Fossil

files in faultless finished form. A wish for collapsed, finalized
check-ins is a wish for a counterfactual situation.

The common counterargument is that collapsed check-ins represent a
better world, the ideal we’re striving for. What that argument overlooks
is that we must throw away valuable information to get there.

### <a name="empathy"></a>7.1 Individual check-ins support developer empathy

Ideally, future developers of our software can understand every feature
in it using only context available in the version of the code they start
work with. Prior to widespread version control, developers had no choice
but to work that way.  Pre-existing codebases could only be understood
as-is or not at all.  Developers in that world had an incentive to
develop software that was easy to understand retrospectively, even if

check-in it was a part of — and then to understand the surrounding
check-ins as necessary — than it is to understand a 500-line check-in
that collapses a whole branch’s worth of changes down to a single
finished feature.

[sdm]: ./fossil-v-git.wiki#durable

### <a name="bisecting"></a>7.2 Bisecting works better on small check-ins

Git lets a developer write a feature in ten check-ins but collapse it
down to an eleventh check-in and then deliberately push only that final
collapsed check-in to the parent repo. Someone else may then do a bisect
that blames the merged check-in as the source of the problem they’re
chasing down; they then have to manually work out which of the 10 steps
the original developer took to create it to find the source of the
actual problem.

Fossil pushes all 11 check-ins to the parent repository by default, so
that someone doing that bisect sees the complete check-in history, so
the bisect will point them at the single original check-in that caused
the problem.

### <a name="comments"></a>7.3 Multiple check-ins require multiple check-in comments

The more comments you have from a given developer on a given body of
code, the more concise documentation you have of that developer’s
thought process. To resume the bisecting example, a developer trying to
work out what the original developer was thinking with a given change
will have more success given a check-in comment that explains what the
one check-in out of ten blamed by the “bisect” command was trying to
accomplish than if they must work that out from the eleventh check-in’s
comment, which only explains the “clean” version of the collapsed
feature.

### <a name="cherrypicking"></a>7.4 Cherry-picks work better with small check-ins

While working on a new feature in one branch, you may come across a bug
in the pre-existing code that you need to fix in order for work on that
feature to proceed. You could choose to switch briefly back to the
parent branch, develop the fix there, check it in, then merge the parent
back up to the feature branch in order to continue work, but that’s
distracting. If the fix isn’t for a critical bug, fixing it on the

complete. If a support organization must manually disentangle a fix from
a feature check-in, they are likely to introduce new bugs on the stable
branch. Even if they manage to do their work without error, it takes
them more time to do the cherry-pick that way.

[rh]: https://en.wikipedia.org/wiki/Red_Hat

### <a name="backouts"></a>7.5 Back-outs also work better with small check-ins

The inverse of the cherry-pick merge is the back-out merge. If you push
only a collapsed version of a private working branch up to the parent
repo, those working from that parent repo cannot automatically back out
any of the individual check-ins that went into that private branch.
Others must either manually disentangle the problematic part of your
merge check-in or back out the entire feature.