git-rebase has lots of options that are mutually incompatible. Even among
aspects of its behavior that is common to all rebase types, it has a number
of inconsistencies. This series tries to document, fix, and/or warn users
about many of these.
Changes since v3 (range-diff included at the end):
* Fix many small issues mentioned by Junio and SZEDER, including a fix
suggested by Eric.
* Add a new patch (#6) which introduces technical documentation on directory
rename detection, so that...
* The more technical portion of the docs from patch 7 (used to be patch 5
in v3) can be moved from git-rebase.txt to the new
technical/directory-rename-detection.txt, as suggested by Junio.
* Also adds a new patch (#8) which adds testcases to demonstrate what the
new technical doc discusses.
Items of particular note for reviewers:
* I have left patch 9 (used to be patch 7) in RFC state, but
expanded the commit message with an in-depth usability rationale
for the change.
* It sounded like Junio was slightly unclear about the intent of the
wording in Patch 1. Not sure if my answer (in email) was sufficient or
if there are changes I should make to the patch.
* On Patch 5 of v3 (which is now patch 7 of v4), Junio suggested a course
of action to take with --keep-empty. I counter-proposed with a
--empty={drop,halt,keep} idea. Is just deferring this issue to a later
series okay, or are there changes I should make to the current series to
handle this? (If so, what changes should those be?)
Elijah Newren (9):
git-rebase.txt: document incompatible options
git-rebase.sh: update help messages a bit
t3422: new testcases for checking when incompatible options passed
git-rebase: error out when incompatible options passed
git-rebase.txt: address confusion between --no-ff vs --force-rebase
directory-rename-detection.txt: technical docs on abilities and
limitations
git-rebase.txt: document behavioral differences between modes
t3401: add directory rename testcases for rebase and am
git-rebase: make --allow-empty-message the default
Documentation/git-rebase.txt | 135 ++++++++++++++----
.../technical/directory-rename-detection.txt | 115 +++++++++++++++
git-rebase.sh | 43 +++++-
t/t3401-rebase-and-am-rename.sh | 105 ++++++++++++++
t/t3404-rebase-interactive.sh | 7 +-
t/t3405-rebase-malformed.sh | 11 +-
t/t3422-rebase-incompatible-options.sh | 88 ++++++++++++
7 files changed, 462 insertions(+), 42 deletions(-)
create mode 100644 Documentation/technical/directory-rename-detection.txt
create mode 100755 t/t3401-rebase-and-am-rename.sh
create mode 100755 t/t3422-rebase-incompatible-options.sh
1: 4cdf9130cc ! 1: 3f454ebc5e git-rebase.txt: document incompatible options
@@ -163,7 +163,7 @@
+implementations:
+
+ * one based on linkgit:git-am[1] (the default)
-+ * one based on linkgit:git-merge-recursive[1] (merge backend)
++ * one based on git-merge-recursive (merge backend)
+ * one based on linkgit:git-cherry-pick[1] (interactive backend)
+
+Flags only understood by the am backend:
2: e336f76c5e ! 2: 31a5a071a6 git-rebase.sh: update help messages a bit
@@ -6,6 +6,8 @@
to make like things (e.g. strategy and strategy-option) be near each
other.
+ Signed-off-by: Elijah Newren <newren@xxxxxxxxx>
+
diff --git a/git-rebase.sh b/git-rebase.sh
--- a/git-rebase.sh
+++ b/git-rebase.sh
3: 4ab38d8a5f ! 3: 5a2b5eec79 t3422: new testcases for checking when incompatible options passed
@@ -34,8 +34,7 @@
+ git commit -m A &&
+
+ git checkout B &&
-+ # This is indented with HT SP HT.
-+ echo " foo();" >>foo &&
++ echo "q qfoo();" | q_to_tab >>foo &&
+ git add foo &&
+ git commit -m B
+'
@@ -48,7 +47,7 @@
+# being ignored. Make sure rebase warns the user and aborts instead.
+#
+
-+test_run_rebase () {
++test_rebase_am_only () {
+ opt=$1
+ shift
+ test_expect_failure "$opt incompatible with --merge" "
@@ -78,10 +77,10 @@
+
+}
+
-+test_run_rebase --whitespace=fix
-+test_run_rebase --ignore-whitespace
-+test_run_rebase --committer-date-is-author-date
-+test_run_rebase -C4
++test_rebase_am_only --whitespace=fix
++test_rebase_am_only --ignore-whitespace
++test_rebase_am_only --committer-date-is-author-date
++test_rebase_am_only -C4
+
+test_expect_success '--preserve-merges incompatible with --signoff' '
+ git checkout B^0 &&
4: 5223954caf ! 4: 1e1c83724a git-rebase: error out when incompatible options passed
@@ -37,7 +37,8 @@
fi
+if test -n "$git_am_opt"; then
-+ incompatible_opts=$(echo "$git_am_opt" | sed -e 's/ -q//')
++ incompatible_opts=$(echo " $git_am_opt " | \
++ sed -e 's/ -q / /g' -e 's/^ \(.*\) $/\1/')
+ if test -n "$interactive_rebase"
+ then
+ if test -n "$incompatible_opts"
@@ -85,7 +86,7 @@
--- a/t/t3422-rebase-incompatible-options.sh
+++ b/t/t3422-rebase-incompatible-options.sh
@@
- test_run_rebase () {
+ test_rebase_am_only () {
opt=$1
shift
- test_expect_failure "$opt incompatible with --merge" "
5: 96f7ba98bc < --: ---------- git-rebase.txt: document behavioral inconsistencies between modes
6: 7bb7b380ac ! 5: 51023269d3 git-rebase.txt: address confusion between --no-ff vs --force-rebase
@@ -93,15 +93,3 @@
INCOMPATIBLE OPTIONS
--------------------
-@@
- BEHAVIORAL INCONSISTENCIES
- --------------------------
-
-- * --no-ff vs. --force-rebase
--
-- These options are actually identical, though their description
-- leads people to believe they might not be.
--
- * empty commits:
-
- am-based rebase will drop any "empty" commits, whether the
--: ---------- > 6: f017d45dd9 directory-rename-detection.txt: technical docs on abilities and limitations
--: ---------- > 7: 0a359df404 git-rebase.txt: document behavioral differences between modes
--: ---------- > 8: beaadceaef t3401: add directory rename testcases for rebase and am
7: 3ed07548a6 ! 9: 431b2c36d5 git-rebase: make --allow-empty-message the default
@@ -2,13 +2,85 @@
git-rebase: make --allow-empty-message the default
- All rebase backends should behave the same with empty commit messages, but
- currently do not. am-based rebases already apply commits with an empty
- commit message without stopping or requiring the user to specify an extra
- flag. Since am-based rebases are the default rebase type, and since it
- appears no one has ever requested a --no-allow-empty-message flag to
- change this behavior, make --allow-empty-message the default so that
- merge-based and interactive-based rebases will behave the same.
+ 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@xxxxxxxxx>
@@ -16,7 +88,7 @@
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@
- The --keep-empty option exists for interactive rebases to allow
+ The `--keep-empty` option exists for interactive rebases to allow
it to keep commits that started empty.
- * empty commit messages:
@@ -25,7 +97,7 @@
- messages.
-
- merge-based and interactive-based rebases will by default halt
-- on any such commits. The --allow-empty-message option exists to
+- on any such commits. The `--allow-empty-message` option exists to
- allow interactive-based rebases to apply such commits without
- halting.
-
--
2.18.0.9.g678597d97e
