Add option for "allow-namespace-imports" to noDuplicateImports rule

[EdwardDrapkin]

PR checklist

• Addresses an existing issue: no-duplicate-imports false positive with namespace imports #3418

Overview of change:

Adds an option "allow-namespace-imports" that can be passed to the no duplicate imports rule that will make it skip over lines containing namespace imports.

This option will fix the following fairly common pattern that currently errors the rule:

import * as React from 'react';
import { NamedExoticComponent } from 'react';

With the option set, the following error is still caught:

import * as React from 'react';
import { NamedExoticComponent } from 'react';
import { ExoticComponent } from 'react';

When the new option is enabled, wildcard imports will be allowed on a separate line from named imports, but the rule will still fail for multiple lines of named imports as well as multiple wildcard imports from the same module. To enable the new behavior pass the following object as an option to the rule in your tslint.json: { "allow-namespace-imports": true }

CHANGELOG.md entry:

[new-rule-option] added allow-namespace-imports option to no-duplicate-imports rule

[palantirtech]

Thanks for your interest in palantir/tslint, @EdwardDrapkin! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[JoshuaKGoldberg]

Mostly looks great! Nice clean change. 😄 Just some simplification internally and future-proofing of the options.

It looks like the lint build task is failing because of a couple of Prettier complaints; you'll want to fix those up too.

[EdwardDrapkin]

Thanks for the feedback.

I believe I have addressed all your issues, but for brevity, here are my comments on your comments.

1. I updated the call to pass options to ctx per your suggestion. Didn't know this was possible, thanks for the help.

2. I figured out how to write tests and added a test case for this option because the option is a bit more complex. I believe I covered all of the possible permutations of error/not error when the rule is enabled.

3. I updated the rule options to be an object with the format { "allow-namespace-imports": boolean }.

4. The rule now tracks named imports separately from namespace imports. The benefit is that now multiple wildcard imports will error out alongside multiple named imports. You also get a separate, special error message specifically for multiple wildcard imports.

5. I updated the changelog entry suggestion, but I fear I may have taken it from too short to too long.

Thanks for your help!!

[EdwardDrapkin]

Looks like all the tests passed this time 🎉

[JoshuaKGoldberg]

Fantastic, thanks @EdwardDrapkin! 💖

[JoshuaKGoldberg]

Yes, the changelog entry is a bit too long haha. I'll go ahead and edit it.

[huyz]

Is there a reason why this option isn't the default?

[JoshuaKGoldberg]

@huyz it happened not to be in this PR, but that's a good idea. Perhaps it should - would you mind filing a new issue?

[EdwardDrapkin]

Is there a reason why this option isn't the default?

I didn't want to presume to change default behavior is the only reasoning I had to make it opt-in instead of opt-out.

[naingaungphyo]

Is there any reason or advantages for not using React.NamedExoticComponent and React.ExoticComponent, like we use React.Component only with one import statement(1st line).