perf: share the compile cache with child processes and worker threads by alexander-akait · Pull Request #4872 · webpack/webpack-cli

alexander-akait · 2026-10-16T02:03:23Z

Summary

enableCompileCache() only covers the CLI's own thread, so minimizer workers (terser, css/html minimizers) and any other child process or worker thread compiled every module from scratch. The CLI now sets NODE_COMPILE_CACHE to the cache directory, which Node reads at startup, unless the environment already names one or disables the cache. This is the same fix as webpack/webpack#22706 made in webpack/bin/webpack.js; running webpack-cli directly still missed it.

// before
enableCompileCache();

// after
const { directory } = enableCompileCache();
if (directory && process.env.NODE_COMPILE_CACHE === undefined) {
  process.env.NODE_COMPILE_CACHE = directory;
}

What a config run by the CLI sees (Node 22.22):

	Before	After
CLI process	`/tmp/node-compile-cache/v22.22.0-…`	`/tmp/node-compile-cache/v22.22.0-…`
child process	`undefined`	`/tmp/node-compile-cache/v22.22.0-…`
worker thread	`undefined`	`/tmp/node-compile-cache/v22.22.0-…`

Production build with 8 entries (terser runs in its workers), warm cache, median of 5 runs: 802 ms → 750 ms.

What kind of change does this PR introduce?

perf

Did you add tests for your changes?

Yes: test/build/compile-cache/compile-cache.test.js. The config starts a child process and a worker thread and reports the cache directory each one sees. It covers handing the cache on, keeping a directory set in the environment, and NODE_DISABLE_COMPILE_CACHE. The first case fails without the fix. On Node 20 (no compile cache), it checks that nothing is handed on. I ran it on Node 22 and Node 20.

Does this PR introduce a breaking change?

No.

If relevant, what needs to be documented once your changes are merged or what have you already documented?

n/a

Use of AI

Written with Claude Code: it compared the CLI with the webpack fix, reproduced the missing cache in child processes and worker threads, wrote the fix and the test, and measured the build. Directed and reviewed by the author.

🤖 Generated with Claude Code

https://claude.ai/code/session_01QYPkbvwyRWt2SHgXDoYRdo

Generated by Claude Code

Summary by CodeRabbit

New Features
- Compile-cache settings are shared with child processes and worker threads, allowing them to reuse the same cache directory.
- An explicitly configured NODE_COMPILE_CACHE value is preserved, and preload-enabled caching avoids adding another directory setting.
- Compile caching remains disabled when NODE_DISABLE_COMPILE_CACHE is set.
- When compile-cache support is unavailable, child processes and workers continue without a cache directory.

`enableCompileCache()` only covers the current thread, so minimizer workers and other child processes compiled every module from scratch. Setting `NODE_COMPILE_CACHE` to the cache directory hands it to them at startup, unless the environment already names one or disables the cache.

changeset-bot · 2026-10-16T02:03:28Z

🦋 Changeset detected

Latest commit: 0b7bf17

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
webpack-cli	Patch

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github-actions · 2026-10-16T02:04:03Z

This PR is packaged and the instant preview is available (3af13e1).

Install it locally:

npm

npm i -D webpack-cli@https://pkg.pr.new/webpack-cli@3af13e1

yarn

yarn add -D webpack-cli@https://pkg.pr.new/webpack-cli@3af13e1

pnpm

pnpm add -D webpack-cli@https://pkg.pr.new/webpack-cli@3af13e1

codecov · 2026-10-16T02:05:23Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.84%. Comparing base (5d4e9e4) to head (0b7bf17).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4872      +/-   ##
==========================================
- Coverage   94.86%   94.84%   -0.02%     
==========================================
  Files          14       14              
  Lines        5626     5626              
  Branches      841      841              
==========================================
- Hits         5337     5336       -1     
- Misses        288      289       +1     
  Partials        1        1

see 1 file with indirect coverage changes

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coderabbitai · 2026-10-16T02:06:33Z

No actionable comments were generated in the recent review. 🎉

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📒 Files selected for processing: 4

packages/webpack-cli/bin/cli.js
test/build/compile-cache/compile-cache.test.js
test/build/compile-cache/preload.js
test/build/compile-cache/webpack.config.js

🚧 Files skipped from review as they are similar to previous changes: 1

test/build/compile-cache/webpack.config.js

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Walkthrough

The CLI now stores the directory returned by enableCompileCache() and sets NODE_COMPILE_CACHE when compile caching is enabled and the variable is unset. New tests check compile-cache paths reported by the CLI, a child process, and a worker. They also check behavior when a cache directory is configured, compile-cache support is unavailable, or NODE_DISABLE_COMPILE_CACHE is set to "1".

Priority: ➖ Normal

Merge Risk: ⚪ Minimal · up to 0b7bf

The CLI and its child processes and workers use the same compile cache, including when a preload enabled it first. No actionable merge risk remains in the reviewed change.

Pre-merge checks: 5

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: sharing the compile cache with child processes and worker threads.
Docstring Coverage		No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 5…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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packages/webpack-cli/bin/cli.js

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test/build/compile-cache/compile-cache.test.js

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ESLint: 10.12.0

Error: Error while loading rule 'jest/no-deprecated-functions': Unable to detect Jest version - please ensure jest package is installed, or otherwise set version explicitly
Occurred while linting /test/build/compile-cache/compile-cache.test.js
at detectJestVersion (/.eslint-tmp/node_modules/eslint-plugin-jest/lib/rules/utils/detectJestVersion.js:22:9)
at create (/.eslint-tmp/node_modules/eslint-plugin-jest/lib/rules/no-deprecated-functions.js:31:107)
at Object.create (/.eslint-tmp/node_modules/@typescript-eslint/utils/dist/eslint-utils/RuleCreator.js:39:20)
at createRuleListeners (/.eslint-tmp/node_modules/eslint/lib/linter/linter.js:502:15)
at /.eslint-tmp/node_modules/eslint/lib/linter/linter.js:628:7
at Array.forEach ()
at runRules (/.eslint-tmp/node_modules/eslint/lib/linter/linter.js:562:31)
at #flatVerifyWithoutProcessors (/.eslint-tmp/node_modules/eslint/lib/linter/linter.js:1297:4)
at Linter._verifyWithFlatConfigArrayAndWithoutProcessors (/.eslint-tmp/node_modules/eslint/lib/linter/linter.js:1382:43)
at Linter._verifyWithFlatConfigArray (/.eslint-tmp/node_modules/eslint/lib/linter/linter.js:1449:15)

test/build/compile-cache/preload.js

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test/build/compile-cache/webpack.config.js

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Actionable comments posted: 2

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packages/webpack-cli/bin/cli.js
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test/build/compile-cache/webpack.config.js

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A cache a preload already enabled reports its version-tagged directory, which a child would tag again. Also exit the test config from the write callback so the report survives an asynchronous pipe.

coderabbitai Bot reviewed Oct 16, 2026

View reviewed changes

Comment thread packages/webpack-cli/bin/cli.js Outdated

Comment thread test/build/compile-cache/webpack.config.js Outdated

fix: forward the compile cache only when the CLI enabled it

0b7bf17

A cache a preload already enabled reports its version-tagged directory, which a child would tag again. Also exit the test config from the write callback so the report survives an asynchronous pipe.

alexander-akait mentioned this pull request Oct 16, 2026

fix: forward the compile cache only when the CLI enabled it webpack/webpack#22722

Merged

alexander-akait merged commit 3af13e1 into main Oct 16, 2026
40 of 41 checks passed

alexander-akait deleted the bugfix/share-compile-cache-with-child-processes branch October 16, 2026 08:56

github-actions Bot mentioned this pull request Oct 16, 2026

chore(release): new release #4841

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perf: share the compile cache with child processes and worker threads - #4872

perf: share the compile cache with child processes and worker threads#4872
alexander-akait merged 2 commits into
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