rebase backends currently behave differently with empty commit messages,
largely as a side-effect of the different underlying commands on which
they are based. am-based rebases apply commits with an empty commit
message without stopping or requiring the user to specify an extra flag.
(It is interesting to note that am-based rebases are the default rebase
type, and no one has ever requested a --no-allow-empty-message flag to
change this behavior.) merge-based and interactive-based rebases (which
are ultimately based on git-commit), will currently halt on any such
commits and require the user to manually specify what to do with the
commit and continue.
One possible rationale for the difference in behavior is that the purpose
of an "am" based rebase is solely to transplant an existing history, while
an "interactive" rebase is one whose purpose is to polish a series before
making it publishable. Thus, stopping and asking for confirmation for a
possible problem is more appropriate in the latter case. However, there
are two problems with this rationale:
1) merge-based rebases are also non-interactive and there are multiple
types of rebases that use the interactive machinery but are not
explicitly interactive (e.g. when either --rebase-merges or
--keep-empty are specified without --interactive). These rebases are
also used solely to transplant an existing history, and thus also
should default to --allow-empty-message.
2) this rationale only says that the user is more accepting of stopping
in the case of an explicitly interactive rebase, not that stopping
for this particular reason actually makes sense. Exploring whether
it makes sense, requires backing up and analyzing the underlying
commands...
If git-commit did not error out on empty commits by default, accidental
creation of commits with empty messages would be a very common occurrence
(this check has caught me many times). Further, nearly all such empty
commit messages would be considered an accidental error (as evidenced by a
huge amount of documentation across version control systems and in various
blog posts explaining how important commit messages are). A simple check
for what would otherwise be a common error thus made a lot of sense, and
git-commit gained an --allow-empty-message flag for special case
overrides. This has made commits with empty messages very rare.
There are two sources for commits with empty messages for rebase (and
cherry-pick): (a) commits created in git where the user previously
specified --allow-empty-message to git-commit, and (b) commits imported
into git from other version control systems. In case (a), the user has
already explicitly specified that there is something special about this
commit that makes them not want to specify a commit message; forcing them
to re-specify with every cherry-pick or rebase seems more likely to be
infuriating than helpful. In case (b), the commit is highly unlikely to
have been authored by the person who has imported the history and is doing
the rebase or cherry-pick, and thus the user is unlikely to be the
appropriate person to write a commit message for it. Stopping and
expecting the user to modify the commit before proceeding thus seems
counter-productive.
Further, note that while empty commit messages was a common error case for
git-commit to deal with, it is a rare case for rebase (or cherry-pick).
The fact that it is rare raises the question of why it would be worth
checking and stopping on this particular condition and not others. For
example, why doesn't an interactive rebase automatically stop if the
commit message's first line is 2000 columns long, or is missing a blank
line after the first line, or has every line indented with five spaces, or
any number of other myriad problems?
Finally, note that if a user doing an interactive rebase does have the
necessary knowledge to add a message for any such commit and wants to do
so, it is rather simple for them to change the appropriate line from
'pick' to 'reword'. The fact that the subject is empty in the todo list
that the user edits should even serve as a way to notify them.
As far as I can tell, the fact that merge-based and interactive-based
rebases stop on commits with empty commit messages is solely a by-product
of having been based on git-commit. It went without notice for a long
time precisely because such cases are rare. The rareness of this
situation made it difficult to reason about, so when folks did eventually
notice this behavior, they assumed it was there for a good reason and just
added an --allow-empty-message flag. In my opinion, stopping on such
messages not desirable in any of these cases, even the (explicitly)
interactive case.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This option allows commits with empty commit messages to be rebased,
matching the same option in git-commit and git-cherry-pick. While empty
log messages are frowned upon, sometimes one finds them in older
repositories (e.g. translated from another VCS [0]), or have other
reasons for desiring them. The option is available in git-commit and
git-cherry-pick, so it is natural to make other git tools play nicely
with them. Adding this as an option allows the default to be "give the
user a chance to fix", while not interrupting the user's workflow
otherwise [1].
[0]: https://stackoverflow.com/q/8542304
[1]: https://public-inbox.org/git/7vd33afqjh.fsf@alter.siamese.dyndns.org/
To implement this, add a new --allow-empty-message flag. Then propagate
it to all calls of 'git commit', 'git cherry-pick', and 'git rebase--helper'
within the rebase scripts.
Signed-off-by: Genki Sky <sky@genki.is>
Reviewed-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
These are tests which are missing a link in their &&-chain,
but during a setup phase. We may fail to notice failure in
commands that build the test environment, but these are
typically not expected to fail at all (but it's still good
to double-check that our test environment is what we
expect).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Rebasing a commit that contains a diff in the commit message results
in a failure with output such as
First, rewinding head to replay your work on top of it...
Applying: My cool patch.
fatal: sha1 information is lacking or useless
(app/controllers/settings_controller.rb).
Repository lacks necessary blobs to fall back on 3-way merge.
Cannot fall back to three-way merge.
Patch failed at 0001 My cool patch.
The reason is that 'git rebase' without -p/-i/-m internally calls 'git
format-patch' and pipes the output to 'git am --rebasing', which has
no way of knowing what is a real patch and what is a commit message
that contains a patch.
Make 'git am' while in --rebasing mode get the patch body from the
commit object instead of extracting it from the mailbox.
Patch by Junio, test case and commit log message by Martin.
Reported-by: anikey <arty.anikey@gmail.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Martin von Zweigbergk <martin.von.zweigbergk@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Many scripts compare actual and expected output using
"diff -u". This is nicer than "cmp" because the output shows
how the two differ. However, not all versions of diff
understand -u, leading to unnecessary test failure.
This adds a test_cmp function to the test scripts and
switches all "diff -u" invocations to use it. The function
uses the contents of "$GIT_TEST_CMP" to compare its
arguments; the default is "diff -u".
On systems with a less-capable diff, you can do:
GIT_TEST_CMP=cmp make test
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This makes rebase/am keep the original commit log message
better, even when it does not conform to "single line paragraph
to say what it does, then explain and defend why it is a good
change in later paragraphs" convention.
This change is a two-edged sword. While the earlier behaviour
would make such commit log messages more friendly to readers who
expect to get the birds-eye view with oneline summary formats,
users who primarily use git as a way to interact with foreign
SCM systems would not care much about the convenience of oneline
git log tools, but care more about preserving their own
convention. This changes their commits less useful to readers
who read them with git tools while keeping them more consistent
with the foreign SCM systems they interact with.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
