feat(eslint-plugin): [no-type-alias]: add allowGenerics option

[scottohara]

Fixes #3784

(⚠️ Note: an earlier version of this PR introduced an allowedAliasNames: [] option which accepted an array of strings to ignore. This was later swapped to an allowGenerics: 'always' | 'never' option that permits/prevents any TSTypeReference that has parameters)

This change adds an option to no-type-alias to allow generics to be ignored by the rule.

The new option is allowGenerics, and can be set to "always" or "never" (default is "never"), e.g.

{
  "@typescript-eslint/no-type-alias": ["error", { "allowGenerics": "always" }]
}

As discussed in #3784, the main driver for this change is to avoid a conflict when using both consistent-indexed-object-style and no-type-alias with their default options.

Specifically to allow the following code to pass both rules:

type Foo = Record<string, number>;

[typescript-eslint]

Thanks for the PR, @scottohara!

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 #3865 (e862229) into master (4a88de2) will increase coverage by 0.83%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3865      +/-   ##
==========================================
+ Coverage   92.70%   93.53%   +0.83%     
==========================================
  Files         329      149     -180     
  Lines       11534     8049    -3485     
  Branches     3257     2553     -704     
==========================================
- Hits        10693     7529    -3164     
+ Misses        368      164     -204     
+ Partials      473      356     -117     

Flag	Coverage Δ
unittest	93.53% <100.00%> (+0.83%)	⬆️

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

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/no-type-alias.ts	100.00% <100.00%> (ø)
...tal-utils/src/ast-utils/eslint-utils/predicates.ts
packages/typescript-estree/src/node-utils.ts
packages/scope-manager/src/lib/es2018.intl.ts
packages/scope-manager/src/lib/es2015.symbol.ts
...ages/scope-manager/src/referencer/ExportVisitor.ts
packages/scope-manager/src/lib/es2016.full.ts
packages/scope-manager/src/lib/es2019.string.ts
packages/scope-manager/src/scope/TSModuleScope.ts
packages/scope-manager/src/lib/es2019.symbol.ts
... and 171 more

[JounQin]

I think an optionallowGeneric could cover these usages automatically?

[scottohara]

Hi @JounQin,

Thanks for your suggestion of allowGeneric and for the pointer to #3181 (which I apologise I had not previously seen).

I think I agree with you that an allowGeneric option would be a simpler & cleaner solution than the allowedAliasNames one in this PR.

To confirm, for declarations like:

type Foo = Record<string, number>;
type Bar = Readonly<Foo>;
// etc.

...the allowGeneric option would permit any TSTypeAliasDeclaration where:

1. typeAnnotation.type === AST_NODE_TYPES.TSTypeReference and
2. typeAnnotation.typeParameters !== undefined

I'm interested to understand whether the option also needs to support some of the other elements of your no-restricted-syntax selector such as

• .typeAnnotation[type=/^TS.*Keyword$/]
• :not(:has(TSQualifiedName))

?

Are there any other forms of generic declarations (other than TSTypeReference) that we need to cater for?

[JounQin]

@scottohara Personally I'd love to see an option to cover my use case which only disallows simple alias, but for allowGeneric I don't think it's its responsibility.

[bradzacher]

thanks for this!