feat(eslint-plugin): [no-useless-default-assignment] add rule #11720

ulrichstark · 2025-10-25T20:25:33Z

PR Checklist

Addresses an existing open issue: fixes Rule proposal: Detect useless default in function parameters and object destructuring #6106
That issue was marked as accepting prs
Steps in Contributing were taken

Overview

Reports useless default values.

function Bar({ foo = '' }: { foo: string }) {
  return foo;
}

const { foo = '' } = { foo: 'bar' };

const [foo = ''] = ['bar'];

[1, 2, 3].map((a = 42) => a + 1);

typescript-eslint · 2025-10-25T20:25:37Z

Thanks for the PR, @ulrichstark!

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 · 2025-10-25T20:27:25Z

View your CI Pipeline Execution ↗ for commit 026fd7f

Command	Status	Duration	Result
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`nx run-many -t lint`	✅ Succeeded	3m 15s	View ↗
`nx run-many -t typecheck`	✅ Succeeded	2m 1s	View ↗
`nx run types:build`	✅ Succeeded	1s	View ↗
`nx run integration-tests:test`	✅ Succeeded	6s	View ↗
`nx run generate-configs`	✅ Succeeded	8s	View ↗
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☁️ Nx Cloud last updated this comment at 2025-12-02 21:41:13 UTC

codecov · 2025-10-25T20:38:04Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.58%. Comparing base (5ac66a6) to head (026fd7f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11720      +/-   ##
==========================================
+ Coverage   90.53%   90.58%   +0.04%     
==========================================
  Files         523      524       +1     
  Lines       53097    53325     +228     
  Branches     8838     8892      +54     
==========================================
+ Hits        48074    48302     +228     
  Misses       5010     5010              
  Partials       13       13

Flag	Coverage Δ
unittest	`90.58% <100.00%> (+0.04%)`	⬆️

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

Files with missing lines	Coverage Δ
packages/eslint-plugin/src/configs/eslintrc/all.ts	`100.00% <100.00%> (ø)`
...lugin/src/configs/eslintrc/disable-type-checked.ts	`100.00% <100.00%> (ø)`
...n/src/configs/eslintrc/strict-type-checked-only.ts	`100.00% <100.00%> (ø)`
...plugin/src/configs/eslintrc/strict-type-checked.ts	`100.00% <100.00%> (ø)`
packages/eslint-plugin/src/configs/flat/all.ts	`100.00% <100.00%> (ø)`
...nt-plugin/src/configs/flat/disable-type-checked.ts	`100.00% <100.00%> (ø)`
...lugin/src/configs/flat/strict-type-checked-only.ts	`100.00% <100.00%> (ø)`
...int-plugin/src/configs/flat/strict-type-checked.ts	`100.00% <100.00%> (ø)`
...-plugin/src/rules/no-useless-default-assignment.ts	`100.00% <100.00%> (ø)`

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JoshuaKGoldberg

A great start, I love how readable this implementation is! 👏 nicely done.

Requesting changes mostly on getting test coverage up and covering edge cases. I suspect you'll have to tweak the implementation a little to deal with tuples. Cheers!

packages/eslint-plugin/docs/rules/no-useless-default-assignment.mdx

JoshuaKGoldberg · 2025-11-03T18:05:42Z

packages/eslint-plugin/src/rules/no-useless-default-assignment.ts

+        default:
+          return null;
+      }
+    }


[Non-Actionable] I'm surprised a utility doesn't already exist for this - but I couldn't find one.

getStaticValue: doesn't handle identifiers

getStringIfConstant: doesn't handle identifiers (it's a small wrapper around getStaticStringValue)

getStaticStringValue: didn't handle identifiers properly

Not requesting changes, just noting - maybe I missed one?

packages/eslint-plugin/tests/rules/no-useless-default-assignment.test.ts

packages/eslint-plugin/docs/rules/no-useless-default-assignment.mdx

packages/eslint-plugin/src/rules/no-useless-default-assignment.ts

packages/eslint-plugin/tests/docs.test.mts

…t.mdx Co-authored-by: Josh Goldberg ✨ <[email protected]>

…ignment]-add-rule

ulrichstark · 2025-11-04T16:37:30Z

Thanks Josh for your review! I already made all low effort changes. Do you also want me to turn the suggestion into a fix? I think it's safe in every case the project is properly typed.

JoshuaKGoldberg · 2025-11-04T16:52:49Z

Yes let's do that 🚀

ulrichstark · 2025-11-24T19:07:40Z

100% test coverage 🎉

JoshuaKGoldberg

Looking great, thanks for the coverage improvements! Just a couple points from me.

packages/eslint-plugin/docs/rules/no-useless-default-assignment.mdx

eslint.config.mjs

…ignment]-add-rule

JoshuaKGoldberg

Lovely work, thanks! 🙌

@ronami had a bunch of good points I'd missed last review cycle, so if they have time it'd be good to hear from them too.

ronami

🚀🚀 Looks amazing!

I've added two comments for bugs around destructuring records/mapped-types.

packages/eslint-plugin/src/rules/no-useless-default-assignment.ts

…ignment]-add-rule

ronami

Lovely work! 🏆

Requesting one final adjustment for records/mapped-types around the noUncheckedIndexedAccess compiler option.

packages/eslint-plugin/src/rules/no-useless-default-assignment.ts

ronami

🚀🚀

feat(eslint-plugin): [no-useless-default-assignment] add rule

a97e52e

ulrichstark added 5 commits October 25, 2025 22:58

support function parameters without type annotation

4a8ef6b

fix false positives

7637497

fixing more false positives

7a7b334

enable rule in repo to dogfood

527b367

cleanup code and increase code coverage

010c166

ulrichstark marked this pull request as draft October 25, 2025 22:13

cleanup code and add column numbers to tests

ff7bd0b

ulrichstark mentioned this pull request Oct 25, 2025

chore(eslint-plugin): use correct type for return type of createValidator #11721

Merged

3 tasks

add tests to increase test coverage

8d29d31

ulrichstark marked this pull request as ready for review October 25, 2025 22:59

JoshuaKGoldberg requested changes Nov 3, 2025

View reviewed changes

JoshuaKGoldberg added the awaiting response Issues waiting for a reply from the OP or another party label Nov 3, 2025

ulrichstark and others added 8 commits November 4, 2025 17:03

remove option allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing

df51d1c

remove comments at each test case

0526062

remove rule from rulesWithComplexOptionHeadings

90d121a

update snapshot

9b55fb2

Update packages/eslint-plugin/docs/rules/no-useless-default-assignmen…

422a704

…t.mdx Co-authored-by: Josh Goldberg ✨ <[email protected]>

Update packages/eslint-plugin/docs/rules/no-useless-default-assignmen…

16ff0d6

…t.mdx Co-authored-by: Josh Goldberg ✨ <[email protected]>

add rule to strict config

4c40bfb

Merge branch 'main' into feat(eslint-plugin)---no-useless-default-ass…

def0e8a

…ignment]-add-rule

ulrichstark added 3 commits November 5, 2025 20:11

turn suggestion into fix

6bef7fa

add more test cases and make them pass

299249e

make example code easier to understand and add tuple example

242883a

ulrichstark requested a review from JoshuaKGoldberg November 24, 2025 19:08

github-actions bot removed the awaiting response Issues waiting for a reply from the OP or another party label Nov 24, 2025

JoshuaKGoldberg previously approved these changes Nov 26, 2025

View reviewed changes

packages/eslint-plugin/docs/rules/no-useless-default-assignment.mdx Outdated Show resolved Hide resolved

eslint.config.mjs Outdated Show resolved Hide resolved

JoshuaKGoldberg requested review from bradzacher and ronami and removed request for ronami November 26, 2025 17:32

JoshuaKGoldberg added the 1 approval >=1 team member has approved this PR; we're now leaving it open for more reviews before we merge label Nov 26, 2025

github-actions bot removed the 1 approval >=1 team member has approved this PR; we're now leaving it open for more reviews before we merge label Nov 26, 2025

ulrichstark added 2 commits November 26, 2025 18:39

remove from eslint.config.mjs

37ce842

make "when not to use it" more relevant to this rule

33c859e

ulrichstark dismissed JoshuaKGoldberg’s stale review via 33c859e November 26, 2025 17:44

ulrichstark and others added 2 commits November 26, 2025 22:21

Merge branch 'main' into feat(eslint-plugin)---no-useless-default-ass…

052981c

…ignment]-add-rule

Merge branch 'main' into feat(eslint-plugin)---no-useless-default-ass…

3c04657

…ignment]-add-rule

JoshuaKGoldberg previously approved these changes Nov 28, 2025

View reviewed changes

JoshuaKGoldberg added the 1 approval >=1 team member has approved this PR; we're now leaving it open for more reviews before we merge label Nov 28, 2025

bradzacher previously approved these changes Nov 30, 2025

View reviewed changes

ronami reviewed Dec 1, 2025

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packages/eslint-plugin/src/rules/no-useless-default-assignment.ts Show resolved Hide resolved

packages/eslint-plugin/src/rules/no-useless-default-assignment.ts Show resolved Hide resolved

ulrichstark added 4 commits December 1, 2025 22:16

Merge branch 'main' into feat(eslint-plugin)---no-useless-default-ass…

071c2ef

…ignment]-add-rule

remove unnecessary type assertion

9334493

check for string index type

be81a7f

support compiler option noUncheckedIndexedAccess properly

ed0011c

ulrichstark dismissed stale reviews from bradzacher and JoshuaKGoldberg via ed0011c December 1, 2025 21:19

ulrichstark requested a review from ronami December 1, 2025 21:20

github-actions bot removed the 1 approval >=1 team member has approved this PR; we're now leaving it open for more reviews before we merge label Dec 1, 2025

ronami reviewed Dec 2, 2025

View reviewed changes

packages/eslint-plugin/src/rules/no-useless-default-assignment.ts Show resolved Hide resolved

also support noUncheckedIndexedAccess for records/mapped types

026fd7f

ulrichstark requested a review from ronami December 2, 2025 21:30

ronami approved these changes Dec 3, 2025

View reviewed changes

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feat(eslint-plugin): [no-useless-default-assignment] add rule #11720

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feat(eslint-plugin): [no-useless-default-assignment] add rule #11720

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