Fix quadratic compexity on backticks

close https://github.com/markdown-it/markdown-it/issues/736

CHANGELOG.md

@@ -12,7 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `[](url (xxx())` is no longer a valid link.
 - `[](url\ xxx)` is no longer a valid link.
 - Fix performance issues when parsing links, #732, #734.
-- Fix performance issues when parsing backticks, #733.
+- Fix performance issues when parsing backticks, #733, #736.
 - Fix performance issues when parsing emphases, #735.
 
 

lib/rules_inline/backticks.js

@@ -52,13 +52,11 @@ module.exports = function backtick(state, silent) {
 
     // Some different length found, put it in cache as upper limit of where closer can be found
     state.backticks[closerLength] = matchStart;
-
-    // Scanned through the end, didn't find anything
-    if (matchEnd >= max) {
-      state.backticksScanned = true;
-    }
   }
 
+  // Scanned through the end, didn't find anything
+  state.backticksScanned = true;
+
   if (!silent) state.pending += marker;
   state.pos += openerLength;
   return true;

test/pathological.js

@@ -122,5 +122,9 @@ describe('Pathological sequences speed', () => {
     it('emphasis **_* pattern', async () => {
       await test_pattern('**_* '.repeat(50000));
     });
+
+    it('backtick ``\\``\\`` pattern', async () => {
+      await test_pattern('``\\'.repeat(50000));
+    });
   });
 });