🐛 noUnusedImports does not detect used types

[EvHaus]

Environment information

Incompatible Biome Server: ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

ℹ Rage discovered this running server using an incompatible version of Biome.

Server:
  Version:                      1.2.2

What happened?

When the nursery/noUnusedImports rule is used in a file where a type is imported, it will detect that import as unused (even though it's actually used).

import type NextAuth from 'next-auth/next';
const a: typeof NextAuth = {}

Expected result

Because the import is actually used, it should not be flagged for removal.

Code of Conduct

• I agree to follow Biome's Code of Conduct

[Conaclos]

This is intentional. typeof can only be applied on a value, not a type. Are you sure that your code is correct? How is defined NextAuth?

[netner-d]

@Conaclos typeof can be applied to a variable imported as a type

[netner-d]

I have the same issue on my side

import type * as Config from './objects/config'; // -> Config is reported as unused
type ConfigCheck<T extends CheckObject<Omit<typeof Config, never>> = Omit<typeof Config, never>> =
  T;

[Conaclos]

In my view, Config should be imported as a value:

import * as Config from './objects/config'; // -> Config is reported as unused
type ConfigCheck<T extends CheckObject<Omit<typeof Config, never>> = Omit<typeof Config, never>> =
  T;

Taking some time to investigate, it seems that TypeScript allows the use of a type in typeof in only one case: if the type is imported. This could avoid conflicts with verbatimModuleSyntax mode. I have to investigate more to be sure about that.

[EvHaus]

Maybe we need a rule for detecting when you're unnecessarily using typeof on an imported type :)

Although, TypeScript yells at me if I try to remove it:

import type NextAuth from 'next-auth/next';

// 'NextAuth' refers to a value, but is being used as a type here. Did you mean 'typeof NextAuth'?
const a: NextAuth = {}

This works though:

import NextAuth from 'next-auth/next';
const a: typeof NextAuth = {}

[Conaclos]

Yes this conflicts with verbatimModuleSyntax.
I shipped a fix on main which allows using imported type in a typeof.
You can test on the playground that the fix solves your issue :)