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Merged
JoshuaKGoldberg merged 5 commits into from
Dec 17, 2025
Merged

fix(eslint-plugin): [no-unnecessary-type-assertion] correct handling of undefined vs. void #11826

JoshuaKGoldberg merged 5 commits into from
Dec 17, 2025
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@Tamashoo
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@Tamashoo Tamashoo commented Dec 7, 2025 •
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PR Checklist

Overview

Added special handling for type checking of IIFEs in the no-unnecessary-type-assertion rule.
Introduced an isIIFE type guard and a getUncastType helper function to correctly resolve IIFE return types, converting implicit undefined to void for functions without explicit return type annotations.
This improves the accuracy of unnecessary assertion detection for IIFE expressions.

@Tamashoo
fix(eslint-plugin): [no-unnecessary-type-assertion] enhance type asse…
2dce35a 
…rtion handling for IIFE and add related tests
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typescript-eslint bot commented Dec 7, 2025

Thanks for the PR, @Tamashoo!

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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View your CI Pipeline Execution ↗ for commit 929ad00

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nx test eslint-plugin --coverage=false ✅ Succeeded 5m 17s View ↗
nx run-many -t lint ✅ Succeeded 3m 18s View ↗
nx run-many -t typecheck ✅ Succeeded 1m 57s View ↗
nx test eslint-plugin-internal --coverage=false ✅ Succeeded 3s View ↗
nx test typescript-estree --coverage=false ✅ Succeeded 2s View ↗
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☁️ Nx Cloud last updated this comment at 2025-12-16 14:41:05 UTC

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codecov bot commented Dec 7, 2025 •
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.59%. Comparing base (32b7e89) to head (929ad00).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files 
@@            Coverage Diff             @@
##             main   #11826      +/-   ##
==========================================
+ Coverage   90.53%   90.59%   +0.05%     
==========================================
  Files         523      524       +1     
  Lines       53096    53410     +314     
  Branches     8838     8918      +80     
==========================================
+ Hits        48073    48385     +312     
- Misses       5010     5012       +2     
  Partials       13       13
Flag Coverage Δ
unittest 90.59% <100.00%> (+0.05%) ⬆️

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

Files with missing lines Coverage Δ
...-plugin/src/rules/no-unnecessary-type-assertion.ts 98.24% <100.00%> (+0.15%) ⬆️

... and 11 files with indirect coverage changes

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JoshuaKGoldberg
JoshuaKGoldberg requested changes Dec 14, 2025
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This is looking good, thanks for the PR! I poked at the rule in a bunch of different ways and couldn't figure out amy way to break the new implementation. Nice work 🙂.

Just requesting changes on more thorough testing. This area of TypeScript (inferred types, overloads/signatures) tends to cause bugs in lint rules a lot.

@JoshuaKGoldberg JoshuaKGoldberg added the awaiting response Issues waiting for a reply from the OP or another party label Dec 14, 2025
@Tamashoo
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Tamashoo commented Dec 15, 2025

@JoshuaKGoldberg
Thank you for the review!

I’ve added the minimal test cases you suggested and fixed the existing tests.
I’m planning to add an additional test that involves generics before re-requesting review.

If you have any further thoughts on edge cases worth covering, please let me know.
Thank you!

@Tamashoo
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Tamashoo commented Dec 16, 2025 •
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I added test cases for overloaded and union return types in 2b0b517.
I also added additional cases covering both generics and overloads in 18316e1, with some minor fixes.

@github-actions github-actions bot removed the awaiting response Issues waiting for a reply from the OP or another party label Dec 16, 2025
JoshuaKGoldberg
JoshuaKGoldberg approved these changes Dec 17, 2025
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🙌 wonderful, thanks!

@JoshuaKGoldberg 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 Dec 17, 2025
@JoshuaKGoldberg JoshuaKGoldberg changed the title fix(eslint-plugin): [no-unnecessary-type-assertion] enhance type assertion handling for IIFE fix(eslint-plugin): [no-unnecessary-type-assertion] correct handling of undefined vs. void Dec 17, 2025
@JoshuaKGoldberg JoshuaKGoldberg merged commit 46171f0 into typescript-eslint:main Dec 17, 2025
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Bug: [no-unnecessary-type-assertion] false positive when casting IIFE with void return type to undefined

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@Tamashoo @JoshuaKGoldberg