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Overview

The no-unnecessary-type-conversion rule was incorrectly reporting violations when .toString() was called on enum members. While enums may be string-like or number-like under the hood, they are conceptually opaque types in TypeScript.

The rule now skips reporting for enum types and enum members by checking their type and symbol flags. This prevents false positives where calling .toString() is valid and sometimes necessary, and avoids conflicts with no-unsafe-enum-comparison

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Thanks for the PR, @thebolarin!

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☁️ Nx Cloud last updated this comment at 2025-09-09 22:56:27 UTC

@thebolarin thebolarin changed the title fix: enums in no-unnecessary-type-conversion fix(eslint-plugin): enums in no-unnecessary-type-conversion Aug 17, 2025
@thebolarin thebolarin force-pushed the fix/no-unnecessary-type-conversion-enum branch from 02c5652 to 566410b Compare August 18, 2025 18:43
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.90%. Comparing base (70c948c) to head (416b38d).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files
@@           Coverage Diff           @@
##             main   #11490   +/-   ##
=======================================
  Coverage   90.90%   90.90%           
=======================================
  Files         505      505           
  Lines       51208    51221   +13     
  Branches     8441     8445    +4     
=======================================
+ Hits        46551    46564   +13     
  Misses       4644     4644           
  Partials       13       13           
Flag Coverage Δ
unittest 90.90% <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
...plugin/src/rules/no-unnecessary-type-conversion.ts 100.00% <100.00%> (ø)
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@bradzacher bradzacher changed the title fix(eslint-plugin): enums in no-unnecessary-type-conversion fix(eslint-plugin): [no-unnecessary-type-conversion] ignore enum members Aug 18, 2025
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thanks!

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/home/runner/work/typescript-eslint/typescript-eslint/packages/eslint-plugin/src/rules/no-unnecessary-type-conversion.ts
  27:12  error  Unnecessary conditional, expected left-hand side of `??` operator to be possibly null or undefined  @typescript-eslint/no-unnecessary-condition
  27:12  error  Do not use Type.symbol because it is poorly typed. Use Type.getSymbol() instead                     @typescript-eslint/internal/no-poorly-typed-ts-props
  27:23  error  Unnecessary optional chain on a non-nullish value                                                   @typescript-eslint/no-unnecessary-condition

there are some lint errors to fix

@bradzacher bradzacher added the awaiting response Issues waiting for a reply from the OP or another party label Aug 18, 2025
@thebolarin thebolarin force-pushed the fix/no-unnecessary-type-conversion-enum branch from ac38a26 to 1391151 Compare August 18, 2025 23:10
@thebolarin thebolarin force-pushed the fix/no-unnecessary-type-conversion-enum branch from 1391151 to be5ba37 Compare August 18, 2025 23:27
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thebolarin commented Aug 18, 2025

/home/runner/work/typescript-eslint/typescript-eslint/packages/eslint-plugin/src/rules/no-unnecessary-type-conversion.ts
  27:12  error  Unnecessary conditional, expected left-hand side of `??` operator to be possibly null or undefined  @typescript-eslint/no-unnecessary-condition
  27:12  error  Do not use Type.symbol because it is poorly typed. Use Type.getSymbol() instead                     @typescript-eslint/internal/no-poorly-typed-ts-props
  27:23  error  Unnecessary optional chain on a non-nullish value                                                   @typescript-eslint/no-unnecessary-condition

there are some lint errors to fix

@bradzacher Thanks for the review. I have pushed some changes to fix that

@thebolarin thebolarin force-pushed the fix/no-unnecessary-type-conversion-enum branch from be5ba37 to 5fc90c4 Compare August 19, 2025 08:37
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should the same fix be applied in no-unnecessary-template-expression?

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@bradzacher Could you please take a look at this PR when you have a chance? Thanks!

@bradzacher bradzacher self-requested a review September 1, 2025 20:01
@github-actions github-actions bot removed the awaiting response Issues waiting for a reply from the OP or another party label Sep 1, 2025
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🎇 thanks!

@JoshuaKGoldberg JoshuaKGoldberg merged commit 2ed6857 into typescript-eslint:main Sep 15, 2025
61 of 62 checks passed
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should the same fix be applied in no-unnecessary-template-expression?

@skondrashov if you've got a repro, we'd happily take an issue.

ArnaudBarre added a commit to ArnaudBarre/tsl that referenced this pull request Sep 16, 2025
renovate bot added a commit to andrei-picus-tink/auto-renovate that referenced this pull request Sep 17, 2025
| datasource | package                          | from   | to     |
| ---------- | -------------------------------- | ------ | ------ |
| npm        | @typescript-eslint/eslint-plugin | 8.43.0 | 8.44.0 |
| npm        | @typescript-eslint/parser        | 8.43.0 | 8.44.0 |


## [v8.44.0](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8440-2025-09-15)

##### 🚀 Features

- **eslint-plugin:** \[await-thenable] report invalid (non-promise) values passed to promise aggregator methods ([#11267](typescript-eslint/typescript-eslint#11267))

##### 🩹 Fixes

- **eslint-plugin:** \[no-unnecessary-type-conversion] ignore enum members ([#11490](typescript-eslint/typescript-eslint#11490))

##### ❤️ Thank You

- Moses Odutusin [@thebolarin](https://github.com/thebolarin)
- Ronen Amiel

You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website.
renovate bot added a commit to andrei-picus-tink/auto-renovate that referenced this pull request Sep 17, 2025
| datasource | package                          | from   | to     |
| ---------- | -------------------------------- | ------ | ------ |
| npm        | @typescript-eslint/eslint-plugin | 8.43.0 | 8.44.0 |
| npm        | @typescript-eslint/parser        | 8.43.0 | 8.44.0 |


## [v8.44.0](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8440-2025-09-15)

##### 🚀 Features

- **eslint-plugin:** \[await-thenable] report invalid (non-promise) values passed to promise aggregator methods ([#11267](typescript-eslint/typescript-eslint#11267))

##### 🩹 Fixes

- **eslint-plugin:** \[no-unnecessary-type-conversion] ignore enum members ([#11490](typescript-eslint/typescript-eslint#11490))

##### ❤️ Thank You

- Moses Odutusin [@thebolarin](https://github.com/thebolarin)
- Ronen Amiel

You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website.
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Bug: [no-unnecessary-type-conversion] rule reports on enum types which should be treated as opaque

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