Add ability to filter config options to files created after date - #2689

Codecov Report

❌ Patch coverage is 80.50847% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.44%. Comparing base (28330d9) to head (a266e65).

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##           develop    #2689      +/-   ##
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- Coverage    95.51%   95.44%   -0.07%     
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  Files          182      182              
  Lines        27830    27930     +100     
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+ Hits         26582    26658      +76     
- Misses        1248     1272      +24     

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@calda is the idea of this feature to avoid formatting existing files? If so I had a slightly different idea in mind:

I was thinking of adding a --snapshot feature that would capture the current state of the project, using the same hashing mechanism already employed by the cache.

the snapshot file would be saved in the project as something like .swiftformat-snapshot. Any files that match the hashes in the snapshot would be ignored for future formatting passes.

I think the snapshot idea is reasonable, but I think checking in a snapshot file is more complicated and visible than using the created-on date (for example, if a file is renamed, the snapshot file has to be updated).

We also would need the ability to only ignore existing violations for specific rules, rather than just ignoring all existing violations in a file.

I think both approaches are pretty reasonable with different situation where one makes more sense than the other.

No reason not to have both I suppose, but the neat feature of a snapshot is that files that are touched get opted back into formatting, whereas with the creation date they don't.

Unless you plan to support modified date as an alternative option?

In our case we specifically only want to apply the preferSwiftTesting rule to newly-created Swift files, and not apply it to existing Swift files. We want it to be alright to continue modifying existing XCTest files without them being auto-formatted to Swift Testing.