Rule proposal: no-duplicate-named

[jfmengels]

I just noticed the the following is considered to be valid syntax by both espree and babel-eslint.

import {a, a, b as a, c as a} from 'foo';

We should add a rule that forbids:

• Importing a named export twice: {a, a}
• Importing a named export and naming it after another imported named export: {a, b as a}
• Importing a named export and naming it after the name of another renamed imported named export: {b as a, c as a}

To discuss:

• Importing a named export and naming it the original name of an other renamed imported named export: {b as a, c as b}

I'm pretty sure we had a rule to forbid import {b as a} from 'foo' when a is also a named export of that module, but I don't remember which one. If we don't, let me know, and I'll create an issue, because that sounds like a nice style issue to have. That might fill the role of the last to discuss item?

I propose the name no-duplicate-named, but I'm open to better names :)

[ntdb]

I might take a crack at this.

no-named-as-default seems to be the closest existing rule to the one you're describing. It prevents the use of a named export's name when importing the default export. Docs. Perhaps that rule could be generalized for the case you're describing?

[jfmengels]

That'd be great @ntdb! Just wait on a :+1: from @benmosher maybe?

Yes, no-named-as-default is very close. I think we can copy most of the logic inside it, but it should be a separate rule, as it would be an unwarranted breaking change IMO (an the name would be misleading).

[ljharb]

@ntdb any chance you'd be able to still make this PR?