Add collapsible styles for C++ docs

pytorch_sphinx_theme2/static/js/collapsible-list.js

@@ -0,0 +1,54 @@
+/**
+ * Collapsible "Subclassed by" list behavior.
+ * Finds paragraphs starting with "Subclassed by" that have more than 5 items,
+ * collapses them to a single line, and adds a "See All" / "Hide" toggle button.
+ *
+ * Breathe/Doxygen renders "Subclassed by" in a <p> tag. The subclass names may
+ * be <a> links (when targets exist) or plain text (when they don't). We count
+ * both to determine whether to collapse.
+ */
+document.addEventListener('DOMContentLoaded', function() {
+    var paragraphs = document.querySelectorAll('p');
+
+    paragraphs.forEach(function(p) {
+        var text = p.textContent.trim();
+        if (!text.startsWith('Subclassed by')) return;
+
+        // Count items: use <a> links if present, otherwise count comma-separated entries
+        var links = p.querySelectorAll('a');
+        var itemCount = links.length;
+        if (itemCount <= 5) {
+            // Links may not exist (plain text subclass names). Count comma-separated items.
+            var afterLabel = text.replace(/^Subclassed by\s*/, '');
+            var commaCount = afterLabel.split(',').filter(function(s) { return s.trim().length > 0; }).length;
+            if (commaCount > itemCount) {
+                itemCount = commaCount;
+            }
+        }
+
+        if (itemCount > 5) {
+            p.classList.add('subclassed-by-list', 'collapsed');
+
+            var toggle = document.createElement('button');
+            toggle.className = 'subclassed-by-toggle';
+            toggle.textContent = 'See All (' + itemCount + ')';
+            toggle.type = 'button';
+
+            toggle.addEventListener('click', function(e) {
+                e.preventDefault();
+
+                if (p.classList.contains('collapsed')) {
+                    p.classList.remove('collapsed');
+                    p.classList.add('expanded');
+                    toggle.textContent = 'Hide';
+                } else {
+                    p.classList.remove('expanded');
+                    p.classList.add('collapsed');
+                    toggle.textContent = 'See All (' + itemCount + ')';
+                }
+            });
+
+            p.appendChild(toggle);
+        }
+    });
+});

pytorch_sphinx_theme2/static/scss/_collapsible_list.scss

@@ -0,0 +1,60 @@
+/*
+ * Collapsible "Subclassed by" list styles.
+ * When a paragraph has more than 5 links, it collapses to a single line
+ * with a "See All" button to expand the full list.
+ * Main use case is C++ docs
+ */
+
+/* Container for the subclassed-by list */
+.subclassed-by-list {
+    position: relative;
+
+    /* Initially collapsed state - show only 1 line */
+    &.collapsed {
+        max-height: 1.6em;
+        overflow: hidden;
+        white-space: nowrap;
+        text-overflow: ellipsis;
+        padding-right: 140px; /* Space for the button */
+    }
+
+    /* Expanded state */
+    &.expanded {
+        max-height: none;
+        overflow: visible;
+        white-space: normal;
+        padding-right: 0;
+        padding-bottom: 2em; /* Space for the button at the bottom */
+
+        .subclassed-by-toggle {
+            position: absolute;
+            top: auto;
+            bottom: 0;
+            right: 0;
+        }
+    }
+}
+
+/* The "See All" / "Hide" toggle button */
+.subclassed-by-toggle {
+    position: absolute;
+    top: 0;
+    right: 0;
+    background-color: #f0f0f0;
+    border: 1px solid #ccc;
+    border-radius: 4px;
+    padding: 2px 10px;
+    color: #333;
+    cursor: pointer;
+    font-size: 0.85em;
+    text-decoration: none;
+    font-family: inherit;
+    font-weight: 500;
+    transition: background-color 0.2s, border-color 0.2s;
+
+    &:hover {
+        background-color: #e0e0e0;
+        border-color: #999;
+        text-decoration: none;
+    }
+}

pytorch_sphinx_theme2/static/scss/main.scss

@@ -15,6 +15,7 @@
 @use 'search';
 @use 'tippy';
 @use 'navbar_dropdown';
+@use 'collapsible_list';
 
 // Import FontAwesome
 @use "@fortawesome/fontawesome-free/scss/fontawesome";

pytorch_sphinx_theme2/templates/layout.html

@@ -208,11 +208,24 @@
         link.parentElement.classList.remove('active');
       });
 
-      // Add active class to the matching link
+      // Add active class to the matching link and all its ancestor TOC items
       const matchingLink = tocNav.querySelector(`a[href="#${CSS.escape(targetId)}"]`);
       if (matchingLink) {
         matchingLink.classList.add('active');
         matchingLink.parentElement.classList.add('active');
+
+        // Walk up the DOM to activate parent TOC entries (e.g. h2 parent of h3)
+        let ancestor = matchingLink.parentElement.parentElement;
+        while (ancestor && ancestor !== tocNav) {
+          if (ancestor.classList.contains('toc-entry')) {
+            ancestor.classList.add('active');
+            const parentLink = ancestor.querySelector(':scope > a.nav-link');
+            if (parentLink) {
+              parentLink.classList.add('active');
+            }
+          }
+          ancestor = ancestor.parentElement;
+        }
       }
 
       // Use setTimeout to reset the guard after the current call stack