fix @babel/traverse path cache workaround not needed in latest babel (#1650)

vzaidman · meta-codesync[bot] · commit 3952cb70ecb6 · 2026-02-09T13:21:40.000-08:00
Summary: Pull Request resolved: #1650 [#17708](babel/babel#17708) fixes the longstanding `babel/traverse` pollution issue in [v7.29.0](https://github.com/babel/babel/releases/tag/v7.29.0). This diff opts-out of the workaround if the version of traverse is above the version where it was fixed. Changelog: Internal Reviewed By: robhogan Differential Revision: D92710292 fbshipit-source-id: 6b202c001cdf5d2ec02c81c3e9f280752d83c998
diff --git a/packages/metro-source-map/package.json b/packages/metro-source-map/package.json
@@ -32,7 +32,8 @@
   "devDependencies": {
     "@babel/core": "^7.25.2",
     "@babel/parser": "^7.25.3",
-    "terser": "^5.15.0"
+    "terser": "^5.15.0",
+    "semver": "^7.1.3"
   },
   "engines": {
     "node": ">=20.19.4"
diff --git a/packages/metro-source-map/src/__tests__/generateFunctionMap-test.js b/packages/metro-source-map/src/__tests__/generateFunctionMap-test.js
@@ -33,6 +33,15 @@ const {
   SourceMetadataMapConsumer,
 } = require('metro-symbolicate/private/Symbolication');
 
+// $FlowFixMe[cannot-resolve-module] - reading version from package.json
+// $FlowFixMe[untyped-import]
+const babelTraverseVersion = require('@babel/traverse/package.json').version;
+// $FlowFixMe[untyped-import]
+const babelTraverseCacheBugFixed = require('semver').gte(
+  babelTraverseVersion,
+  '7.29.0',
+);
+
 function getAst(source: string) {
   return parse(source, {
     plugins: ['classProperties', 'dynamicImport', 'jsx', 'flow'],
@@ -1902,8 +1911,19 @@ window.foo();
       // Perform a trivial traversal.
       traverse(ast, {});
 
-      // Expect that the path cache is polluted with entries lacking `hub`.
-      expect(() => expectTransformPathesToHaveHub(ast)).toThrow();
+      try {
+        if (babelTraverseCacheBugFixed) {
+          expect(() => expectTransformPathesToHaveHub(ast)).not.toThrow();
+        } else {
+          // Expect that the path cache is polluted with entries lacking `hub`.
+          expect(() => expectTransformPathesToHaveHub(ast)).toThrow();
+        }
+      } catch (e) {
+        console.error(
+          'Test failed with @babel/traverse version: ' + babelTraverseVersion,
+        );
+        throw e;
+      }
     });
 
     test('successfully works around traverse cache pollution', () => {
@@ -1914,6 +1934,10 @@ window.foo();
     });
 
     test('does not reset the path cache', () => {
+      if (babelTraverseCacheBugFixed) {
+        return;
+      }
+
       const dummyCache: Map<unknown, unknown> = new Map();
       // $FlowFixMe[prop-missing] - Writing to readonly map for test purposes.
       traverse.cache.path.set(ast, dummyCache);
diff --git a/packages/metro-source-map/src/generateFunctionMap.js b/packages/metro-source-map/src/generateFunctionMap.js
@@ -11,13 +11,11 @@
 
 import type {FBSourceFunctionMap} from './source-map';
 import type {PluginObj} from '@babel/core';
-import type {NodePath} from '@babel/traverse';
+import type {NodePath, Traverse} from '@babel/traverse';
 import type {Node as BabelNode} from '@babel/types';
 import type {MetroBabelFileMetadata} from 'metro-babel-transformer';
 
 import B64Builder from './B64Builder';
-// $FlowFixMe[cannot-resolve-module] - resolves to @babel/traverse
-import traverseForGenerateFunctionMap from '@babel/traverse--for-generate-function-map';
 import * as t from '@babel/types';
 import {
   isAssignmentExpression,
@@ -46,6 +44,29 @@ import invariant from 'invariant';
 import nullthrows from 'nullthrows';
 import fsPath from 'path';
 
+// $FlowFixMe[untyped-import]
+import semver from 'semver';
+
+const isBabelTraverseCacheBugFixed = semver.gte(
+  // $FlowFixMe[cannot-resolve-module] - reading version from package.json
+  // $FlowFixMe[untyped-import]
+  require('@babel/traverse/package.json').version, // eslint-disable-line import/no-commonjs
+  '7.29.0',
+);
+
+// TODO: when babel is bumpedabove 7.29.0, remove:
+//  - this workaround
+//  - the '@babel/traverse--for-generate-function-map' dependency from "package.json"
+//  - the test from this workaround from "generateFunctionMap-test.js"
+// Before Babel 7.29.0, "traverse" populates/pollutes the path cache (`traverse.cache.path`)
+// with values missing the `hub` property needed by Babel transformation, so we
+// use a separate copy of traverse to populate a separate cache to not pollute
+// the main @babel/traverse cache. See: https://github.com/facebook/metro/pull/1340
+const traverseFixed: Traverse = isBabelTraverseCacheBugFixed
+  ? require('@babel/traverse').default
+  : // $FlowFixMe[cannot-resolve-module] - resolves to @babel/traverse
+    require('@babel/traverse--for-generate-function-map').default;
+
 type Position = {
   line: number,
   column: number,
@@ -218,11 +239,7 @@ function forEachMapping(
 ) {
   const visitor = getFunctionMapVisitor(context, pushMapping);
 
-  // Traversing populates/pollutes the path cache (`traverse.cache.path`) with
-  // values missing the `hub` property needed by Babel transformation, so we
-  // use a separate copy of traverse to populate a separate cache to not pollute
-  // the main @babel/traverse cache. See: https://github.com/facebook/metro/pull/1340
-  traverseForGenerateFunctionMap(ast, {
+  traverseFixed(ast, {
     // Our visitor doesn't care about scope
     noScope: true,
 
diff --git a/yarn.lock b/yarn.lock
@@ -4952,6 +4952,11 @@ semver@^6.0.0, semver@^6.3.0, semver@^6.3.1:
   resolved "https://registry.yarnpkg.com/semver/-/semver-6.3.1.tgz#556d2ef8689146e46dcea4bfdd095f3434dffcb4"
   integrity sha512-BR7VvDCVHO+q2xBEWskxS6DJE1qRnb7DxzUrogb71CWoSficBxYsiAGd+Kl0mmq/MprG9yArRkyrQxTO6XjMzA==
 
+semver@^7.1.3:
+  version "7.7.4"
+  resolved "https://registry.yarnpkg.com/semver/-/semver-7.7.4.tgz#28464e36060e991fa7a11d0279d2d3f3b57a7e8a"
+  integrity sha512-vFKC2IEtQnVhpT78h1Yp8wzwrf8CM+MzKMHGJZfBtzhZNycRFnXsHk6E5TxIkkMsgNS7mdX3AGB7x2QM2di4lA==
+
 semver@^7.3.5, semver@^7.5.3, semver@^7.5.4, semver@^7.6.0:
   version "7.6.3"
   resolved "https://registry.yarnpkg.com/semver/-/semver-7.6.3.tgz#980f7b5550bc175fb4dc09403085627f9eb33143"
