feat: add webpack 4 support to ts-loader v9 by Copilot · Pull Request #1697 · TypeStrong/ts-loader

Copilot · 2026-05-21T17:11:42Z

Identify actionable new @copilot comments
Review the full PR diff for correctness, compatibility, and risk
Summarize key strengths, concerns, and follow-up recommendations
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Agent-Logs-Url: https://github.com/TypeStrong/ts-loader/sessions/74b74f2d-76ad-4022-9635-77d0c5acce76 Co-authored-by: johnnyreilly <[email protected]>

Agent-Logs-Url: https://github.com/TypeStrong/ts-loader/sessions/e322b7ed-e010-4d60-9a2d-3672c9d55324 Co-authored-by: johnnyreilly <[email protected]>

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johnnyreilly · 2026-05-21T19:20:12Z

@copilot please consistently use instance.isWebpack5 to decide strategy

Agent-Logs-Url: https://github.com/TypeStrong/ts-loader/sessions/84c8d79e-30f1-46f5-baf3-bc669466d3ba Co-authored-by: johnnyreilly <[email protected]>

Copilot · 2026-05-21T19:23:59Z

@copilot please consistently use instance.isWebpack5 to decide strategy

Done in 5d7ab2f. I updated the remaining strategy checks to consistently branch on instance.isWebpack5 (including cached/reused instance paths and build-dependency registration) rather than using direct feature detection at those decision points.

johnnyreilly · 2026-05-21T19:44:31Z

 } from './interfaces';
 import { getInputFileNameFromOutput } from './instances';
+
+export const isWebpack5 = !!(webpack as any).sources;


Is this necessary @copilot?

Good catch — no, it wasn’t necessary there. I removed isWebpack5 from utils.ts and localized detection to instance setup in instances.ts in 78fa91f, so strategy still flows through instance.isWebpack5 without the extra utils export.

Agent-Logs-Url: https://github.com/TypeStrong/ts-loader/sessions/faa27c75-efcd-4e5a-8062-443dce3bf610 Co-authored-by: johnnyreilly <[email protected]>

johnnyreilly · 2026-05-21T20:05:52Z

-      (error: any) => error.loaderSource !== tsLoaderSource(loaderOptions)
-    )
-    .forEach(error => module.addError(error));
+  const webpackModule = module as any;


@copilot I don't think the webpack5 code needs to use webpackModule it can use module

Updated in 7b3cd3e — webpack 5 path now uses module directly (getWarnings/getErrors/clearWarningsAndErrors) and keeps webpackModule only for the webpack 4 branch.

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Copilot · 2026-05-21T20:12:17Z

@copilot please consistently use instance.isWebpack5 to decide strategy

Handled in 5d7ab2f and retained in follow-ups: strategy decisions branch on instance.isWebpack5 consistently.

johnnyreilly · 2026-05-25T09:24:18Z

Starting to write this up here: johnnyreilly/blog.johnnyreilly.com#1109

johnnyreilly · 2026-05-25T09:33:44Z

@copilot review the src/**.*ts files in this PR with an eye to identifying any potential performance issues this PR could introduce. There may be none. Tell me what issues might exist. Make no changes - let me decide.

Copilot · 2026-05-25T09:37:56Z

@copilot review the src/**.*ts files in this PR with an eye to identifying any potential performance issues this PR could introduce. There may be none. Tell me what issues might exist. Make no ch...

Reviewed at 06def35 with a performance-focused pass over src/**/*.ts changes in this PR. I don’t see any high-confidence new perf regressions.

Possible low-risk hotspots to keep an eye on:

src/after-compile.ts:131-146 (determineModules): now also checks resourceResolveData?.path; this may increase modules considered in the map in some builds.
src/watch-run.ts:42-49 (timestamp normalization): extra per-file branching on each watch cycle; likely negligible, but it is new work on very large file sets.

Everything else I reviewed looks neutral or slightly better for runtime cost (no obvious new heavy loops/allocations in hot paths). No code changes made.

johnnyreilly · 2026-05-26T07:17:04Z

@copilot please review this PR and give me your thoughts

Copilot · 2026-05-26T07:19:42Z

@copilot please review this PR and give me your thoughts

My review on 8332763:

Overall this is in good shape and I think the webpack 4 support direction is sound. The latest branch CI I checked for this head is green (build and test completed successfully).

What looks strong:

Optional loader-utils peer dependency with webpack-4-only runtime loading is a good compatibility strategy.
The webpack 4 module error normalization path in after-compile now behaves consistently with restored comparison snapshots.
The watch timestamp handling changes look robust across webpack timestamp shapes.

Things I’d keep an eye on before merge:

Version strategy is now partly driven by global webpack.version (src/loaderUtils.ts) rather than only a passed-through per-instance flag; that’s workable but a potential future drift point.
determineModules now also uses resourceResolveData?.path (src/after-compile.ts), which can increase module map population in large compilations (likely low risk, but worth noting).
yarn.lock churn is large; if possible, keep it as tight as practical.

I don’t see a clear blocker in the current state.

johnnyreilly · 2026-05-27T04:55:59Z

@copilot a tester reported this issue:

Syntax Error: TypeError: module.addError is not a function at Array.forEach ()

Can you identify where that might have come from?

feat: widen webpack peer support

8465fa4

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Copilot AI assigned Copilot and johnnyreilly May 21, 2026

Copilot created this pull request from a session on behalf of johnnyreilly May 21, 2026 17:11 View session

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chore: plan isWebpack5 refactor

a896f16

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refactor: propagate webpack major version through instance flow

cf368a5

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johnnyreilly changed the title ~~Align webpack support metadata with current CI coverage~~ Experiment with adding webpack 4 support back May 21, 2026

refactor: use instance.isWebpack5 consistently for strategy decisions

5d7ab2f

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Copilot finished work on behalf of johnnyreilly May 21, 2026 19:24

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refactor: localize webpack5 detection to instance setup

78fa91f

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refactor: use module methods directly in webpack5 error cleanup

7b3cd3e

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chore: drop old

06def35

Copilot started work on behalf of johnnyreilly May 25, 2026 09:33 View session

Copilot finished work on behalf of johnnyreilly May 25, 2026 09:38

johnnyreilly added 9 commits May 25, 2026 10:39

fix: make loader-utils * as a peerDependencies

d74e919

fix: watchRun should cater for webpack 4 dates

351a12e

fix: webpack 4 errors

811d8e5

fix: lint

8e001a6

fix: loaderSource -> details

05d766d

fix: WebpackError wouldn't work for webpack 4

e1fe960

fix: nits

30b3597

fix: whoops

c4fb493

fix: do not use SourceMapConsumer if correct version not available

8332763

Copilot started work on behalf of johnnyreilly May 26, 2026 07:17 View session

Copilot finished work on behalf of johnnyreilly May 26, 2026 07:20

chore: experiment removing resourceResolveData

b14e37c

johnnyreilly mentioned this pull request May 26, 2026

ts-loader supports webpack 4 again johnnyreilly/blog.johnnyreilly.com#1109

Merged

Copilot started work on behalf of johnnyreilly May 27, 2026 04:56 View session

fix: guard module.addError for webpack 4

e6a336f

Copilot finished work on behalf of johnnyreilly May 27, 2026 05:13

johnnyreilly added 2 commits May 27, 2026 07:35

feat: add common addErrorToModule

987f11f

chore: CHANGELOG

157835c

johnnyreilly approved these changes May 27, 2026

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johnnyreilly changed the title ~~Experiment with adding webpack 4 support back~~ feat: add webpack 4 support to ts-loader v9 May 27, 2026

johnnyreilly merged commit d088b15 into main May 27, 2026
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