Feature request: Consider TS imports with all type the same as type-only.

[alvaro-cuesta]

Context

TypeScript 4.5 added inline type imports. dependency-cruiser has support for 'type-only' in dependencyTypesNot, but this only works when using separate type imports, and not when all inline imports are qualified as type.

This can be fixed by moving the individual type imports to a separate type import, but this is cumbersome for some of us since using ESLint's consistent-type-imports with fixStyle: 'inline-type-imports' will prefer adding type inline even when all imports are type.

Some of us prefer this syntax since it makes it easier to mix type and non-type imports.

Expected Behavior

This rule:

{
  name: 'not-to-dev-dep',
  severity: 'error',
  comment:
    "This module depends on an npm package from the 'devDependencies' section of your " +
    'package.json. It looks like something that ships to production, though. To prevent problems ' +
    "with npm packages that aren't there on production declare it (only!) in the 'dependencies'" +
    'section of your package.json. If this module is development only - add it to the ' +
    'from.pathNot re of the not-to-dev-dep rule in the dependency-cruiser configuration',
  from: {
    path: '^(app)',
    pathNot: [
      '.(spec|test).(js|mjs|cjs|ts|ls|coffee|litcoffee|coffee.md)$',
      // allow dev depencendies in modules/testing as those are helpers for tests
      'modules/testing',
    ],
  },
  to: {
    dependencyTypes: ['npm-dev'],
    dependencyTypesNot: ['type-only'],
  },
},

(Note the dependencyTypesNot: ['type-only'] line which is new, different from default config.)

Should not be fired when using imports like this:

import { type SomeType, type OtherType } from 'my-dev-dependency';

Current Behavior

Correctly ignores devDependencies imports when using this syntax:

import type { SomeType, OtherType } from 'my-dev-dependency';

But this syntax trips the rule:

import { type SomeType, type OtherType } from 'my-dev-dependency';

Possible Solution

All members inside the import statement are qualified as type so it could be considered as 'type-only' for rule matching purposes.

Additionally I propose adding dependencyTypesNot: ['type-only'] to the default generated not-to-dev-dep rule. Importing types from dev dependencies is safe since they are erased at TS compile time. This would be a good way to ensure you're only importing types from dev dependencies.

Considered alternatives

1. Possibly leave it as is and just force using import type { ... } explicitly.
   • See "Context" section above on why it is inconvenient.
2. Introduce a new dependency type ('all-types'?)
   • Seems like it doesn't add much value and complicates things further.

[alvaro-cuesta]

I'd be willing to work on this if the suggested change is deemed appropriate.

[sverweij]

hi @alvaro-cuesta yep - good one to add! I missed that one when adding type only imports 😬.

Agree with slotting them in with the imports detected as type-only - and a pull request to add them is welcome.

The addition to the not-to-dev-dep rule in the default rule set is a good one as well. It should've been part of it when type only imports were introduced in dependency-cruiser. I've added it in #874.

[sverweij]

Hi @alvaro-cuesta as you can see the PR is merged - thanks again!

As it's a breaking change I'd like to combine its release with the other still open PR, so it's not part of today's release. Realising it might be useful nonetheless (and folks might want to try it out & provide feedback) I released both your PR and the other one with the beta tag as [email protected] on npmjs.

[alvaro-cuesta]

@sverweij my pleasure. Thanks for also releasing the beta version, I just bumped it in my project ❤️