10000 Bug: [no-empty-object-type] false positive/incorrect fixes for default type parameter · Issue #9761 · typescript-eslint/typescript-eslint · GitHub
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Bug: [no-empty-object-type] false positive/incorrect fixes for default type parameter #9761

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printfn opened this issue Aug 9, 2024 · 8 comments
Closed
4 tasks done

Bug: [no-empty-object-type] false positive/incorrect fixes for default type parameter #9761

printfn opened this issue Aug 9, 2024 · 8 comments
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bug Something isn't working locked due to age Please open a new issue if you'd like to say more. See https://typescript-eslint.io/contributing. package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin working as intended Issues that are closed as they are working as intended

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@printfn
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printfn commented Aug 9, 2024

Before You File a Bug Report Please Confirm You Have Done The Following...

  • I have tried restarting my IDE and the issue persists.
  • I have updated to the latest version of the packages.
  • I have searched for related issues and found none that matched my issue.
  • I have read the FAQ and my problem is not listed.

Playground Link

https://typescript-eslint.io/play/#ts=5.5.2&fileType=.tsx&code=KYDwDg9gTgLgBASwHY2FAZgQwMbDgSQB4AFOUVJAEwGc4AlYbaSw6mKZAcwBo42OknAHxwAvHADeAXxESAsACg4cMJiiYAttQBccYgG5FUoA&eslintrc=N4KABGBEBOCuA2BTAzpAXGUEKQAIBcBPABxQGNoBLY-AWhXkoDt8B6Jge3oFsbDaOAIwBWiMnSKl0URNGgdokcGAC%2BIFUA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eFYDAruuGAL4g9A&tokens=false

Repro Code

export interface I<P extends Record<string, string> = {}> {
  params: P;
}

ESLint Config

{
  "rules": {
    "@typescript-eslint/no-empty-object-type": "error"
  }
}

tsconfig

{
  "compilerOptions": {
    // ...
  }
}

Expected Result

I'm not sure this should even produce an error. Neither of the suggested fixes works.

Actual Result

The {} ("empty object") type allows any non-nullish value, including literals like 0 and "".

  • If that's what you want, disable this lint rule with an inline comment or configure the 'allowObjectTypes' rule option.
  • If you want a type meaning "any object", you probably want object instead.
  • If you want a type meaning "any value", you probably want unknown instead. 5:55 - 5:57

Replace {} with object.
Replace {} with unknown.

Additional Info

No response
@printfn printfn added bug Something isn't working package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin triage Waiting for team members to take a look labels Aug 9, 2024
@Josh-Cena
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Josh-Cena commented Aug 9, 2024 •
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The suggestions are there for common cases; neither of them are equivalent to {} and we don't guarantee that your code continues to work. In this case, the report is expected because it may result in unexpected behaviors:

export interface I<P extends Record<string, string> = {}> {
  params: P;
}

const x: I = { params: 1 }; // Allowed

You can use P extends Record<string, string> = Record<string, string> as the default, or P extends Record<string, string> = Record<string, never> if you want the default to not contain any properties, or even just disable the rule here, if you know what you are writing is intended.

@bradzacher
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Yeah this reporting is entirely correct and using {} here is unsafe as Josh mentions.
The suggestions are exactly that - suggestions. They aren't automatically applied and must be manually evaluated and manually applied.

In this case Josh's suggestion is correct - you have a generic constraint, so use the constraint as the default. Though you probably want something like Record<string, never> which would force it to be an empty object and accept { params: {} } and reject { params: 1 } and { params: { prop: 1 } }.

@typescript-eslint/triage-team -- what do we think about adding a suggestion here:
If we detect that the {} is used as a generic default AND the generic has a constraint, then we additionally suggest the constraint as a special case suggestion

@bradzacher bradzacher added working as intended Issues that are closed as they are working as intended and removed triage Waiting for team members to take a look labels Aug 9, 2024
@Josh-Cena
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Hmmm, negative—I don't think that is going to help in most cases and really complicates the code.

@kirkwaiblinger
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-1 from me, too, I'd rather avoid blessing Record<string, never> with a typescript-eslint suggestion (see also #8977 (comment) and microsoft/TypeScript#57735 (comment))

@bradzacher
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bradzacher commented Aug 9, 2024 •
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I meant specifically if the code is of the form <T extends U = {}>
Then we would additionally suggest replacing {} with U (i.e. <T extends U = U>)
So in this case the additional suggestion would suggest Record<string, string> (i.e. <P extends Record<string, string> = Record<string, string>>)

@Josh-Cena
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Yeah, I meant—this is not always, if ever, going to be what the user intends, and only solves a handful of cases out-of-the-box.

@kirkwaiblinger
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Oh, I misunderstood, thanks for clarifying. +/- 0 from me on this 🤷‍♂️

@bradzacher
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Okay then it seems like we're in agreement - this is working as intended and no changes shall be made.

@bradzacher bradzacher closed this as not planned Won't fix, can't repro, duplicate, stale Aug 9, 2024
@github-actions github-actions bot added the locked due to age Please open a new issue if you'd like to say more. See https://typescript-eslint.io/contributing. label Aug 17, 2024
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