Prevent infinite loop in revealing algorithms

josepharhar · web-flow · commit 55baf054d2c7 · 2025-08-01T12:52:41.000+02:00
The ancestor details revealing algorithm and the hidden until found revealing algorithm may both get stuck in infinite loops because they iterate the flat tree while firing synchronous events. If the page were to listen to these events and change the flat tree in response, then the algorithm could theoretically never end. Fixes #11436.
diff --git a/source b/source
@@ -61902,35 +61902,6 @@ interface <dfn interface>HTMLDetailsElement</dfn> : <span>HTMLElement</span> {
 
   </div>
 
-  <p>The <dfn>ancestor details revealing algorithm</dfn> is to run the following steps on
-  <var>currentNode</var>:</p>
-
-  <ol>
-   <li>
-    <p>While <var>currentNode</var> has a parent node within the <span>flat tree</span>:</p>
-
-    <ol>
-     <li>
-      <p>If <var>currentNode</var> is slotted into the second slot of a <code>details</code>
-      element:</p>
-
-      <ol>
-       <li><p>Set <var>currentNode</var> to the <code>details</code> element which
-       <var>currentNode</var> is slotted into.</p></li>
-
-       <li><p>If the <code data-x="attr-details-open">open</code> attribute is not set on
-       <var>currentNode</var>, then <span data-x="concept-element-attributes-set-value">set</span>
-       the <code data-x="attr-details-open">open</code> attribute on <var>currentNode</var> to the
-       empty string.</p></li>
-      </ol>
-     </li>
-
-     <li><p>Otherwise, set <var>currentNode</var> to the parent node of
-     <var>currentNode</var> within the <span>flat tree</span>.</p></li>
-    </ol>
-   </li>
-  </ol>
-
   <div class="example">
 
    <p>The following example shows the <code>details</code> element being used to hide technical
@@ -80071,8 +80042,7 @@ END:VCARD</pre>
   data-x="navigate-fragid">fragment navigation</span>. When these features attempt to scroll to a
   target which is in the element's subtree, the user agent will remove the <code
   data-x="attr-hidden">hidden</code> attribute in order to reveal the content before scrolling to
-  it by running the <span>ancestor hidden-until-found revealing algorithm</span> on the target
-  node.</p>
+  it by running the <span>ancestor revealing algorithm</span> on the target node.</p>
 
   <div w-nodev>
 
@@ -80227,30 +80197,80 @@ END:VCARD</pre>
    string.</p></li>
   </ol>
 
-  <p>The <dfn>ancestor hidden-until-found revealing algorithm</dfn> is to run the following steps on
-  <var>currentNode</var>:</p>
+  <p>An <dfn>ancestor reveal pair</dfn> is a <span>tuple</span> consisting of a <dfn
+  data-x="ancestor-reveal-pair-node">node</dfn> and a <dfn
+  data-x="ancestor-reveal-pair-string">string</dfn>.</p>
+
+  <p>The <dfn>ancestor revealing algorithm</dfn> given a node <var>target</var> is:</p>
 
   <ol>
+   <li><p>Let <var>ancestorsToReveal</var> be « ».</p></li>
+
+   <li><p>Let <var>ancestor</var> be <var>target</var>.</p></li>
+
+   <li>
+    <p>While <var>ancestor</var> has a parent node within the <span>flat tree</span>:</p>
+
+    <ol>
+     <li><p>If <var>ancestor</var> has a <code data-x="attr-hidden">hidden</code> attribute in the
+     <span data-x="attr-hidden-until-found-state">Hidden Until Found</span> state, then <span
+     data-x="list append">append</span> (<var>ancestor</var>, "<code data-x="">until-found</code>")
+     to <var>ancestorsToReveal</var>.</p></li>
+
+     <li><p>If <var>ancestor</var> is slotted into the second slot of a <code>details</code>
+     element which does not have an <code data-x="attr-details-open">open</code> attribute, then
+     <span data-x="list append">append</span> (<var>ancestor</var>'s parent node, "<code
+     data-x="">details</code>") to <var>ancestorsToReveal</var>.</p></li>
+
+     <li><p>Set <var>ancestor</var> to the parent node of <var>ancestor</var> within the
+     <span>flat tree</span>.</p></li>
+    </ol>
+   </li>
+
    <li>
-    <p>While <var>currentNode</var> has a parent node within the <span>flat tree</span>:</p>
+    <p>For each (<var>ancestorToReveal</var>, <var>revealType</var>) of
+    <var>ancestorsToReveal</var>:</p>
 
     <ol>
+     <li><p>If <var>ancestorToReveal</var> is not <span>connected</span>, then return.</p></li>
+
      <li>
-      <p>If <var>currentNode</var> has the <code data-x="attr-hidden">hidden</code> attribute in the
-      <span data-x="attr-hidden-until-found-state">Hidden Until Found</span> state, then:</p>
+      <p>If <var>revealType</var> is "<code data-x="">until-found</code>":</p>
 
       <ol>
+       <li><p>If <var>ancestorToReveal</var>'s <code data-x="attr-hidden">hidden</code> attribute is
+       not in the <span data-x="attr-hidden-until-found-state">Hidden Until Found</span> state, then
+       return.</p></li>
+
        <li><p><span data-x="concept-event-fire">Fire an event</span> named <code
-       data-x="event-beforematch">beforematch</code> at <var>currentNode</var> with the <code
+       data-x="event-beforematch">beforematch</code> at <var>ancestorToReveal</var> with the <code
        data-x="dom-Event-bubbles">bubbles</code> attribute initialized to true.</p></li>
 
+       <li><p>If <var>ancestorToReveal</var> is not <span>connected</span>, then return.</p></li>
+
+       <li><p>If <var>ancestorToReveal</var>'s <code data-x="attr-hidden">hidden</code> attribute is
+       not in the <span data-x="attr-hidden-until-found-state">Hidden Until Found</span> state, then
+       return.</p></li>
+
        <li><p>Remove the <code data-x="attr-hidden">hidden</code> attribute from
-       <var>currentNode</var>.</p></li>
+       <var>ancestorToReveal</var>.</p></li>
       </ol>
-     </li>
+     <li>
 
-     <li><p>Set <var>currentNode</var> to the parent node of <var>currentNode</var> within the
-     <span>flat tree</span>.</p></li>
+     <li>
+      <p>Otherwise:</p>
+
+      <ol>
+       <li><p><span>Assert</span>: <var>revealType</var> is "<code
+       data-x="">details</code>".</p></li>
+
+       <li><p>If <var>ancestorToReveal</var> has an <code data-x="attr-details-open">open</code>
+       attribute, then return.</p></li>
+
+       <li><p>Set <var>ancestorToReveal</var>'s <code data-x="attr-details-open">open</code>
+       attribute to the empty string.</p></li>
+      </ol>
+     </li>
     </ol>
    </li>
   </ol>
@@ -84122,15 +84142,8 @@ body { display:none }
    match</span>.</p></li>
 
    <li><p><span>Queue a global task</span> on the <span>user interaction task source</span> given
-   <var>node</var>'s <span>relevant global object</span> to run the following steps:</p>
-
-    <ol>
-     <li><p>Run the <span>ancestor details revealing algorithm</span> on <var>node</var>.</p></li>
-
-     <li><p>Run the <span>ancestor hidden-until-found revealing algorithm</span> on
-     <var>node</var>.</p></li>
-    </ol>
-   </li>
+   <var>node</var>'s <span>relevant global object</span> to run the <span>ancestor revealing
+   algorithm</span> on <var>node</var>.</p></li>
   </ol>
 
   <p class="warning">
@@ -106399,10 +106412,7 @@ location.href = '#foo';</code></pre>
 
      <li><p>Set <var>document</var>'s <span>target element</span> to <var>target</var>.</p></li>
 
-     <li><p>Run the <span>ancestor details revealing algorithm</span> on <var>target</var>.</p></li>
-
-     <li><p>Run the <span>ancestor hidden-until-found revealing algorithm</span> on
-     <var>target</var>.</p></li>
+     <li><p>Run the <span>ancestor revealing algorithm</span> on <var>target</var>.</p></li>
 
      <li><p><span data-x="scroll a target into view">Scroll <var>target</var> into view</span>,
      with <i>behavior</i> set to "auto", <i>block</i> set to "start", and <i>inline</i>
