fix(eslint-plugin): [unified-signatures] compare type parameters by constraint instead of name by Arlikhozhaev · Pull Request #12741 · typescript-eslint/typescript-eslint

Arlikhozhaev · 2026-08-19T18:57:21Z

PR Checklist

Addresses an existing open issue: Bug: [unified-signatures] when using generic constraints, the name instead of the actual constraint is judged #12143
That issue was marked as accepting prs
Steps in Contributing were taken
If this PR used AI assistance, I followed the AI Contribution Policy

Overview

unified-signatures was comparing type parameter constraints by their AST node kind instead of the actual type.

That's why <T extends A> and <T extends B> were considered equal when both A and B were type references, even though they can represent different types.

This change reuses the existing typesAreEqual helper to compare the constraints instead, and removes the now unnecessary constraintsAreEqual helper.

This PR fixes the false positive described in #12143, where overloads with different type parameter constraints could be reported as combinable.

The other case in #12143 is <T extends string> vs <R extends string>. Those two can be combined, but the rule still compares type parameter names. To fix that we can match parameters by position, and you cannot simply rename T to R in the source text, because T might be a property name ({ T: string }).
That is a separate change, so this PR only fixes the extends A vs extends B false positive.

Added tests for type reference constraints and inline union constraints. The existing tests also continue to pass.

…raints by type, not node kind

typescript-eslint · 2026-08-19T18:57:23Z

Thanks for the PR, @Arlikhozhaev!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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nx-cloud · 2026-08-19T18:58:31Z

View your CI Pipeline Execution ↗ for commit 8c1a91c

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☁️ Nx Cloud last updated this comment at 2026-08-27 09:26:57 UTC

codecov · 2026-08-19T19:02:09Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.93%. Comparing base (e18fea8) to head (8c1a91c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12741      +/-   ##
==========================================
- Coverage   94.93%   94.93%   -0.01%     
==========================================
  Files         226      226              
  Lines       11539    11538       -1     
  Branches     3839     3838       -1     
==========================================
- Hits        10955    10954       -1     
  Misses        250      250              
  Partials      334      334

Flag	Coverage Δ
unittest	`94.93% <100.00%> (-0.01%)`	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ages/eslint-plugin/src/rules/unified-signatures.ts	`92.18% <100.00%> (-0.05%)`	⬇️

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
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StyleShit · 2026-08-20T05:58:06Z

Hey, please read our AI Contribution Policy and ensure your PR follows it.

Arlikhozhaev · 2026-08-20T07:34:59Z

I appreciate you pointing that out. I did use AI to help summarize the PR description, but I’ve rewritten it myself now. Also, I’ll keep this in mind for future PRs. Sorry about that.

I’m just getting started with open source, so I’d really appreciate any advice on how I can make sure I’m following the project’s expectations properly in future contributions.

I enjoy contributing here and would like to keep learning and improving.

StyleShit · 2026-08-20T17:50:59Z

Could you please also explain in the description why this is a partial fix?

Arlikhozhaev · 2026-08-20T19:51:40Z

Updated the PR description to explain why the <T> / <R> case is left out and why it requires a separate change.

…omparison

JoshuaKGoldberg

Nice and clean, thanks!

JoshuaKGoldberg · 2026-08-30T22:32:35Z

The existing tests also continue to pass.

Btw @Arlikhozhaev, it's pretty clear from your PR descriptions you're using AI to write them. They're not generally bad quality (some of the info & explanations have been quite helpful, thank you!) but they're quite verbose. Please be mindful that we have to read every single thing that comes our way - your PR descriptions, the much-lower-quality slop from other folks who're using AI, etc. It's draining. We'd appreciate it if you left out things that are self-evident - even if the AIs add them. ❤️

@Arlikhozhaev

| datasource | package | from | to | | ---------- | -------------------------------- | ------ | ------ | | npm | @typescript-eslint/eslint-plugin | 8.67.0 | 8.69.0 | | npm | @typescript-eslint/parser | 8.67.0 | 8.69.0 | ## [v8.69.0](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8690-2026-08-31) ##### 🚀 Features - **eslint-plugin:** \[no-misused-promises] add flagUnions option for checkConditionals ([#12603](typescript-eslint/typescript-eslint#12603)) ##### 🩹 Fixes - **eslint-plugin:** \[no-meaningless-void-operator] report void on non-call expressions ([#12727](typescript-eslint/typescript-eslint#12727)) - **eslint-plugin:** \[unified-signatures] compare type parameters by constraint instead of name ([#12741](typescript-eslint/typescript-eslint#12741)) - **eslint-plugin:** \[no-mixed-enums] use scope analysis instead of type checking for merged namespaces ([#12731](typescript-eslint/typescript-eslint#12731)) ##### ❤️ Thank You - Abdu Alim Arlikhozhaev [@Arlikhozhaev](https://github.com/Arlikhozhaev) - Evyatar Daud [@StyleShit](https://github.com/StyleShit) - Josh Goldberg ✨ - wonbeanie [@wonbeanie](https://github.com/wonbeanie) See [GitHub Releases](https://github.com/typescript-eslint/typescript-eslint/releases/tag/v8.69.0) for more information. You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website. ## [v8.68.0](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8680-2026-08-24) ##### 🚀 Features - **eslint-plugin:** \[strict-void-return] add fix suggestions ([#12086](typescript-eslint/typescript-eslint#12086)) ##### 🩹 Fixes - **eslint-plugin:** \[no-empty-object-type] ignore suggestions that result in invalid interfaces and export defaults ([#12739](typescript-eslint/typescript-eslint#12739)) - **eslint-plugin:** \[no-floating-promises] setting `ignoreVoid: false` results in false negative in ArrowFunctionExpression ([#12646](typescript-eslint/typescript-eslint#12646)) - **eslint-plugin:** \[no-unnecessary-type-assertion] prevent stack overflow in recursive types ([#12711](typescript-eslint/typescript-eslint#12711)) - **eslint-plugin:** \[unified-signatures] report identical signatures ([#12678](typescript-eslint/typescript-eslint#12678)) - **eslint-plugin:** \[return-await] prevent autofix from breaking code in arrow-functions ([#12707](typescript-eslint/typescript-eslint#12707)) - **eslint-plugin:** \[unified-signatures] deduplicate types in report ([#12656](typescript-eslint/typescript-eslint#12656)) ##### ❤️ Thank You - Evyatar Daud [@StyleShit](https://github.com/StyleShit) - Hugo [@hugop95](https://github.com/hugop95) - Niki [@phaux](https://github.com/phaux) - Younsang Na [@nayounsang](https://github.com/nayounsang) See [GitHub Releases](https://github.com/typescript-eslint/typescript-eslint/releases/tag/v8.68.0) for more information. You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website.

kirkwaiblinger · 2026-09-02T04:03:40Z

Btw @Arlikhozhaev, it's pretty clear from your PR descriptions you're using AI to write them.

In addition to JoshuaKGoldberg's comments, note that the the magic issue-closing string was removed from the issue template, so this wasn't linked to #12143 correctly.

Please follow our templates and processes 🙏

StyleShit · 2026-09-02T13:05:19Z

note that the the magic issue-closing string was removed from the issue template

I think it was intentional, as this only partially fixes it?
See the last part of the description:

The other case in #12143 is vs . Those two can be combined, but the rule still compares type parameter names. To fix that we can match parameters by position, and you cannot simply rename T to R in the source text, because T might be a property name ({ T: string }).
That is a separate change, so this PR only fixes the extends A vs extends B false positive.

kirkwaiblinger · 2026-09-02T13:54:34Z

Ah, my bad, then 👍

…26956) Port the `unified-signatures` changes from typescript-eslint/typescript-eslint#12656, typescript-eslint/typescript-eslint#12678, and typescript-eslint/typescript-eslint#12741: - Flatten and deduplicate union members in diagnostics, preserving necessary parentheses. - Report identical overload signatures. - Compare type parameter constraint text so distinct constraints such as `extends A` and `extends B` are not unified. Includes the upstream regressions and additional cases checked against ESLint 8.70.1. Parenthesized type nodes are unwrapped to match ESTree, while diagnostics retain Oxc's paired labels. The rule remains diagnostic-only. Validation: focused rule tests, all 62 TypeScript rule tests, and linter clippy passed. `just ready` passed the workspace check but could not finish the all-features test build: the linker ran out of disk space (`errno=28`).

fix(eslint-plugin): [unified-signatures] compare type parameter const…

7e5589d

…raints by type, not node kind

StyleShit added awaiting response Issues waiting for a reply from the OP or another party AI Slop Please read our AI contributor guidelines: https://typescript-eslint.io/contributing/ai-policy labels Aug 20, 2026

StyleShit removed awaiting response Issues waiting for a reply from the OP or another party AI Slop Please read our AI contributor guidelines: https://typescript-eslint.io/contributing/ai-policy labels Aug 23, 2026

StyleShit requested changes Aug 26, 2026

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Comment thread packages/eslint-plugin/src/rules/unified-signatures.ts

Comment thread packages/eslint-plugin/tests/rules/unified-signatures.test.ts Outdated

github-actions Bot added the awaiting response Issues waiting for a reply from the OP or another party label Aug 26, 2026

StyleShit changed the title ~~fix(eslint-plugin): [unified-signatures] compare type parameter constraints by type, not node kind~~ fix(eslint-plugin): [unified-signatures] compare type parameters by constraint instead of name Aug 26, 2026

test(eslint-plugin): [unified-signatures] cover type parameter name c…

8cd7f1d

…omparison

StyleShit approved these changes Aug 27, 2026

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StyleShit removed the awaiting response Issues waiting for a reply from the OP or another party label Aug 27, 2026

github-actions Bot added the 1 approval >=1 team member has approved this PR; we're now leaving it open for more reviews before we merge label Aug 27, 2026

Merge branch 'main' into fix/unified-signatures-constraint-comparison

8c1a91c

JoshuaKGoldberg approved these changes Aug 30, 2026

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JoshuaKGoldberg merged commit a2fccae into typescript-eslint:main Aug 30, 2026
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kirkwaiblinger linked an issue Sep 2, 2026 that may be closed by this pull request

Bug: [unified-signatures] when using generic constraints, the name instead of the actual constraint is judged #12143

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github-actions Bot mentioned this pull request Sep 18, 2026

chore(deps): update typescript-eslint monorepo to v8.69.0 victoraugustoas/finance-manager#136

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camc314 mentioned this pull request Sep 23, 2026

fix(linter/typescript/unified-signatures): align rule with upstream oxc-project/oxc#26956

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