feat: plugin support by bjohansebas · Pull Request #5650 · webpack/webpack-dev-server

bjohansebas · 2026-02-21T18:16:50Z

Summary

What kind of change does this PR introduce?

Did you add tests for your changes?

Does this PR introduce a breaking change?

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

codecov · 2026-02-21T18:19:51Z

Codecov Report

❌ Patch coverage is 97.01493% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.97%. Comparing base (4810909) to head (6efe969).

Files with missing lines	Patch %	Lines
lib/Server.js	97.01%	4 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (4810909) and HEAD (6efe969). Click for more details.

HEAD has 63 uploads less than BASE

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Additional details and impacted files

@@            Coverage Diff             @@
##             next    #5650      +/-   ##
==========================================
- Coverage   88.93%   81.97%   -6.96%     
==========================================
  Files          13       13              
  Lines        5919     6037     +118     
==========================================
- Hits         5264     4949     -315     
- Misses        655     1088     +433

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alexander-akait · 2026-02-21T19:06:48Z

We should start it in webpack-dev-middleware, currently webpack-dev-middleware uses console.log to output stats, it means we will spam logs, we need an options or another function wrapper - require("webpack-dev-middleware").plugin(options)

bjohansebas

These changes should work without requiring any changes to webpack-cli yet. Once this is merged, we can work on a patch for webpack-cli to use the plugin support, but it is independent of changes to webpack-cli.

bjohansebas · 2026-05-07T05:55:44Z

cc: @alexander-akait friendly ping for feedback

alexander-akait · 2026-05-08T15:17:30Z

Will look soon, I little bit busy, we should make the new major release the next week, I will help you to finish remains tasks

alexander-akait · 2026-05-11T16:31:45Z

@bjohansebas let's rebase

alexander-akait · 2026-05-18T15:28:21Z

@bjohansebas can take a look at our failed tests, a lot of PRs without green, we need to resolve it, thanks

bjohansebas · 2026-05-22T05:24:13Z

@bjohansebas can take a look at our failed tests, a lot of PRs without green, we need to resolve it, thanks

Those are just flaky tests, like before. You just need to rerun them and that's it.

alexander-akait · 2026-05-22T08:57:15Z

Looks like problem with lint here

alexander-akait · 2026-06-04T15:20:06Z

+    // the user is not in control of the plugin lifecycle here, so we stay
+    // silent rather than logging a warning.
+    const isBuildMode = () =>
+      childCompilers.every((child) => !child.watching && !child.options.watch);


Each compiler have watching when it is watching, no need to check on watch, at least I can see situation when watch will be true, but watching undefined

alexander-akait · 2026-06-04T15:20:34Z

+      if (seenFirstDone.has(childCompiler)) return;
+      seenFirstDone.add(childCompiler);
+      firstDoneCount++;
+      if (firstDoneCount < childCompilers.length) return;


Can you clarify when we need firstDoneCount?

alexander-akait · 2026-06-04T15:22:03Z

+      childCompiler.hooks.done.tapPromise(pluginName, () =>
+        onChildDone(childCompiler),
+      );
+      childCompiler.hooks.shutdown.tapPromise(pluginName, onChildShutdown);


Ideally we should have the same hooks for multi compiler, and so don't use for/of, but we can postpone it and improve later

alexander-akait · 2026-06-04T15:22:33Z

+    };
+
+    for (const childCompiler of childCompilers) {
+      childCompiler.hooks.beforeCompile.tapPromise(pluginName, ensureSetup);


Can we avoid beforeCompile at all, it is unsafe in some cases, ideally we should use only done and shutdown

I think we can done everything on done, also please add a test case what we really change outputFileSystem and use it, not webpack built-in the real fs

Doing it only through done is complicated because there are processes that need to be initialized much earlier. That's why beforeCompile is used.

bjohansebas · 2026-06-09T14:01:00Z

okay tomorrow i will continue with this

changeset-bot · 2026-06-15T14:42:43Z

🦋 Changeset detected

Latest commit: 6efe969

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

This PR includes changesets to release 1 package

Name	Type
webpack-dev-server	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

Allow webpack-dev-server to run as a webpack plugin. The server can now be created without explicitly passing a compiler, integrates with the compiler lifecycle to prevent multiple starts on recompilation, ensures clean shutdown, and supports MultiCompiler setups with multiple independent plugin servers.

Add e2e coverage for the plugin API (api-plugin.test.js), MultiCompiler and multiple independent plugin servers, build-mode behavior, and related logging snapshots. Add the compile helper and port mappings used by these tests.

Add a runnable example (app, webpack config and README) showing how to configure and use webpack-dev-server as a webpack plugin.

…etter handling of compiler events

bjohansebas · 2026-06-15T17:55:27Z

`watchRun` vs `beforeCompile`

setup() must run before the first compilation writes assets, because webpack-dev-middleware replaces outputFileSystem with an in-memory filesystem. Running only on done is too late—the first build has already written to disk.

Both watchRun and beforeCompile run before emit, but watchRun is a better fit because it is watch-only (no build-mode guard required) and, on a MultiCompiler, a single top-level tap covers all child compilers.

Why not do everything on `done`?

done fires after emit, so it's too late for setup that needs to affect the compilation output. The only thing that belongs on done is listen(), since the HTTP server should start after the first successful build.

Why use `shutdown`?

Teardown needs to work when compiler.close() is called. On a MultiCompiler, the aggregate watchClose does not fire for compiler.close(), while child shutdown hooks do.

shutdown is also async, allowing compiler.close() to wait for the server to fully stop and release its port before returning.

bjohansebas force-pushed the plugin-support branch from 0d79407 to 8664549 Compare March 30, 2026 19:43

alexander-akait reviewed Mar 31, 2026

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Comment thread lib/Server.js Outdated

alexander-akait reviewed Mar 31, 2026

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Comment thread lib/Server.js Outdated

bjohansebas force-pushed the plugin-support branch from d8084a7 to 9890a76 Compare April 1, 2026 23:07

alexander-akait reviewed Apr 2, 2026

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Comment thread test/e2e/api.test.js Outdated

bjohansebas force-pushed the plugin-support branch from 9890a76 to 616b803 Compare April 26, 2026 18:50

bjohansebas marked this pull request as ready for review May 1, 2026 20:49

bjohansebas requested a review from alexander-akait May 1, 2026 21:07

bjohansebas commented May 1, 2026

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bjohansebas force-pushed the plugin-support branch 2 times, most recently from 1060a9c to 4591762 Compare May 16, 2026 17:54

bjohansebas force-pushed the plugin-support branch from bb3626c to 9912722 Compare May 22, 2026 05:07

bjohansebas force-pushed the next branch from cd007a3 to 6550a05 Compare May 23, 2026 16:22

bjohansebas force-pushed the plugin-support branch 2 times, most recently from 0102816 to 2d6d746 Compare May 23, 2026 18:52

alexander-akait reviewed Jun 4, 2026

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bjohansebas force-pushed the next branch 2 times, most recently from c2dd24b to 4810909 Compare June 12, 2026 22:46

bjohansebas force-pushed the plugin-support branch from b2914df to 5be7251 Compare June 15, 2026 14:42

bjohansebas added 3 commits June 15, 2026 09:47

test: add tests for plugin support

33fedcc

Add e2e coverage for the plugin API (api-plugin.test.js), MultiCompiler and multiple independent plugin servers, build-mode behavior, and related logging snapshots. Add the compile helper and port mappings used by these tests.

docs: add example for using webpack-dev-server as a plugin

07b85dc

Add a runnable example (app, webpack config and README) showing how to configure and use webpack-dev-server as a webpack plugin.

bjohansebas force-pushed the plugin-support branch from 5be7251 to 07b85dc Compare June 15, 2026 14:51

bjohansebas added 4 commits June 15, 2026 09:53

chore: add changeset for plugin support

0a6871c

test: add test for in-memory file system behavior in plugin

6c929cb

refactor: update hooks to use watchRun instead of beforeCompile for b…

75801a9

…etter handling of compiler events

test: add hot module replacement tests for plugin API

6b935d7

bjohansebas added 2 commits June 15, 2026 13:08

test: enhance output.clean behavior test for in-memory asset serving

e9da189

test: log listen() failure instead of throwing in server setup

6efe969

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bjohansebas commented Jun 15, 2026

watchRun vs beforeCompile

Why not do everything on done?

Why use shutdown?

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codecov Bot commented Feb 21, 2026 •

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changeset-bot Bot commented Jun 15, 2026 •

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`watchRun` vs `beforeCompile`

Why not do everything on `done`?

Why use `shutdown`?