fix: inlineTokens rebuilds the reflink-mask preamble per call

src/Lexer.ts

@@ -306,11 +306,11 @@ export class _Lexer<ParserOutput = string, RendererOutput = string> {
     let maskedSrc = src;
 
     // Mask out reflinks
-    if (this.tokens.links) {
-      const links = Object.keys(this.tokens.links);
-      if (links.length > 0) {
+    if (this.tokens.links && src.includes('[')) {
+      const links = new Set(Object.keys(this.tokens.links));
+      if (links.size > 0) {
         maskedSrc = maskedSrc.replace(this.tokenizer.rules.inline.reflinkSearch, match0 =>
-          links.includes(match0.slice(match0.lastIndexOf('[') + 1, -1))
+          links.has(match0.slice(match0.lastIndexOf('[') + 1, -1))
             ? '[' + 'a'.repeat(match0.length - 2) + ']'
             : match0);
       }

test/unit/inlineTokens-masking.test.js

@@ -0,0 +1,49 @@
+import { marked } from '../../lib/marked.esm.js';
+import { describe, it } from 'node:test';
+import assert from 'node:assert';
+
+/**
+ * Regression: many reference definitions + references must not be quadratic.
+ *
+ * Lexer.inlineTokens rebuilt its reflink-masking preamble (Object.keys over
+ * every link definition, then a reflinkSearch replace) on *every* call —
+ * including recursive link-text calls whose text cannot contain a reflink.
+ * With n defs and n refs that is O(n²) allocation churn (measured exponent
+ * ~3: 24s at n=13000). The fix skips the masking block when the source has
+ * no '[' (reflinkSearch cannot match without one) and uses a Set lookup.
+ */
+function footnoteShape(n) {
+  let refs = '';
+  const defs = [];
+  for (let i = 0; i < n; i++) {
+    refs += `[^${i}] `;
+    defs.push(`[^${i}]: x`);
+  }
+  return refs + '\n\n' + defs.join('\n');
+}
+
+function parseSeconds(text) {
+  marked.parse('warmup');
+  const t0 = process.hrtime.bigint();
+  marked.parse(text);
+  return Number(process.hrtime.bigint() - t0) / 1e9;
+}
+
+describe('inlineTokens masking scaling', () => {
+  it('stays near-linear over a doubling ladder', () => {
+    const t1 = parseSeconds(footnoteShape(2000));
+    const t2 = parseSeconds(footnoteShape(4000));
+    // pre-fix this ratio is ~5+ (exponent > 2); linear growth is ~2.
+    assert.ok(
+      t2 < Math.max(t1 * 3.5, 0.5),
+      `superlinear growth suspected: ${t1.toFixed(3)}s -> ${t2.toFixed(3)}s`,
+    );
+  });
+
+  it('renders reference links identically to the unmasked path', () => {
+    assert.strictEqual(
+      marked.parse('[a][b]\n\n[b]: /url "t"'),
+      '<p><a href="/url" title="t">a</a></p>\n',
+    );
+  });
+});