Add caching of traversed paths to no-cycle

- This leads to about a 5x speed up

Signed-off-by: Sebastian Malton <sebastian@malton.name>

src/rules/no-cycle.js

@@ -9,6 +9,8 @@ import { isExternalModule } from '../core/importType';
 import moduleVisitor, { makeOptionsSchema } from 'eslint-module-utils/moduleVisitor';
 import docsUrl from '../docsUrl';
 
+const traversed = new Set();
+
 // todo: cache cycles / deep relationships for faster repeat evaluation
 module.exports = {
   meta: {
@@ -35,8 +37,9 @@ module.exports = {
       },
     })],
   },
-
-  create(context) {
+  _traversed: traversed,
+  create: (context) => {
+    // const traversed = new Set();
     const myPath = context.getPhysicalFilename ? context.getPhysicalFilename() : context.getFilename();
     if (myPath === '<text>') return {}; // can't cycle-check a non-file
 
@@ -75,7 +78,6 @@ module.exports = {
       }
 
       const untraversed = [{ mget: () => imported, route:[] }];
-      const traversed = new Set();
       function detectCycle({ mget, route }) {
         const m = mget();
         if (m == null) return;

tests/src/rules/no-cycle.js

@@ -2,6 +2,7 @@ import { parsers, test as _test, testFilePath } from '../utils';
 
 import { RuleTester } from 'eslint';
 import flatMap from 'array.prototype.flatmap';
+import { beforeEach } from 'mocha';
 
 const ruleTester = new RuleTester();
 const rule = require('rules/no-cycle');
@@ -14,6 +15,10 @@ const test = def => _test(Object.assign(def, {
 
 const testDialects = ['es6'];
 
+beforeEach(() => {
+  rule._traversed.clear();
+});
+
 ruleTester.run('no-cycle', rule, {
   valid: [].concat(
     // this rule doesn't care if the cycle length is 0