[pepoluan]

And how do you define "backwards compatible"?

How can you be sure that something is "backwards compatible"?

By running tests. And as it happens, the original coreutils did not have a test for this particular edge case.

Now that a divergence of behavior has been observed, all parties -- the coreutils devs and the uutils devs -- have agreed that this is an unacceptable regression and created new test cases to prevent the same misbehavior from happening again.

[pclmulqdq]

A lot of database companies go to great lengths to be bug-for-bug compatible with postures. This does happen. It takes some effort, though, which does not appear to have been applied in the case of this rewrite.

[secondcoming]

> And how do you define "backwards compatible"?

Backwards compatible means it's a drop-in replacement.

> How can you be sure that something is "backwards compatible"?

You compare the outputs from the same inputs.

> the original coreutils did not have a test for this particular edge case

So? 'man date' shows this argument option. Just because there was no existing unit test for it doesn't mean it's ok to break it. It would have taken literally 10 seconds to compare the outputs from the old and new program.