Support for "jsx": "preserve" config

After issue #58 I’ve realized that we have no support for this options in config which leads to errors that user can’t understand. Possible solutions:

1. Find a way to activate babel-jest transformer from jest config after ts-jest applied.
2. Inform user that this option is not allowed and use "jsx": "react" instead.
3. Include babel-jest transformer in our package and run it if "jsx": "preserve" is used.

As for me third solution seems to be the worst. First of all we have to create tests for this case.

[kelly-tock]

I can’t seem to get a react element test to work with ts-jest, and tsconfig: preserve. I reproduced the test using https://github.com/wmonk/create-react-app-typescript, so I know my test is ok.

TypeScript compiler encountered syntax errors while transpiling. Errors: '>' expected.,Unterminated regular expression literal.,',' expected.,')' expected.

I tried setting it to react in jsx, still same message.

my transforms:

    "^.+\\.(js|jsx)$": "<rootDir>/node_modules/babel-jest",
    "^.+\\.(ts|tsx)$": "ts-jest",

any ideas what that message means?

non react tests work like a charm thus far.

[jbrantly]

BTW, I think this issue is bigger than just JSX. There are a lot of other things that Babel can do beyond just JSX (for instance, the actual implementation side of “allowSyntheticDefaultImports”). I tend to use TypeScript for type-checking and Babel for transpilation for this reason.

Additionally, while I was able to easily chain TypeScript and Babel using a custom preprocessor, I can’t quite get code coverage working. So in the case of 1 or 3, some additional work might be needed to make sure code coverage still works. And if anyone has any tips on making that work manually that’d be awesome.