8000 New rule: use type parameter for .reduce instead of a cast · Issue #1604 · typescript-eslint/typescript-eslint · GitHub
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JoshuaKGoldberg opened this issue Feb 13, 2020 · 1 comment · Fixed by #1707
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New rule: use type parameter for .reduce instead of a cast #1604

JoshuaKGoldberg opened this issue Feb 13, 2020 · 1 comment · Fixed by #1707
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enhancement: new plugin rule New rule request for eslint-plugin has pr there is a PR raised to close this package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin

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@JoshuaKGoldberg
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JoshuaKGoldberg commented Feb 13, 2020 •
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Repro

const names = ['a', 'b'];

const record = names.reduce(
  (accum, name) => ({
    ...accum,
    [name]: true,
  }),
  {} as Record<string, boolean>
);

Expected Result

Typo! It should be Record<string, boolean>, but because we're using a cast, it's missed. Ah, this does fire a TS error, thanks - updated the sample.

Also, u Using a cast is unnecessary because Array#reduce can take in a type parameter indicating the default value & return type. The above code would be better written as:

const names = ['a', 'b'];

const record = names.reduce<Record<string, boolean>>(
  (accum, name) => ({
    ...accum,
    [name]: true,
  }),
  {} 
);

Actual Result

No error.

Versions

package version
@typescript-eslint/eslint-plugin 2.7.0
@typescript-eslint/parser 2.7.0
TypeScript 3.7.3
ESLint 5.15.1
node 12.4.0
npm 6.9.0
@JoshuaKGoldberg JoshuaKGoldberg added package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin triage Waiting for team members to take a look labels Feb 13, 2020
@bradzacher bradzacher added enhancement: new plugin rule New rule request for eslint-plugin and removed triage Waiting for team members to take a look labels Feb 13, 2020
@bradzacher
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Your example fires a TS error, so that does get caught.
image

Though I agree - I much prefer using the type parameter. Sounds like a good stylistic rule.

@G-Rath G-Rath mentioned this issue Mar 8, 2020
Merged
@bradzacher bradzacher added the has pr there is a PR raised to close this label Mar 8, 2020
@github-actions github-actions bot locked as resolved and limited conversation to collaborators May 14, 2020
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enhancement: new plugin rule New rule request for eslint-plugin has pr there is a PR raised to close this package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin
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feat(eslint-plugin): add rule prefer-reduce-type-parameter
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@JoshuaKGoldberg @bradzacher
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