fix: fsync: false when writing cache files

We're using writeFileAtomic here in order to get atomic rename, not
to get full system power failure resilience. Most(tm) filesystems
will guarantee either/or during a crash here, which is plenty
enough for us.

fsync is a nearly 3x slowdown for me, ts-jest'ing my whole codebase
(~900 files in testcase).

CHANGELOG.md

@@ -7,6 +7,7 @@
 - `[jest-haste-map]` [**BREAKING**] Remove `mapper` option ([#9581](https://github.com/facebook/jest/pull/9581))
 - `[*]` Support array of paths for `moduleNameMapper` aliases ([#9465](https://github.com/facebook/jest/pull/9465))
 - `[jest-reporters]` Adds ability to pass options to the istanbul-reporter through `coverageReporters` ([#9572](https://github.com/facebook/jest/pull/9572))
+- `[jest-transform]` `writeCacheFile` no longer calls `fsync` ([#9605](https://github.com/facebook/jest/pull/9572))
 
 ### Fixes
 

packages/jest-transform/src/ScriptTransformer.ts

@@ -630,7 +630,7 @@ function readCodeCacheFile(cachePath: Config.Path): string | null {
  */
 const writeCacheFile = (cachePath: Config.Path, fileData: string) => {
   try {
-    writeFileAtomic(cachePath, fileData, {encoding: 'utf8'});
+    writeFileAtomic(cachePath, fileData, {encoding: 'utf8', fsync: false});
   } catch (e) {
     if (cacheWriteErrorSafeToIgnore(e, cachePath)) {
       return;