Link type names in RBS signatures to documentation pages

The JS highlighter resolves type names against the search index and
wraps matches in <a> tags. Qualified names like Foo::Bar::Baz are
collected as single linked units. Types not found in the index
remain as unlinked <span> elements.

Author: st0012

lib/rdoc/generator/template/aliki/js/rbs_highlighter.js

@@ -0,0 +1,116 @@
+/**
+ * Client-side RBS type signature highlighter for RDoc
+ *
+ * Highlights type names and built-in keywords in inline RBS annotations.
+ * Links type names to their documentation pages using the search index.
+ *
+ * NOTE: innerHTML usage is safe here — input is the element's own textContent
+ * (not user-supplied) and all output is escaped through escapeHtml(). This
+ * follows the same pattern as c_highlighter.js and bash_highlighter.js.
+ */
+
+(function() {
+  'use strict';
+
+  var BUILTIN_TYPES = new Set([
+    'void', 'untyped', 'nil', 'bool', 'self', 'top', 'bot',
+    'instance', 'class', 'true', 'false'
+  ]);
+
+  var typeLookup = null;
+
+  function buildTypeLookup() {
+    var lookup = {};
+    if (!window.search_data || !window.search_data.index) return lookup;
+
+    window.search_data.index.forEach(function(entry) {
+      if (entry.type === 'class' || entry.type === 'module') {
+        lookup[entry.full_name] = entry.path;
+        // Also map short name if not already taken
+        var short = entry.name;
+        if (!lookup[short]) lookup[short] = entry.path;
+      }
+    });
+    return lookup;
+  }
+
+  function escapeHtml(text) {
+    return text
+      .replace(/&/g, '&')
+      .replace(/</g, '&lt;')
+      .replace(/>/g, '&gt;');
+  }
+
+  function isIdentChar(ch) {
+    return (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') ||
+           (ch >= '0' && ch <= '9') || ch === '_';
+  }
+
+  function highlightRbs(text) {
+    var tokens = [];
+    var i = 0;
+    var len = text.length;
+    var prefix = typeof rdoc_rel_prefix !== 'undefined' ? rdoc_rel_prefix : '';
+
+    while (i < len) {
+      var ch = text[i];
+
+      // Uppercase identifier — possibly a type name, collect qualified name (Foo::Bar)
+      if (ch >= 'A' && ch <= 'Z') {
+        var end = i + 1;
+        while (end < len && isIdentChar(text[end])) end++;
+        // Collect :: continuations
+        while (end + 1 < len && text[end] === ':' && text[end + 1] === ':') {
+          end += 2;
+          while (end < len && isIdentChar(text[end])) end++;
+        }
+        var name = text.substring(i, end);
+        var href = typeLookup ? typeLookup[name] : null;
+
+        if (href) {
+          tokens.push('<a href="' + prefix + href + '" class="rbs-type">' + escapeHtml(name) + '</a>');
+        } else {
+          tokens.push('<span class="rbs-type">' + escapeHtml(name) + '</span>');
+        }
+        i = end;
+        continue;
+      }
+
+      // Lowercase identifier — check for builtin keywords
+      if ((ch >= 'a' && ch <= 'z') || ch === '_') {
+        var end = i + 1;
+        while (end < len && isIdentChar(text[end])) end++;
+        var word = text.substring(i, end);
+
+        if (BUILTIN_TYPES.has(word)) {
+          tokens.push('<span class="rbs-builtin">' + escapeHtml(word) + '</span>');
+        } else {
+          tokens.push(escapeHtml(word));
+        }
+        i = end;
+        continue;
+      }
+
+      tokens.push(escapeHtml(ch));
+      i++;
+    }
+
+    return tokens.join('');
+  }
+
+  function initHighlighting() {
+    typeLookup = buildTypeLookup();
+
+    document.querySelectorAll('.method-type-signature code').forEach(function(el) {
+      if (el.getAttribute('data-highlighted') === 'true') return;
+      el.innerHTML = highlightRbs(el.textContent); // eslint-disable-line no-unsanitized/property
+      el.setAttribute('data-highlighted', 'true');
+    });
+  }
+
+  if (document.readyState === 'loading') {
+    document.addEventListener('DOMContentLoaded', initHighlighting);
+  } else {
+    initHighlighting();
+  }
+})();