Add allowTsInNodeModules option for importing .ts files from node_modules.

[aelawson]

Summary:

This PR adds an allowTsInNodeModules option that will allow importing of .ts modules from a node_modules subdirectory / dependency. At the time of writing, this will function as a "whitelist" - the user must manually add the desired files(s) or module(s) to the files or include block of their tsconfig.json, respectively. Otherwise, they will receive an error that nothing has been emitted as before with additional text suggesting this option if they really need it.

Changes:

• Added allowTsInNodeModules option.
• Updated error message when a module is imported from node_modules without this option enabled.
• Updated the nodeModulesMeaningfulErrorWhenImportingTs test outputs and have added a new allowTsInNodeModules test (with the option enabled) for TS 2.8.
• Updated README to include this option.

As most recently discussed here:
#278

And also here:
#365
microsoft/TypeScript#12358

[johnnyreilly]

Thanks for the thorough PR @aelawson! I'm getting failing tests on the build servers. It occurs to me that an execution test would likely work just as well here. Given that the comparison tests can be a world of pain, do you fancy trying putting together an execution test instead? I think that you can probably clone this one:

https://github.com/TypeStrong/ts-loader/tree/master/test/execution-tests/nodeResolution

And quickly tweak it into an execution test. Want to give it a whirl?

[aelawson]

@johnnyreilly Sure I'll change the test to be an execution test :) Yeah, looks like one of the failures was me forgetting to update the test output after a small change, d'oh.

[aelawson]

@johnnyreilly I have updated the test to be an execution test - looks like builds are passing now. Let me know if you've got any other concerns!

[johnnyreilly]

Nice - thanks for the hard work! I'll set aside some time to review it very soon!

[johnnyreilly]

Can we linkify this please? i.e. [https://github.com/Microsoft/TypeScript/issues/12358](https://github.com/Microsoft/TypeScript/issues/12358) I think

[johnnyreilly]

Can we turn this into a ternary please? Something like:

const additionalGuidance = (!options.allowTsInNodeModules && filePath.indexOf('node_modules') !== -1)
    ? " By default, ts-loader will not compile .ts files in node_modules.\n" +
      "You should not need to recompile .ts files there, but if you really want to, use the allowTsInNodeModules option.\n" +
      "See: https://github.com/Microsoft/TypeScript/issues/12358"
    : "";

[johnnyreilly]

Also, can we lose the comparison test now we have an execution test please?

[aelawson]

@johnnyreilly Done. Just to double check on one thing: the remaining comparison test is the existing nodeModulesMeaningfulErrorWhenImportingTs test that checks for a meaningful error if a user hasn't enabled this option - you're okay with getting rid of that?

[johnnyreilly]

Hey @aelawson,

I want to keep nodeModulesMeaningfulErrorWhenImportingTs please; that's still useful. Just wanted to get rid of the new comparison test since you've been able to come up with an execution test instead. I prefer execution tests but they're not always appropriate.

[aelawson]

@johnnyreilly That comparison test has been deleted :P The only changes to comparison tests left in the PR are for the nodeModulesMeaningfulErrorWhenImportingTs and validateLoaderOptions tests :)

[johnnyreilly]

Nice one! I'm not near a computer for the next half week or so. Once I am I'll look to merge and arrange a release. Thanks for your work!

[aelawson]

Cool sounds good :)