feat: support type imports

[SimenB]

Very rough start on #3695. Not sure how you want to handle this. I'll probably just do the ones we need at work (which means Apollo TS), but it should be fine to expand as we go?

(is there some watch mode I can run that builds as we go? right now I do a full yarn build every time I change something, which seems suboptimal)

[SimenB]

Only reason for an option rather than being default behavior is that it requires TS 3.8. Maybe some "minimum TS version" rather than an explicit option makes more sense?

[dotansimha]

This is awesome! Thank you @SimenB !

This could work, and could be optional via configuration. What about importing enums and other things? how is it effected? because mappers can import not only TS types

[SimenB]

Are enums imported as values anywhere? The test should probably try to compile the module we generate with isolatedModules: true and importsNotUsedAsValues: error. I don't think I know enough about your setup to add that, though

https://github.com/Microsoft/TypeScript/wiki/Using-the-Compiler-API#a-simple-transform-function

[ardatan]

For example, there are const enums used as values not types. So I think import type would break this behavior.

[SimenB]

const enum aren't supported by isolatedModules regardless, so I wouldn't want them 😃

[vatosarmat]

Any chances this useful feature to be merged? 😺
Since it is optional and disabled by default, it shouldn't break anything for anyone.

[dotansimha]

@vatosarmat merging :)
I'm merging it now, and will push some fixes soon to make sure all codebase supports that.

Thanks @SimenB , sorry it took so long.

[theguild-bot]

The latest changes of this PR are available as alpha in npm: 1.17.5-alpha-f389301a.0

Quickly update your package.json by running:

npx match-version @graphql-codegen 1.17.5-alpha-f389301a.0

[SimenB]

Thanks @dotansimha! I believe this was still incomplete, happy to hear you'll fix the missing parts 👍

I wanted to add some tests with isolatedModules: true and importsNotUsedAsValues: error, but didn't get around to it. I believe such tests would be quite useful to ensure no regressions. Never got around to it, though 😅

[SimenB]

Tested this out now in the new release, and it works for some cases. However, it does not affect

• from 'graphql': feat(typescript-resolvers): use import type when importing from graphql #4437
• from '@apollo/react-common' feat(react-apollo): generate type imports #4448
• imports from near-operation-file's baseTypesPath feat: support type imports in near-operation-file preset #4436
• fragment imports (possibly from near-operation-file?) feat: support type imports in near-operation-file preset #4436

@dotansimha My OSS backlog is really long right now, so I won't be able to work on this to properly polish it. 🤞 you can 😀