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!

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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 #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?