Simplify the reentrance guard for custom element definition

domenic · annevk · commit 4bfa7130c7e2 · 2016-08-20T07:15:29.000+02:00
Previously, we would allow reentrance as long as it was not with the same name or constructor as was currently being defined, using the mechanism of a "set of being-defined names" and "set of being-defined constructors". This was overly complex, given that there are not really any use cases for defining a custom element in a getter triggered by the element definition algorithm. So instead, we move to just using an overall reentrance-guard flag. Fixes WICG/webcomponents#545.
diff --git a/source b/source
@@ -66355,12 +66355,9 @@ dictionary <dfn>ElementDefinitionOptions</dfn> {
   data-x="concept-custom-element-definition-local-name">local name</span>, or <span
   data-x="concept-custom-element-definition-constructor">constructor</span>.</p>
 
-  <p>Every <code>CustomElementsRegistry</code> also has a <dfn>set of being-defined names</dfn> and
-  a <dfn>set of being-defined constructors</dfn>, containing <span data-x="valid custom element
-  name">valid custom element names</span> and JavaScript function objects, respectively. These are
-  used to ensure that when script executes during <span>element definition</span>, which can
-  reentrantly cause <span>element definition</span> again, the script cannot define another element
-  using the same name or constructor.</p>
+  <p>Every <code>CustomElementsRegistry</code> also has an <dfn>element definition is running</dfn>
+  flag which is used to prevent reentrant invocations of <span>element definition</span>. It is
+  initially unset.</p>
 
   <p>Every <code>CustomElementsRegistry</code> also has a <dfn>when-defined promise map</dfn>,
   mapping <span data-x="valid custom element name">valid custom element names</span> to promises. It
@@ -66448,20 +66445,11 @@ dictionary <dfn>ElementDefinitionOptions</dfn> {
    <span>"<code>NotSupportedError</code>"</span> <code>DOMException</code> and abort these
    steps.</p></li>
 
-   <li><p>If this <code>CustomElementsRegistry</code>'s <span>set of being-defined names</span>
-   contains <var>name</var>, then throw a <span>"<code>NotSupportedError</code>"</span>
-   <code>DOMException</code> and abort these steps.</p></li>
-
    <li><p>If this <code>CustomElementsRegistry</code> contains an entry with <span
    data-x="concept-custom-element-definition-constructor">constructor</span> <var>constructor</var>,
    then throw a <span>"<code>NotSupportedError</code>"</span> <code>DOMException</code> and abort
    these steps.</p></li>
 
-   <li><p>If this <code>CustomElementsRegistry</code>'s <span>set of being-defined
-   constructors</span> contains <var>constructor</var>, then throw a
-   <span>"<code>NotSupportedError</code>"</span> <code>DOMException</code> and abort these
-   steps.</p></li>
-
    <li><p>Let <var>localName</var> be <var>name</var>.</p></li>
 
    <li><p>Let <var>extends</var> be the value of the <code data-x="">extends</code> member of
@@ -66483,11 +66471,12 @@ dictionary <dfn>ElementDefinitionOptions</dfn> {
     </ol>
    </li>
 
-   <li><p>Add <var>name</var> to this <code>CustomElementsRegistry</code>'s <span>set of
-   being-defined names</span>.</p></li>
+   <li><p>If this <code>CustomElementsRegistry</code>'s <span>element definition is running</span>
+   flag is set, then throw a <span>"<code>NotSupportedError</code>"</span> <code>DOMException</code>
+   and abort these steps.</p></li>
 
-   <li><p>Add <var>constructor</var> to this <code>CustomElementsRegistry</code>'s <span>set of
-   being-defined constructors</span>.</p></li>
+   <li><p>Set this <code>CustomElementsRegistry</code>'s <span>element definition is running</span>
+   flag.</p></li>
 
    <li>
     <p>Run the following substeps while catching any exceptions:</p>
@@ -66540,18 +66529,15 @@ dictionary <dfn>ElementDefinitionOptions</dfn> {
       </ol>
     </ol>
 
-    <p>Then, perform the following substeps, regardless of whether the above steps threw an
-    exception or not:</p>
+    <p>Then, perform the following substep, regardless of whether the above steps threw an exception
+    or not:</p>
 
     <ol>
-     <li><p>Remove <var>name</var> from this <code>CustomElementsRegistry</code>'s <span>set of
-     being-defined names</span>.</p></li>
-
-     <li><p>Remove <var>constructor</var> from this <code>CustomElementsRegistry</code>'s <span>set
-     of being-defined constructors</span>.</p></li>
+     <li><p>Unset this <code>CustomElementsRegistry</code>'s <span>element definition is
+     running</span> flag.</p></li>
     </ol>
 
-    <p>Finally, if the first set of steps threw an exception, then rethrow that exception, and
+    <p>Finally, if the first set of substeps threw an exception, then rethrow that exception, and
     terminate this algorithm. Otherwise, continue onward.</p>
    </li>
 
