fix(eslint-plugin): [prefer-reduce-type-parameter] don't report cases in which the fix results in a type error #10494

ronami · 2024-12-13T09:44:45Z

PR Checklist

Addresses an existing open issue: fixes Bug: [prefer-reduce-type-parameter] unfixable reporting #3440
That issue was marked as accepting prs
Steps in Contributing were taken

Overview

This PR tackles #3440 and makes the rule skip cases where the type assertion is necessary and auto-fixing to using reduce()'s type parameter will result in a type error.

Alternatively, as code that does this isn't exactly safe, the rule can still report such cases but use a suggestion instead of an auto-fix (although no-unsafe-type-assertion will report the assertion as unsafe).

typescript-eslint · 2024-12-13T09:44:48Z

Thanks for the PR, @ronami!

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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ronami · 2024-12-13T09:57:32Z

packages/eslint-plugin/tests/rules/prefer-reduce-type-parameter.test.ts

+      function f<T extends Record<string, boolean>>() {
+        ['a', 'b'].reduce(
+          (accum, name) => ({
+            ...accum,
+            [name]: true,
+          }),
+          {} as T,
+        );
+      }


This was a missing edge case in #10453.

ronami · 2024-12-13T09:59:38Z

packages/eslint-plugin/tests/rules/prefer-reduce-type-parameter.test.ts

+      ['a', 'b'].reduce(
+        (accum, name) => ({
+          ...accum,
+          [name]: true,
+        }),
+        { a: true, b: false, c: true } as Record<'a' | 'b', boolean>,
+      );


I'm not sure if it's necessary to cover this, but it's somewhat of an edge case with TypeScript's assignability.

Heh, yeah, I say let's cover it.

codecov · 2024-12-13T10:01:37Z

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.78%. Comparing base (a383d50) to head (505f513).

❗ Current head 505f513 differs from pull request most recent head 906407e

Please upload reports for the commit 906407e to get more accurate results.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10494   +/-   ##
=======================================
  Coverage   86.78%   86.78%           
=======================================
  Files         445      445           
  Lines       15356    15363    +7     
  Branches     4472     4474    +2     
=======================================
+ Hits        13326    13333    +7     
  Misses       1675     1675           
  Partials      355      355

Flag	Coverage Δ
unittest	`86.78% <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
...t-plugin/src/rules/prefer-reduce-type-parameter.ts	`100.00% <100.00%> (ø)`

ronami · 2024-12-13T10:12:13Z

packages/eslint-plugin/tests/rules/prefer-reduce-type-parameter.test.ts

+      }
+    `,
+    `
+      ['a', 'b'].reduce((accum, name) => \`\${accum} | hello \${name}!\`);


This isn't directly related to the change, but it was previously missing coverage, and because it is on its own line now, it fails codecov.

…ting

JoshuaKGoldberg

YES FINALLY!!!!

@controversial

| datasource | package | from | to | | ---------- | -------------------------------- | ------ | ------ | | npm | @typescript-eslint/eslint-plugin | 8.18.1 | 8.18.2 | | npm | @typescript-eslint/parser | 8.18.1 | 8.18.2 | ## [v8.18.2](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8182-2024-12-23) ##### 🩹 Fixes - **eslint-plugin:** \[no-unnecessary-condition] handle noUncheckedIndexedAccess true ([#10514](typescript-eslint/typescript-eslint#10514)) - **eslint-plugin:** \[consistent-type-assertions] allow default assertionStyle option ([#10512](typescript-eslint/typescript-eslint#10512)) - **eslint-plugin:** \[no-unnecessary-type-arguments] handle type/value context ([#10503](typescript-eslint/typescript-eslint#10503)) - **eslint-plugin:** \[no-unsafe-type-assertion] fix for unsafe assertion to a constrained type parameter ([#10461](typescript-eslint/typescript-eslint#10461)) - **eslint-plugin:** \[consistent-indexed-object-style] use a suggestion over an auto-fix if can't reliably determine that produced index signature is valid ([#10490](typescript-eslint/typescript-eslint#10490)) - **eslint-plugin:** \[no-unnecessary-condition] don't flag values of an unconstrained or valid type parameter ([#10473](typescript-eslint/typescript-eslint#10473)) - **eslint-plugin:** \[prefer-reduce-type-parameter] don't report cases in which the fix results in a type error ([#10494](typescript-eslint/typescript-eslint#10494)) - **eslint-plugin:** \[no-deprecated] not reporting usages of deprecated declared constants as object value ([#10498](typescript-eslint/typescript-eslint#10498)) ##### ❤️ Thank You - Luke Deen Taylor [@controversial](https://github.com/controversial) - Ronen Amiel - Scott O'Hara - YeonJuan [@yeonjuan](https://github.com/yeonjuan) - Yukihiro Hasegawa [@y-hsgw](https://github.com/y-hsgw) You can read about our [versioning strategy](https://main--typescript-eslint.netlify.app/users/versioning) and [releases](https://main--typescript-eslint.netlify.app/users/releases) on our website.

@controversial

##### [v8.18.2](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8182-2024-12-23) ##### 🩹 Fixes - **eslint-plugin:** \[no-unnecessary-condition] handle noUncheckedIndexedAccess true ([#10514](typescript-eslint/typescript-eslint#10514)) - **eslint-plugin:** \[consistent-type-assertions] allow default assertionStyle option ([#10512](typescript-eslint/typescript-eslint#10512)) - **eslint-plugin:** \[no-unnecessary-type-arguments] handle type/value context ([#10503](typescript-eslint/typescript-eslint#10503)) - **eslint-plugin:** \[no-unsafe-type-assertion] fix for unsafe assertion to a constrained type parameter ([#10461](typescript-eslint/typescript-eslint#10461)) - **eslint-plugin:** \[consistent-indexed-object-style] use a suggestion over an auto-fix if can't reliably determine that produced index signature is valid ([#10490](typescript-eslint/typescript-eslint#10490)) - **eslint-plugin:** \[no-unnecessary-condition] don't flag values of an unconstrained or valid type parameter ([#10473](typescript-eslint/typescript-eslint#10473)) - **eslint-plugin:** \[prefer-reduce-type-parameter] don't report cases in which the fix results in a type error ([#10494](typescript-eslint/typescript-eslint#10494)) - **eslint-plugin:** \[no-deprecated] not reporting usages of deprecated declared constants as object value ([#10498](typescript-eslint/typescript-eslint#10498)) ##### ❤️ Thank You - Luke Deen Taylor [@controversial](https://github.com/controversial) - Ronen Amiel - Scott O'Hara - YeonJuan [@yeonjuan](https://github.com/yeonjuan) - Yukihiro Hasegawa [@y-hsgw](https://github.com/y-hsgw) You can read about our [versioning strategy](https://main--typescript-eslint.netlify.app/users/versioning) and [releases](https://main--typescript-eslint.netlify.app/users/releases) on our website.

initial implementation

e526696

ronami commented Dec 13, 2024

View reviewed changes

ronami marked this pull request as ready for review December 13, 2024 10:01

ronami marked this pull request as draft December 13, 2024 10:01

cover a missing test

525a109

ronami commented Dec 13, 2024

View reviewed changes

ronami marked this pull request as ready for review December 13, 2024 10:29

ronami added 2 commits December 13, 2024 13:05

Merge branch 'main' into prefer-reduce-type-parameter-unfixable-repor…

505f513

…ting

change comment wording

906407e

JoshuaKGoldberg approved these changes Dec 14, 2024

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 Dec 14, 2024

JoshuaKGoldberg merged commit ba39dde into typescript-eslint:main Dec 21, 2024
62 checks passed

ronami deleted the prefer-reduce-type-parameter-unfixable-reporting branch December 21, 2024 14:09

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fix(eslint-plugin): [prefer-reduce-type-parameter] don't report cases in which the fix results in a type error #10494

fix(eslint-plugin): [prefer-reduce-type-parameter] don't report cases in which the fix results in a type error #10494

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fix(eslint-plugin): [prefer-reduce-type-parameter] don't report cases in which the fix results in a type error #10494

fix(eslint-plugin): [prefer-reduce-type-parameter] don't report cases in which the fix results in a type error #10494

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