Re: [PATCH] t0021: make sure clean filter runs

[Junio C Hamano <gitster@pobox.com>]

Thomas Gummerer <t.gummerer@gmail.com> writes:

> It will also check the contents if the mtime is greater than the
> timestamp of the index, so the 'touch' here would also cover that.
>
> So the changes here do solve the race completely.

OK, the explanation makes sense.

Either test.r has been correctly checked out and has an older
timestamp or a more recent timestamp. In the former case, the index
knows that we did not touch it, so the next "checkout" knows it does
not have to ask the clean filter to work on it.  In the latter case,
the index is unsure if we touched it (or, suspects that it has
updated contents in it), so the clean filter needs to read from the
working tree to see if we did change it (and we find it is not
modified).  The outcome at the higher level, the answer to the
question "checkout" wanted to ask, is the same: test.r has no local
modificaiton and we can switch branches safely.

And that is already validated by seeing what exit status "checkout"
gives us, so it sort-of feels to be testing a bit too low level
implementation detail to see on which paths the filters are or are
not called, but that is not a problem with this fix.  If we want to
check at that level, we should do so correctly, and making sure that
the test.r file has recent timestamp to convince "checkout" that it
needs to verify contents is the right thing to do.

Thanks.