Add support for 'deep' extension

[dirkgroenen]

Typescript has support for deep config extensions, but it seems like tsconfig-paths isn't handling this too well and stops after the first 'extend'.

This rewrite makes sure it 'keeps on extending' until no 'extends' property is found.

[codecov]

Codecov Report

Merging #112 into master will not change coverage by %.
The diff coverage is n/a.

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[dirkgroenen]

Hi @jonaskello, any change of checking this out and getting it merged? :)

[effervescentia]

hey @jonaskello I'm running into the same problem trying to use a tool many steps removed from your own library (dependency-cruiser)

My company has a fairly complex typescript configuration setup which we have extracted to a config that is extended from multiple levels deep, as a result the paths configuration that is inherited is unfortunately ignored by your library.
Perhaps you could update your tsconfig resolution to just use what is provided out-of-the-box by typescript itself to avoid needing to concern yourself with the details of how config extension actually works

https://typestrong.org/ts-node/api/interfaces/TSCommon.html#readConfigFile
https://typestrong.org/ts-node/api/interfaces/TSCommon.html#parseJsonConfigFileContent

you should be able to use something like the following

import typescript from 'typescript';

const rawConfig = typescript.readConfigFile('tsconfig.json', typescript.sys.readFile);

const fullConfig = typescript.parseJsonConfigFileContent(
  rawConfig.config,
  typescript.sys,
  'path/to/repo',
  {},
  'tsconfig.json'
);

fullConfig.options; // tsconfig compiler options (with all inherited values)

ironically I originally saw this while exploring the codebase of dependency-cruiser trying to get to the bottom of this issue
https://github.com/sverweij/dependency-cruiser/blob/master/src/config-utl/extract-ts-config.js#L52

I'm also happy to make a PR with the above change if you like the solution but don't have the time to implement it