feat: Move shared types into their own package

[bradzacher]

Fixes #330, #335, #413

Happy to change the name of the package, wasn't sure what to call it.

This PR moves the ESLint override types (and the createRule function) out of the eslint-plugin package and into a new package.

This should make it easier for people to consume our libraries when writing rules they don't want to submit here (because they're internal rules, etc), or when they're writing an eslint plugin in typescript.

[codecov]

Codecov Report

Merging #425 into master will decrease coverage by 0.73%.
The diff coverage is 68.88%.

@@            Coverage Diff            @@
##           master    #425      +/-   ##
=========================================
- Coverage   96.23%   95.5%   -0.74%     
=========================================
  Files          83      88       +5     
  Lines        4067    4093      +26     
  Branches     1149    1150       +1     
=========================================
- Hits         3914    3909       -5     
- Misses         52      82      +30     
- Partials      101     102       +1

Impacted Files	Coverage Δ
...ackages/eslint-plugin/src/rules/prefer-includes.ts	100% <ø> (ø)	⬆️
...slint-plugin/src/rules/no-unnecessary-qualifier.ts	96.07% <ø> (ø)	⬆️
packages/eslint-plugin/src/rules/array-type.ts	91.35% <ø> (ø)	⬆️
packages/eslint-plugin/src/rules/member-naming.ts	100% <ø> (ø)	⬆️
...plugin/src/rules/prefer-string-starts-ends-with.ts	100% <ø> (ø)	⬆️
...s/experimental-utils/src/eslint-utils/deepMerge.ts	88.23% <ø> (ø)
packages/typescript-estree/src/ast-converter.ts	100% <ø> (ø)	⬆️
packages/parser/src/scope/scopes.ts	100% <ø> (ø)	⬆️
...xperimental-utils/src/eslint-utils/applyDefault.ts	83.33% <ø> (ø)
...slint-plugin/src/rules/prefer-namespace-keyword.ts	100% <ø> (ø)	⬆️
... and 68 more

[JamesHenry]

This looks really good! I will start using it right away on the stuff I mentioned on slack.

However, please could we call it:

@typescript-eslint/experimental-utils

I think it would be really useful for it to initially not fall under proper semver to give us chance to "move fast and break things" for a bit. As we use it outside the monorepo we might well find things we need to tweak.

So we could have experimental in the name and then a corresponding disclaimer in the README of the package that that is what our plan is. "Feel free to use it, but no guarantees between minor version s"

We can then promote it to be just:

@typescript-eslint/utils

In v2.0.0.

WDYT?

[bradzacher]

@typescript-eslint/experimental-utils

Sounds like a good idea!
I'll make the change now :)

[SimenB]

Hello! 👋

This should make it easier for people to consume our libraries when writing rules they don't want to submit here (because they're internal rules, etc), or when they're writing an eslint plugin in typescript.

I tried to do this, and it broke horribly since the utils depend on typescript. Is that on purpose? I'd like to author the plugin in TS, but that shouldn't be visible to consumers of the plugin.

Sorta related, I got a type error in the test unless I specified the TS parser - are the plugins compatible with the standard parser, or will the type safety be wrong if another parser is used?

Ref jest-community/eslint-plugin-jest#269

[bradzacher]

@SimenB - there's no direct dependency on typescript, but there is a peer dependency:
https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/experimental-utils/package.json#L42-L45

The package re-exports some things from typescript-estree via the default entry point
https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/experimental-utils/src/index.ts#L9-L14

Which causes the package to init, and it has a dependency of typescript (it's marked as a peer dep to help out the create-react-app folks that do some dual install stuff (#443).

I'll put up a fix so that this doesn't happen.

[SimenB]

Ah, that's awesome! Thanks.

Thoughts on not specifying parser in RuleTester?

typescript-eslint/packages/experimental-utils/src/ts-eslint/RuleTester.ts

Line 58 in fac5c7d

parser: '@typescript-eslint/parser';

I'd like to run tests with the default eslint parser

[bradzacher]

feel free to open a PR if you want!
I thought about that but was deferring on it till someone complained :)
Happy to have it as a generic so that it is easy to enforce a specific parser string at compile time.

[SimenB]

Hehe, fair enough! I'll see what I can do

Happy to have it as a generic so that it is easy to enforce a specific parser string at compile time.

How so? I thought to just make it parser?: string