Feature: Allow a virtual file system

[JoshuaKGoldberg]

Hi! I've been using replace-in-file for a while now and really liking it. It's straightforward to use & works well. Thanks! ❤️

One pain point I have, though, is testing out code that calls to replace-in-file. There's no way (that I can find) right now to have replaceInFile() send its results to a callback rather than writing on disk. But some of its logic around capturing froms and passing them to to would be nontrivial to reimplement during tests. https://github.com/JoshuaKGoldberg/create-typescript-app/pull/1078/commits/67a31169ce652825989e4f2dcbe7cfa5a0334eb7 is an example of me extracting some code to somewhat test it.

Proposal: can replaceInFile be given a fs parameter that defaults to Node's fs?

const fileSystem = {
  readFile: vi.fn(),
  writeFile: vi.fn(),
};

replace({
  fileSystem,
  from: '...',
  to: '...',
});

Per https://github.com/search?q=repo%3Aadamreisnz%2Freplace-in-file+fs.+-path%3A*.spec*&type=code those four APIs look like the only ones being used in the async version. For .sync:

const fileSystemSync = {
  readFileSync: vi.fn(),
  writeFileSync: vi.fn(),
};

replace({
  fileSystem,
  from: '...',
  to: '...',
});

I'd be happy to send a PR if you'd accept it!

[adamreisnz]

Hey, that sounds like an interesting solution. So the fileSystem would default to Nodes functions, but would allow you to specify alternatives as well.

Yeah I'd be happy to accept a PR that allows that. I think it should even be fully backwards compatible.

[JoshuaKGoldberg]

Fixed by #177. Thanks!