuffer=](|V|.\[[ViewedArrayBuffer]]) is true,
+        then [=ECMAScript/throw=] a <emu-val>TypeError</emu-val>.
     1.  Return the IDL {{DataView}} value that is a reference
         to the same object as |V|.
 </div>
 
-<div algorithm="convert an ECMAScript value to buffer source type">
+<div algorithm="convert an ECMAScript value to IDL typed array">
 
     An ECMAScript value |V| is
     [=converted to an IDL value|converted=]
@@ -7842,9 +7857,15 @@ are represented by objects of the corresponding ECMAScript class.
     by running the following algorithm:
 
     1.  Let |T| be the IDL type |V| is being converted to.
+    1.  Let |typedArrayName| be the [=type name|name=] of |T|'s [=annotated types/inner type=] if
+        |T| is an [=annotated type=], or the [=type name|name=] of |T| otherwise.
     1.  If [=Type=](|V|) is not Object,
         or |V| does not have a \[[TypedArrayName]] [=internal slot=]
-        with a value equal to the name of |T|,
+        with a value equal to |typedArrayName|,
+        then [=ECMAScript/throw=] a <emu-val>TypeError</emu-val>.
+    1.  If the conversion is not to an IDL type
+        [=extended attributes associated with|associated with=] the [{{AllowShared}}]
+        [=extended attribute=], and [=IsSharedArrayBuffer=](|V|.\[[ViewedArrayBuffer]]) is true,
         then [=ECMAScript/throw=] a <emu-val>TypeError</emu-val>.
     1.  Return the IDL value of type |T| that is a reference to the same object as |V|.
 </div>
@@ -7858,7 +7879,7 @@ a reference to the same object that the IDL value represents.
 
     When [=get a reference to the buffer source|getting a reference to=]
     or [=get a copy of the buffer source|getting a copy of the bytes held by a buffer source=]
-    that is an ECMAScript <emu-val>ArrayBuffer</emu-val>, <emu-val>DataView</emu-val>
+    that is an ECMAScript {{ECMAScript/ArrayBuffer}}, {{ECMAScript/DataView}}
     or typed array object, these steps must be followed:
 
     1.  Let |O| be the ECMAScript object that is the buffer source.
@@ -7945,6 +7966,38 @@ This section defines a number of
 whose presence affects only the ECMAScript binding.
 
 
+<h4 id="AllowShared" extended-attribute lt="AllowShared">[AllowShared]</h4>
+
+If the [{{AllowShared}}] [=extended attribute=] appears on one of the [=buffer source types=], it
+creates a new IDL type that allows the buffer source type to be backed by an ECMAScript
+{{ECMAScript/SharedArrayBuffer}}, instead of only by a non-shared {{ECMAScript/ArrayBuffer}}.
+
+The [{{AllowShared}}] extended attribute must [=takes no arguments|take no arguments=].
+
+A type that is not a [=buffer source type=] must not be
+[=extended attributes associated with|associated with=] the [{{AllowShared}}] extended attribute.
+
+See the rules for converting ECMAScript values to IDL [=buffer source types=] in
+[[#es-buffer-source-types]] for the specific requirements that the use of [{{AllowShared}}] entails.
+
+<div class="example">
+    In the following [=IDL fragment=], one operation's argument uses the [{{AllowShared}}] extended
+    attribute, while the other does not:
+
+    <pre highlight="webidl">
+        interface RenderingContext {
+          void readPixels(long width, long height, BufferSource pixels);
+          void readPixelsShared(long width, long height, [AllowShared] BufferSource pixels);
+        };
+    </pre>
+
+    With this definition, a call to <code>readPixels</code> with an {{ECMAScript/SharedArrayBuffer}}
+    instance, or any typed array or {{ECMAScript/DataView}} backed by one, will throw a
+    {{TypeError}} exception. In contrast, a call to <code>readPixelsShared</code> will allow such
+    objects as input.
+</div>
+
+
 <h4 id="Clamp" extended-attribute lt="Clamp">[Clamp]</h4>
 
 If the [{{Clamp}}] [=extended attribute=] appears on one of the [=integer types=], it creates a new
@@ -7962,7 +8015,7 @@ attribute. A type must not be [=extended attributes associated with|associated w
 not be [=extended attributes associated with|associated with=] the [{{Clamp}}] extended attribute.
 
 See the rules for converting ECMAScript values to the various IDL integer
-types in [[#es-type-mapping]]
+types in [[#es-integer-types]]
 for the specific requirements that the use of
 [{{Clamp}}] entails.
 
@@ -7981,7 +8034,7 @@ for the specific requirements that the use of
         };
     </pre>
 
-    In an ECMAScript implementation of the IDL, a call to setColorClamped with
+    A call to <code>setColorClamped</code> with
     <emu-val>Number</emu-val> values that are out of range for an
     {{octet}} are clamped to the range [0, 255].