feat(eslint-plugin): add extension rule no-duplicate-imports

[yeonjuan]

fixes #2315

I made an extension rule which distinguishes type-only import from standard import. :)

[typescript-eslint]

Thanks for the PR, @yeonjuan!

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!

---

🙏 Please, if you or your company is finding typescript-eslint valuable, help us sustain the project by sponsoring it transparently on https://opencollective.com/typescript-eslint. As a thank you, your profile/company logo will be added to our main README which receives thousands of unique visitors per day.

[codecov]

Codecov Report

Merging #2609 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2609      +/-   ##
==========================================
+ Coverage   92.82%   92.84%   +0.01%     
==========================================
  Files         293      294       +1     
  Lines        9619     9657      +38     
  Branches     2697     2709      +12     
==========================================
+ Hits         8929     8966      +37     
  Misses        326      326              
- Partials      364      365       +1     

Flag	Coverage Δ
#unittest	92.84% <ø> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
packages/eslint-plugin/src/configs/all.ts	100.00% <ø> (ø)
...es/eslint-plugin/src/rules/no-duplicate-imports.ts	97.36% <ø> (ø)

[bradzacher]

LGTM - thanks for your contribution!

[bradzacher]

Wait... is this really how the base rule works?

What is wrong with the code

import { T } from 'foo';
export { A } from 'foo';

This seems like it's much better than

import { T, A } from 'foo';
export { A };

Because the latter code defines a local variable for no reason.

[yeonjuan]

@bradzacher right! This rule seems just focus on duplicate module sources.🤣

[richard-viney]

I've run into some false positives with this rule when used with import type.

Specifically, the following code triggers this new rule:

import type Foo from "my-module"
import type { Bar } from "my-module"

But it is not actually possible to write

import type Foo, { Bar } from "my-module"

because that results in the TypeScript error

A type-only import can specify a default import or named bindings, but not both.ts(1363)

This rule may need some additional logic to handle this case.

[bradzacher]

please file a new issue.

[richard-viney]

New issue is here: #2636

[ginger-kang]

Hi :)
Isn't this rule id should be no-duplicate-imports, not no-dupe-class-members?