Re: [PATCH] add: don't write objects with --dry-run

Ævar Arnfjörð Bjarmason [off-list ref] writes:

I think the "git fetch --dry-run" command behaves like this too,
i.e. doesn't update refs, but fetches and writes objects.

For the patch I hacked up I think it's easy to argue that it shouldn't
do compression etc.

For this sort of thing and "fetch" I'm not so sure. Do we really know
that there aren't people who rely on this for say the performance of
seeing what an operation would do, and then not pay as much for the
"real one" that updates the index/refs/etc. later? Is that subsequent
"fetch" cheaper because of the --dry-run?

The answer to the last one is an easy "yes".  Trying to gauge the
time it would take for a real fetch with "--dry-run" is a losing
battle, I would think, as the pre-fetching would make the "real" one
cheaper, so from that point of view, I think we can ignore those who
time "--dry-run" and try to figure out anything meaningful.

This in any case is an interesting area, as the definition of
correctness of what "dry-run" does can be quite fuzzy.  As long as
it does not change the index, "git add --dry-run", even if it writes
objects or detects filesystem corruption by noticing I/O error while
compressing the data taken from the working tree files, is still
correct and the patch in question is not technically a bugfix (it is
a performance thing).  "git fetch --dry-run" would fall into the
same category, so would "git hash-object" without "-w".

All can use performance enhancement without breaking existing users,
I would think.

Thanks.