fix(plugin): resolve crash on invalidate() in plugin mode

[bjohansebas]

When used as a plugin the host (webpack-cli, webpack-dev-server, etc.) owns compiler.watch(), so invalidate() threw because the middleware has no watching of its own. Invalidate the host's watching instead (each child compiler's one for a MultiCompiler on webpack < 5.109) and warn when the compiler is not watching at all.

Summary

What kind of change does this PR introduce?

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Use of AI

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Note

Low Risk
Targeted fix to public invalidate() behavior in plugin mode with tests; standalone path unchanged when middleware owns watching.

Overview
Fixes a crash when invalidate() is called while webpack-dev-middleware runs as a plugin (isPlugin = true), where the middleware no longer owns a watching instance.

invalidate() now uses the middleware’s own watching when present (standalone usage). In plugin mode it forwards invalidation to the host’s compiler.watching, or to each child compiler’s watching on MultiCompiler when top-level watching is missing (webpack < 5.109). If nothing is watching, it logs a warning instead of throwing—aligned with existing plugin-mode close() behavior.

Plugin-mode tests cover host-owned invalidation and the no-watch warning; a changeset records the patch.

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[changeset-bot]

🦋 Changeset detected

Latest commit: c801900

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-middleware	Patch

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[codecov]

Codecov Report

❌ Patch coverage is 73.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.44%. Comparing base (ac84095) to head (c801900).

Files with missing lines	Patch %	Lines
src/index.js	73.33%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2378      +/-   ##
==========================================
- Coverage   92.73%   92.44%   -0.30%     
==========================================
  Files           3        3              
  Lines        1005     1019      +14     
  Branches      312      317       +5     
==========================================
+ Hits          932      942      +10     
- Misses         65       68       +3     
- Partials        8        9       +1     

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[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

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[cursor]

Missing callback on invalidate no-op

Medium Severity

The !invalidated guard warns but never invokes the callback, unlike close(). Because middleware.ready already ran, a provided callback can stay queued forever when state is false, so callers waiting on invalidate(callback) hang. This violates the plugin-mode guard pattern that requires warning and completing the callback on no-op paths.

Additional Locations (1)

• src/index.js#L596-L598

 

^{Triggered by learned rule: Plugin mode guards must log warnings, not silently no-op}

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