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

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@ulrichstark ulrichstark commented Oct 25, 2025 •
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PR Checklist

Overview

Reports useless default values.

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

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

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

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typescript-eslint bot commented Oct 25, 2025

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.

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codecov bot commented Oct 25, 2025 •
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Codecov Report

❌ Patch coverage is 93.01075% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.67%. Comparing base (ea2ee6b) to head (def0e8a).

Files with missing lines Patch % Lines
...-plugin/src/rules/no-useless-default-assignment.ts 92.69% 13 Missing ⚠️
Additional details and impacted files 
@@           Coverage Diff            @@
##             main   #11720    +/-   ##
========================================
  Coverage   90.66%   90.67%            
========================================
  Files         518      519     +1     
  Lines       52435    52621   +186     
  Branches     8686     8721    +35     
========================================
+ Hits        47541    47714   +173     
- Misses       4880     4893    +13     
  Partials       14       14
Flag Coverage Δ
unittest 90.67% <93.01%> (+<0.01%) ⬆️

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 92.69% <92.69%> (ø)
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@ulrichstark ulrichstark marked this pull request as draft October 25, 2025 22:13
@ulrichstark ulrichstark mentioned this pull request Oct 25, 2025
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@ulrichstark ulrichstark marked this pull request as ready for review October 25, 2025 22:59
JoshuaKGoldberg
JoshuaKGoldberg requested changes Nov 3, 2025
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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/src/rules/no-useless-default-assignment.ts
default:
return null;
}
}
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@JoshuaKGoldberg JoshuaKGoldberg Nov 3, 2025

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[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
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[Testing] Some more "fun" cases to check:

Some of those already work, it'd just be good to have more unit tests for them to be safe.

@JoshuaKGoldberg JoshuaKGoldberg added the awaiting response Issues waiting for a reply from the OP or another party label Nov 3, 2025
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ulrichstark commented Nov 4, 2025

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.

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JoshuaKGoldberg commented Nov 4, 2025

Yes let's do that 🚀

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Rule proposal: Detect useless default in function parameters and object destructuring

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