(feat) Support tsconfig extends

[dummdidumm]

Fixes #300

I was unsure about the boolean/string behavior of the options, especially because it is mentioned nowhere in the docs that boolean is a valid option.

Also, if I understand this correctly, by default the tsconfig.json is not picked up if I do sveltePreprocess()?

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Tests

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[kaisermann]

Thanks for this! Will give it a look later

Also, if I understand this correctly, by default the tsconfig.json is not picked up if I do sveltePreprocess()?

It is! If tsconfigFile is not false (the boolean that is not documented 😳 ), we start looking for the tsconfig.json in the dirname(filename).

https://github.com/sveltejs/svelte-preprocess/blob/main/src/transformers/typescript.ts#L69

[dummdidumm]

converting to absolute path here because else parseJsonConfigFileContent doesn't seem to work

[kaisermann]

🎉 neat 🎉 . Released in 4.7.0