When doing a reflog walk, we use the commit's date to
do any date limiting. In earlier versions of Git, this could
lead to nonsense results, since a skipped commit would
truncate the traversal. So a sequence like:
git commit ...
git checkout week-old-branch
git checkout -
git log -g --since=1.day.ago
would stop at the week-old-branch, even though the "git
commit" entry further back is still interesting.
As of the prior commit, which uses a parent-less traversal
of the reflog, you get the whole reflog minus any commits
whose dates do not match the specified options. This is
arguably useful, as you could scan the reflogs for commits
that originated in a certain range.
But more likely a user doing a reflog walk wants to limit
based on the reflog entries themselves. You can simulate
--until with:
git log -g @{1.day.ago}
but there's no way to ask Git to traverse only back to a
certain date. E.g.:
# show me reflog entries from the past day
git log -g --since=1.day.ago
This patch teaches the revision machinery to prefer the
reflog entry dates to the commit dates when doing a reflog
walk. Technically this is a change in behavior that affects
plumbing, but the previous behavior was so buggy that it's
unlikely anyone was relying on it.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The reflog-walk system works by putting a ref's tip into the
pending queue, and then "traversing" the reflog by
pretending that the parent of each commit is the previous
reflog entry.
This causes a number of user-visible oddities, as documented
in t1414 (and the commit message which introduced it). We
can fix all of them in one go by replacing the fake-reflog
system with a much simpler one: just keeping a list of
reflogs to show, and walking through them entry by entry.
The implementation is fairly straight-forward, but there are
a few items to note:
1. We obviously must skip calling add_parents_to_list()
when we are traversing reflogs, since we do not want to
walk the original parents at all. As a result, we must call
try_to_simplify_commit() ourselves.
There are other parts of add_parents_to_list() we skip,
as well, but none of them should matter for a reflog
traversal:
- We do not allow UNINTERESTING commits, nor
symmetric ranges (and we bail when these are used
with "-g").
- Using --source makes no sense, since we aren't
traversing. The reflog selector shows the same
information with more detail.
- Using --first-parent is still sensible, since you
may want to see the first-parent diff for each
entry. But since we're not traversing, we don't
need to cull the parent list here.
2. Since we now just walk the reflog entries themselves,
rather than starting with the ref tip, we now look at
the "new" field of each entry rather than the "old"
(i.e., we are showing entries, not faking parents).
This removes all of the tricky logic around skipping
past root commits.
But note that we have no way to show an entry with the
null sha1 in its "new" field (because such a commit
obviously does not exist). Normally this would not
happen, since we delete reflogs along with refs, but
there is one special case. When we rename the currently
checked out branch, we write two reflog entries into
the HEAD log: one where the commit goes away, and
another where it comes back.
Prior to this commit, we show both entries with
identical reflog messages. After this commit, we show
only the "comes back" entry. See the update in t3200
which demonstrates this.
Arguably either is fine, as the whole double-entry
thing is a bit hacky in the first place. And until a
recent fix, we truncated the traversal in such a case
anyway, which was _definitely_ wrong.
3. We show individual reflogs in order, but choose which
reflog to show at each stage based on which has the
most recent timestamp. This interleaves the output
from multiple reflogs based on date order, which is
probably what you'd want with limiting like "-n 30".
Note that the implementation aims for simplicity. It
does a linear walk over the reflog queue for each
commit it pulls, which may perform badly if you
interleave an enormous number of reflogs. That seems
like an unlikely use case; if we did want to handle it,
we could probably keep a priority queue of reflogs,
ordered by the timestamp of their current tip entry.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When git-rev-list sees no pending commits, it shows a usage
message. This works even when reflog-walking is requested,
because the reflog-walk code currently puts the reflog tips
into the pending queue.
In preparation for refactoring the reflog-walk code, let's
explicitly check whether we have any reflogs to walk. For
now this is a noop, but the existing reflog tests will make
sure that it kicks in after the refactoring. Likewise, we'll
add a test that "rev-list -g" without specifying any reflogs
continues to fail (so that we know our check does not kick
in too aggressively).
Note that the implementation needs to go into its own
sub-function, as the walk code does not expose its innards
outside of reflog-walk.c.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Since its inception, the general strategy of the reflog-walk
code has been to start with the tip commit for the ref, and
as we traverse replace each commit's parent pointers with
fake parents pointing to the previous reflog entry.
This lets us traverse the reflog as if it were a real
history, but it has some user-visible oddities. Namely:
1. The fake parents are used for commit selection and
display. So for example, "--merges" or "--no-merges"
are not useful, because the history appears as a linear
string of commits. Likewise, pathspec limiting is based
on the diff between adjacent entries, not the changes
actually introduced by a commit.
These are often the same (e.g., because the entry was
just running "git commit" and the adjacent entry _is_
the true parent), but it may not be in several common
cases. For instance, using "git reset" to jump around
history, or "git checkout" to move HEAD.
2. We reverse-map each commit back to its reflog. So when
it comes time to show commit X, we say "a-ha, we added
X because it was at the tip of the 'foo' reflog, so
let's show the foo reflog". But this leads to nonsense
results when you ask to traverse multiple reflogs: if
two reflogs have the same tip commit, we only map back
to one of them. Instead, we should show both.
3. If the tip of the reflog and the ref tip disagree on
the current value, we show the ref tip but give no
indication of the value in the reflog. This situation
isn't supposed to happen (since any ref update should
touch the reflog). But if it does, given that the
requested operation is to show the reflog, it makes
sense to prefer that.
This commit adds a new script with several expect_failure
tests to demonstrate the problems. This could be part of
the existing t1411, but it's a bit easier to start from a
fresh state, where we know exactly what will be in the log.
Since the new multiple-reflog tests are checking the actual
output, we can drop the "make sure we don't segfault" tests
from t1411, which are a strict subset of what we're doing
here.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
