tsdx ignores tsconfig.json "extends" keyword

Current Behavior

There’s an extends feature in tsconfig which allows configuration inheritance across multiple tsconfig files. This however isn’t recognized in tsdx, which parses tsconfig here:

https://github.com/jaredpalmer/tsdx/blob/4f6de1083393057903a1837fb6658f8058ee832f/src/createRollupConfig.ts#L46-L49

The JSON object is used as-is, instead of drilling up to resolve parent config.

Expected behavior

tsdx should process extends just like tsc does.

Suggested solution(s)

In a quick look through TypeScript’s source code I couldn’t find the place where extends is handled, but it’s possible that TypeScript’s exported tsconfig parsing functions might handle extends for us automatically. See https://github.com/microsoft/TypeScript/blob/760393f893358a462b00eef7e8fb92342b0f71ad/lib/typescript.d.ts#L3639-L3647 what what TS offers in its API. The implementation is here: https://github.com/Microsoft/TypeScript/blob/6487d1ffe0d903b1e55a187ddeb973fe0d445a2f/src/compiler/parser.ts#L717

Additional context

This problem is similar to #483 in that both this issue and that one are caused by parsing tsconfig differently than tsc does.

Your environment

Software	Version(s)
TSDX	tsdx@0.12.3
TypeScript	typescript@3.7.5
Browser	n/a (this is a build issue)
npm/Yarn	yarn@1.21.1
Node	v12.13.1
Operating System	MacOS Catalina 10.15.2

[agilgur5]

ok. @agilgur5 we’re piling up quite a few PR’s for jared to review, lets slow down so that we dont swamp him with too much stuff.

@sw-yx think that might be the first time I’ve been asked to contribute less 🤔 🤔 🤔

[agilgur5]

anyone want to tackle this?

Oh, I already did hah. @justingrant said he didn’t have time for this in https://github.com/jaredpalmer/tsdx/issues/483#issuecomment-581238335 so I made the solution myself (see above reference). Still need to add a test for the extends case, hence the draft, but will do that in a day or few as I have to focus on some other things