feat(eslint-plugin): Add BigInt object type to default ban-types list

[tduyduc]

PR Checklist

• Addresses an existing open issue: fixes #000 No issues have been created about this feature
• That issue was marked as accepting prs No issues have been created about this feature
• Steps in CONTRIBUTING.md were taken

Overview

The pull request title says it all: to add BigInt type to the default list of banned types, given that bigint is a primitive type (just like boolean, string, number, and symbol).

The ban-types rule source code and the rule documentation have been changed.

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[typescript-eslint]

Thanks for the PR, @tduyduc!

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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[codecov]

Codecov Report

Merging #4970 (bb7f97a) into main (77e15a9) will increase coverage by 1.61%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #4970      +/-   ##
==========================================
+ Coverage   92.64%   94.25%   +1.61%     
==========================================
  Files         190      153      -37     
  Lines       10251     8305    -1946     
  Branches     3249     2702     -547     
==========================================
- Hits         9497     7828    -1669     
+ Misses        502      263     -239     
+ Partials      252      214      -38     

Flag	Coverage Δ
unittest	94.25% <ø> (+1.61%)	⬆️

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

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/array-type.ts	97.18% <ø> (ø)
packages/eslint-plugin/src/rules/ban-types.ts	100.00% <ø> (ø)
packages/type-utils/src/getTypeName.ts
...escript-estree/src/semantic-or-syntactic-errors.ts
packages/type-utils/src/getSourceFileOfNode.ts
packages/typescript-estree/src/simple-traverse.ts
packages/typescript-estree/src/ast-converter.ts
packages/typescript-estree/src/node-utils.ts
...internal/src/rules/no-typescript-default-import.ts
...ges/type-utils/src/getConstrainedTypeAtLocation.ts
... and 29 more

[Josh-Cena]

It is impossible to construct a wrapper object of type BigInt, so BigInt and bigint are literally the same type, contrary to number or boolean.

[bradzacher]

99.99999% of the time you don't want the capital version of the type, nor should you be constructing a wrapper object. Which is why the rule points people at using the lowercase type for the primitives.

[Josh-Cena]

Ugh, I see we ban Symbol as well, even when there's no danger. I see the reasoning.

[JoshuaKGoldberg]

Yup this makes sense, thanks!

[tduyduc]

It is impossible to construct a wrapper object of type BigInt, so BigInt and bigint are literally the same type, contrary to number or boolean.

Boxed objects of symbols and bigints cannot be instantiated via new Symbol() or new BigInt(1n), but can via Object(Symbol()) and Object(1n) explicitly. Of course we won't need them generally all the time.

99.99999% of the time you don't want the capital version of the type, nor should you be constructing a wrapper object. Which is why the rule points people at using the lowercase type for the primitives.

It is also worth noting that the boxed primitive types can screw up TypeScript type guards. This can be a problem should we face bigger unions of types.

declare var x: BigInt | bigint | undefined;
if (x instanceof Object) {
  x; // is BigInt (object)
} else if (typeof x === 'bigint') {
  x; // is bigint (primitive)
}

[Josh-Cena]

Oh I wasn't aware of the narrowing issue. It makes much more sense then 👍