Expose XRSession's granted features (#1296)

alcooper91 · web-flow · commit a493dd5c1d68 · 2022-08-24T14:00:19.000-07:00
1. Exposes the XRSession's set of granted features as a FrozenArray attribute 'enabledFeatures'

2. Requires feature descriptors to be represented by DOMStrings, with any additional initialization being added as an extended member on XRSessionInit.

Note that this second change is consistent with how feature descriptors have currently been extended by the various other specs. It essentially requires that we have a string representation of the feature and can then further configure the feature as needed.
diff --git a/index.bs b/index.bs
@@ -512,8 +512,8 @@ Additionally, developers are encouraged to design experiences which progressivel
 
 <pre class="idl">
 dictionary XRSessionInit {
-  sequence&lt;any&gt; requiredFeatures;
-  sequence&lt;any&gt; optionalFeatures;
+  sequence&lt;DOMString&gt; requiredFeatures;
+  sequence&lt;DOMString&gt; optionalFeatures;
 };
 </pre>
 
@@ -523,13 +523,11 @@ The <dfn dict-member for="XRSessionInit">optionalFeatures</dfn> array contains a
 
 Values given in the feature lists are considered a valid <dfn>feature descriptor</dfn> if the value is one of the following:
 
- - Any {{XRReferenceSpaceType}} enum value
+ - The string representation of any {{XRReferenceSpaceType}} enum value
 
 Future iterations of this specification and additional modules may expand the list of accepted [=feature descriptors=].
 
-Note: Features are accepted as an array of {{any}} values to ensure forwards compatibility. It allows unrecognized optional values to be properly ignored as new [=feature descriptor=] types are added.
-
-Note: Features that can be stringified via <a abstract-op>ToString</a>() will be converted.
+Note: If a feature needs additional initialization, {{XRSessionInit}} should be extended with a new field for that feature.
 
 Depending on the {{XRSessionMode}} requested, certain [=feature descriptors=] are added to the {{XRSessionInit/requiredFeatures}} or {{XRSessionInit/optionalFeatures}} lists by default. The following table describes the <dfn>default features</dfn> associated with each session type and feature list:
 
@@ -621,6 +619,7 @@ enum XRVisibilityState {
   readonly attribute Float32Array? supportedFrameRates;
   [SameObject] readonly attribute XRRenderState renderState;
   [SameObject] readonly attribute XRInputSourceArray inputSources;
+  readonly attribute FrozenArray&lt;DOMString&gt; enabledFeatures;
 
   // Methods
   undefined updateRenderState(optional XRRenderStateInit state = {});
@@ -652,6 +651,8 @@ Each {{XRSession}} has an <dfn for=XRSession>animation frame</dfn>, which is an
 
 Each {{XRSession}} has a <dfn for=XRSession>set of granted features</dfn>, which is a [=/set=] of {{DOMString}}s corresponding to the [=feature descriptors=] that have been granted to the {{XRSession}}.
 
+The <dfn attribute for="XRSession">enabledFeatures</dfn> attribute returns the features in the [=XRSession/set of granted features=] as a new array of {{DOMString}}s.
+
 <div class="algorithm" data-algorithm="initialize-session">
 
 To <dfn>initialize the session</dfn>, given |session|, |mode|, |granted|, and |device|, the user agent MUST run the following steps:
@@ -2795,8 +2796,8 @@ The <dfn permission>"xr"</dfn> [=powerful feature=]’s permission-related algor
 <pre class="idl">
 dictionary XRPermissionDescriptor: PermissionDescriptor {
   XRSessionMode mode;
-  sequence&lt;any&gt; requiredFeatures;
-  sequence&lt;any&gt; optionalFeatures;
+  sequence&lt;DOMString&gt; requiredFeatures;
+  sequence&lt;DOMString&gt; optionalFeatures;
 };
 </pre>
 
@@ -2810,7 +2811,7 @@ dictionary XRPermissionDescriptor: PermissionDescriptor {
 <pre class=idl>
 [Exposed=Window]
 interface XRPermissionStatus: PermissionStatus {
-  attribute FrozenArray&lt;any&gt; granted;
+  attribute FrozenArray&lt;DOMString&gt; granted;
 };
 </pre>
 
@@ -2887,21 +2888,15 @@ To <dfn>resolve the requested features</dfn> given |requiredFeatures| and |optio
   1. Add every [=feature descriptor=] in the [=default features=] table associated with |mode| to |granted| if it is not already present.
   1. For each |feature| in |requiredFeatures| perform the following steps:
     1. If the |feature| is `null`, [=continue=] to the next entry.
-    1. If |feature| is not a valid [=feature descriptor=], perform the following steps:
-        1. Let |s| be the result of calling [=?=] <a abstract-op>ToString</a>(|feature|).
-        1. If |s| is not a valid [=feature descriptor=] or is `undefined`, return `null`.
-        1. Set |feature| to |s|.
+    1. If |feature| is not a valid [=feature descriptor=], return `null`.
     1. If |feature| is already in |granted|, continue to the next entry.
     1. If the requesting document's [=origin=] is not allowed to use any [[#permissions-policy|permissions policy]] required by |feature| as indicated by the [=feature requirements=] table, return `null`.
     1. If |session|'s [=XRSession/XR device=] is not [=capable of supporting=] the functionality described by |feature| or the user agent has otherwise determined to reject the feature, return `null`.
     1. If the functionality described by |feature| requires [=explicit consent=] and |feature| is not in |previouslyEnabled|, append it to |consentRequired|.
     1. Else append |feature| to |granted|.
   1. For each |feature| in |optionalFeatures| perform the following steps:
     1. If the |feature| is `null`, [=continue=] to the next entry.
-    1. If |feature| is not a valid [=feature descriptor=], perform the following steps:
-        1. Let |s| be the result of calling [=?=] <a abstract-op>ToString</a>(|feature|).
-        1. If |s| is not a valid [=feature descriptor=] or is `undefined`, [=continue=] to the next entry.
-        1. Set |feature| to |s|.
+    1. If |feature| is not a valid [=feature descriptor=], [=continue=] to the next entry.
     1. If |feature| is already in |granted|, continue to the next entry.
     1. If the requesting document's origin is not allowed to use any [[#permissions-policy|permissions policy]] required by |feature| as indicated by the [=feature requirements=] table, continue to the next entry.
     1. If |session|'s [=XRSession/XR device=] is not [=capable of supporting=] the functionality described by |feature| or the user agent has otherwise determined to reject the feature, continue to the next entry.
