feat: add option to run TypeScript diagnostics

[alan-agius4]

By creating a program we are enabled to run diagnostics on typescipt files in order to emit semantic errors. For the time being I only used one of the many methods this one is getPreEmitDiagnostics

This enables syntactic & semantic TypeScript error reporting

[kulshekhar]

@alan-agius4 Thanks for taking the time to create the PR :)

I just have one question - is ts-jest the right place for this? It sounds like something that should be done via an npm script using tsc.

Also, should this discussion result in merging, all tests (currently failing) will need to pass.

[alan-agius4]

Test have been fixed.

Well, as a matter of fact I actually did expect this was provided by ts-jest and on by default and maybe a lot of people think the same, they just never realized it doesn't, and I have used ts-jest for some time now, but only recently noticed that this is not supported.

I used Karma before and still do now. and for Karma users this is something that comes out side of the box if you use the typescript plugin. Having it as an npm script it's a possibility but like that you'll lose the benefits of jest caching and also having to run a npm script to valid your code prior to using ts-jest for me makes ts-jest a bit redundant as than I can use the transpiled JS to run the tests on. For me it doesn't make that much sense to transpile twice especially considering I have a lot of code.

[kulshekhar]

I've actually resisted this feature for long but it seems more and more people want it. So I'm okay with this PR.

@alan-agius4 Could you also:

• bump the version patch in package.json so that this can be published right away
• update the AUTHORS file with your name/email in alphabetical order?

[alan-agius4]

Bumped and added myself to the authers

[alan-agius4]

One quick thing, shouldn't the bump be a minor instead of a patch since it's a feature? or you are not following semver?

[kulshekhar]

yeah - we don't follow semver. We follow Jest's major version but beyond that it's a bit arbitrary.

[kulshekhar]

Merged and published.

Thanks again for the PR @alan-agius4 😃

[alan-agius4]

glad to help 😄