Enable noUncheckedSideEffectImports by default
#62443
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RyanCavanaugh
added
Breaking Change
typescript-bot
added
Author: Team
For Milestone Bug
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Pull Request Overview
This PR enables the noUncheckedSideEffectImports compiler option by default. The option checks that side effect imports (imports without bindings like import "module") can be properly resolved, helping to catch errors where modules cannot be found or resolved.
Key changes:
- Changed the default value from
falsetotruefor thenoUncheckedSideEffectImportsoption - Updated compiler logic to enable the flag by default
- Added test suppressions for existing tests that relied on the old behavior
Reviewed Changes
Copilot reviewed 34 out of 34 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
src/compiler/commandLineParser.ts |
Changed default value description from false to true |
src/compiler/checker.ts |
Updated logic to enable flag by default using !== false instead of !! |
| Multiple test files | Added // @noUncheckedSideEffectImports: false directive to preserve existing test behavior |
| Test baseline files | Updated error outputs to reflect new default behavior catching side effect import errors |
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@typescript-bot test it |
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Hey @RyanCavanaugh, the results of running the DT tests are ready. There were interesting changes: Branch only errors:Package: chai-like Package: splitting Package: chai-json-schema Package: react-katex Package: vue-moment Package: dirty-chai Package: redux-shortcuts Package: react-smartbanner Package: bmapgl-browser Package: chai-subset Package: vue3-carousel-3d Package: babel-types Package: chai-string Package: chai-fs Package: karma-chai Package: node/v18 Package: chai-spies Package: page-flip Package: rangy Package: tablesorter Package: hapi Package: hapi/v17 Package: chai-arrays Package: wonder.js Package: gun |
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@RyanCavanaugh Here are the results of running the user tests with tsc comparing There were infrastructure failures potentially unrelated to your change:
Otherwise... Everything looks good! |
jakebailey
reviewed
Sep 12, 2025
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| import "./extention"; | ||
| ~~~~~~~~~~~~~ | ||
| !!! error TS2307: Cannot find module './extention' or its corresponding type declarations. |
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Weird, why doesn't this work?
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Because we wrote extention (t) and the file is called extension (s), lmao
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@RyanCavanaugh Here they are:
tscComparison Report - baseline..pr
System info unknown
Hosts
Scenarios
Developer Information: |
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@RyanCavanaugh Here are the results of running the top 400 repos with tsc comparing Something interesting changed - please have a look. Details
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@RyanCavanaugh Here are some more interesting changes from running the top 400 repos suite Details
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@RyanCavanaugh Here are some more interesting changes from running the top 400 repos suite Details
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Is it also time to make the message mention the flag? (I suspect it will be annoying to actually implement, though.) |
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It's easy to implement (just need to pass in the context to resolveExternalModuleName) Verbiage? |
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Honestly probably it's fine to not. We do need to fix the DT cases, though. Maybe the results mean that we should be ignoring these in declaration files? |
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Erroring in .d.ts files is still correct IMO, since if it's not yours it's almost certainly suppressed by skipLibCheck |
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#62442 doesn't seem to be going well
Fixes #62421