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fix(typescript-eslint): export plugin, parser, and configs that are compatible with both defineConfig() and tseslint.config() #11475

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merged 2 commits into from
Aug 16, 2025
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fix(typescript-eslint): export plugin, parser, and configs that are compatible with both defineConfig() and tseslint.config() #11475

merged 2 commits into from
Aug 16, 2025
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kirkwaiblinger
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@kirkwaiblinger kirkwaiblinger commented Aug 13, 2025 •
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Third time's the charm 🙃

I realized that, if we're extremely vague about what the parser, plugin, and configs are, we can easily satisfy both the expected types from defineConfig() and tseslint.config(), without running into the many incompatibilities I experienced during previous attempts. While this sacrifices precision, the exact shapes of those objects aren't actually important at all to users; it's only important that they be usable within their configs. So, I think this is a worthwhile tradeoff.

It's possible that some plugin authors, or downstream consumers that use our tools in some way other than in their lint configuration might experience some type errors as a result of this. Fixing these errors should be quite simple, since one can use type assertions to get the previous (also quite vague) types:

tseslint.parser as FlatConfig.Parser;
tseslint.plugin as FlatConfig.Plugin;
tseslint.configs['foo'] as FlatConfig.Config | FlatConfig.ConfigArray

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Thanks for the PR, @kirkwaiblinger!

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Thanks again!

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@thernstig
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Shouldn't this also be updated?

typescript-eslint/docs/getting-started/Quickstart.mdx

Lines 54 to 63 in b2ee794

<details>
<summary>Aside on ESLint's `defineConfig()`</summary>
ESLint also provides a `defineConfig()` helper similar to `tseslint.config()`.
However, there is a types incompatibility issue that causes type errors to incorrectly be reported when mixing typescript-eslint's configs and `defineConfig()`.
For now we recommend using `tseslint.config()` for use with typescript-eslint's configs.
See [typescript-eslint#10899](https://github.com/typescript-eslint/typescript-eslint/issues/10899) for more details.
</details>

Along with the example on that same page to start using defineConfig instead?

@kirkwaiblinger
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@thernstig

Shouldn't this also be updated?

typescript-eslint/docs/getting-started/Quickstart.mdx

Lines 54 to 63 in b2ee794

<details>
<summary>Aside on ESLint's `defineConfig()`</summary>
ESLint also provides a `defineConfig()` helper similar to `tseslint.config()`.
However, there is a types incompatibility issue that causes type errors to incorrectly be reported when mixing typescript-eslint's configs and `defineConfig()`.
For now we recommend using `tseslint.config()` for use with typescript-eslint's configs.
See [typescript-eslint#10899](https://github.com/typescript-eslint/typescript-eslint/issues/10899) for more details.
</details>

Possibly could... Though in the name of caution it might be worth releasing the types change and waiting a week to make sure it's doesn't end up messing up people's configs too before we take down the notice. Could go either way.

Along with the example on that same page to start using defineConfig instead?

This will for sure not happen as part of this PR, but endorsing defineConfig()is tracked separately as #10935

bradzacher
bradzacher approved these changes Aug 16, 2025
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packages/typescript-eslint/tests/type-compatibility.test-d.ts
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is test-d.ts run by vitest? TIL

@bradzacher bradzacher merged commit 3426f0d into typescript-eslint:main Aug 16, 2025
114 of 121 checks passed
@kirkwaiblinger kirkwaiblinger deleted the fix-define-config-incompatibility branch August 16, 2025 04:12
@Martinspire
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If another way of configuring the project is supported, shouldn't the overall readme have a way to do this? I mean, if you want people to start using it, it would be nice to know how it works...

@thernstig
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If another way of configuring the project is supported, shouldn't the overall readme have a way to do this? I mean, if you want people to start using it, it would be nice to know how it works...

See #10935

This was referenced Aug 19, 2025
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Bug: typescript-eslint config types are incompatible with defineConfig() types
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@kirkwaiblinger @thernstig @Martinspire @bradzacher