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Teach rebase the --no-ff option.

For git-rebase.sh, --no-ff is a synonym for --force-rebase. For git-rebase--interactive.sh, --no-ff cherry-picks all the commits in the rebased branch, instead of fast-forwarding over any unchanged commits. --no-ff offers an alternative way to deal with reverted merges. Instead of "reverting the revert" you can use "rebase --no-ff" to recreate the branch with entirely new commits (they're new because at the very least the committer time is different). This obviates the need to revert the reversion, as you can re-merge the new topic branch directly. Added an addendum to revert-a-faulty-merge.txt describing the situation and how to use --no-ff to handle it. Signed-off-by: Marc Branchaud <marcnarc@xiplink.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Marc Branchaud committed Mar 24, 2010 at 16:34 UTC b499549401cb2b1f6c30d09681380fd519938eb0

5 files changed +152 -10

Documentation/git-rebase.txt

+21 -2

@@ -274,9 +274,16 @@ which makes little sense.

274 -f::

275 --force-rebase::

276 Force the rebase even if the current branch is a descendant

277 - of the commit you are rebasing onto. Normally the command will

277 + of the commit you are rebasing onto. Normally non-interactive rebase will

278 exit with the message "Current branch is up to date" in such a

279 situation.

280 + Incompatible with the --interactive option.

281 ++

282 +You may find this (or --no-ff with an interactive rebase) helpful after

283 +reverting a topic branch merge, as this option recreates the topic branch with

284 +fresh commits so it can be remerged successfully without needing to "revert

285 +the reversion" (see the

286 +link:howto/revert-a-faulty-merge.txt[revert-a-faulty-merge How-To] for details).

287

288 --ignore-whitespace::

289 --whitespace=<option>::

@@ -316,7 +323,19 @@ which makes little sense.

323 commit to be modified, and change the action of the moved

324 commit from `pick` to `squash` (or `fixup`).

325 +

319 -This option is only valid when '--interactive' option is used.

326 +This option is only valid when the '--interactive' option is used.

327 +

328 +--no-ff::

329 + With --interactive, cherry-pick all rebased commits instead of

330 + fast-forwarding over the unchanged ones. This ensures that the

331 + entire history of the rebased branch is composed of new commits.

332 ++

333 +Without --interactive, this is a synonym for --force-rebase.

334 ++

335 +You may find this helpful after reverting a topic branch merge, as this option

336 +recreates the topic branch with fresh commits so it can be remerged

337 +successfully without needing to "revert the reversion" (see the

338 +link:howto/revert-a-faulty-merge.txt[revert-a-faulty-merge How-To] for details).

339

340 include::merge-strategies.txt[]

341

Documentation/howto/revert-a-faulty-merge.txt

+90

@@ -142,6 +142,8 @@ different resolution strategies:

142 revert of a merge was rebuilt from scratch (i.e. rebasing and fixing,

143 as you seem to have interpreted), then re-merging the result without

144 doing anything else fancy would be the right thing to do.

145 + (See the ADDENDUM below for how to rebuild a branch from scratch

146 + without changing its original branching-off point.)

147

148 However, there are things to keep in mind when reverting a merge (and

149 reverting such a revert).

@@ -177,3 +179,91 @@ the answer is: "oops, I really shouldn't have merged it, because it wasn't

179 ready yet, and I really need to undo _all_ of the merge"). So then you

180 really should revert the merge, but when you want to re-do the merge, you

181 now need to do it by reverting the revert.

182 +

183 +ADDENDUM

184 +

185 +Sometimes you have to rewrite one of a topic branch's commits *and* you can't

186 +change the topic's branching-off point. Consider the following situation:

187 +

188 + P---o---o---M---x---x---W---x

189 + \ /

190 + A---B---C

191 +

192 +where commit W reverted commit M because it turned out that commit B was wrong

193 +and needs to be rewritten, but you need the rewritten topic to still branch

194 +from commit P (perhaps P is a branching-off point for yet another branch, and

195 +you want be able to merge the topic into both branches).

196 +

197 +The natural thing to do in this case is to checkout the A-B-C branch and use

198 +"rebase -i P" to change commit B. However this does not rewrite commit A,

199 +because "rebase -i" by default fast-forwards over any initial commits selected

200 +with the "pick" command. So you end up with this:

201 +

202 + P---o---o---M---x---x---W---x

203 + \ /

204 + A---B---C <-- old branch

205 + \

206 + B'---C' <-- naively rewritten branch

207 +

208 +To merge A-B'-C' into the mainline branch you would still have to first revert

209 +commit W in order to pick up the changes in A, but then it's likely that the

210 +changes in B' will conflict with the original B changes re-introduced by the

211 +reversion of W.

212 +

213 +However, you can avoid these problems if you recreate the entire branch,

214 +including commit A:

215 +

216 + A'---B'---C' <-- completely rewritten branch

217 + /

218 + P---o---o---M---x---x---W---x

219 + \ /

220 + A---B---C

221 +

222 +You can merge A'-B'-C' into the mainline branch without worrying about first

223 +reverting W. Mainline's history would look like this:

224 +

225 + A'---B'---C'------------------

226 + / \

227 + P---o---o---M---x---x---W---x---M2

228 + \ /

229 + A---B---C

230 +

231 +But if you don't actually need to change commit A, then you need some way to

232 +recreate it as a new commit with the same changes in it. The rebase commmand's

233 +--no-ff option provides a way to do this:

234 +

235 + $ git rebase [-i] --no-ff P

236 +

237 +The --no-ff option creates a new branch A'-B'-C' with all-new commits (all the

238 +SHA IDs will be different) even if in the interactive case you only actually

239 +modify commit B. You can then merge this new branch directly into the mainline

240 +branch and be sure you'll get all of the branch's changes.

241 +

242 +You can also use --no-ff in cases where you just add extra commits to the topic

243 +to fix it up. Let's revisit the situation discussed at the start of this howto:

244 +

245 + P---o---o---M---x---x---W---x

246 + \ /

247 + A---B---C----------------D---E <-- fixed-up topic branch

248 +

249 +At this point, you can use --no-ff to recreate the topic branch:

250 +

251 + $ git checkout E

252 + $ git rebase --no-ff P

253 +

254 +yielding

255 +

256 + A'---B'---C'------------D'---E' <-- recreated topic branch

257 + /

258 + P---o---o---M---x---x---W---x

259 + \ /

260 + A---B---C----------------D---E

261 +

262 +You can merge the recreated branch into the mainline without reverting commit W,

263 +and mainline's history will look like this:

264 +

265 + A'---B'---C'------------D'---E'

266 + / \

267 + P---o---o---M---x---x---W---x---M2

268 + \ /

269 + A---B---C

git-rebase--interactive.sh

+7 -2

@@ -20,6 +20,7 @@ v,verbose display a diffstat of what changed upstream

20 onto= rebase onto given branch instead of upstream

21 p,preserve-merges try to recreate merges instead of ignoring them

22 s,strategy= use the given merge strategy

23 +no-ff cherry-pick all commits, even if unchanged

24 m,merge always used (no-op)

25 i,interactive always used (no-op)

26 Actions:

@@ -103,6 +104,7 @@ VERBOSE=

104 OK_TO_SKIP_PRE_REBASE=

105 REBASE_ROOT=

106 AUTOSQUASH=

107 +NEVER_FF=

108

109 GIT_CHERRY_PICK_HELP=" After resolving the conflicts,

110 mark the corrected paths with 'git add <paths>', and

@@ -222,7 +224,7 @@ do_with_author () {

224 }

225

226 pick_one () {

225 - no_ff=

227 + no_ff=$NEVER_FF

228 case "$1" in -n) sha1=$2; no_ff=t ;; *) sha1=$1 ;; esac

229 output git rev-parse --verify $sha1 || die "Invalid commit name: $sha1"

230 test -d "$REWRITTEN" &&

@@ -742,6 +744,9 @@ first and then run 'git rebase --continue' again."

744 -i)

745 # yeah, we know

746 ;;

747 + --no-ff)

748 + NEVER_FF=t

749 + ;;

750 --root)

751 REBASE_ROOT=t

752 ;;

@@ -927,7 +932,7 @@ EOF

932 has_action "$TODO" ||

933 die_abort "Nothing to do"

934

930 - test -d "$REWRITTEN" || skip_unnecessary_picks

935 + test -d "$REWRITTEN" || test -n "$NEVER_FF" || skip_unnecessary_picks

936

937 git update-ref ORIG_HEAD $HEAD

938 output git checkout $ONTO && do_rest

git-rebase.sh

+2 -2

@@ -3,7 +3,7 @@

4 #

6 -USAGE='[--interactive | -i] [-v] [--force-rebase | -f] [--onto <newbase>] [<upstream>|--root] [<branch>] [--quiet | -q]'

6 +USAGE='[--interactive | -i] [-v] [--force-rebase | -f] [--no-ff] [--onto <newbase>] [<upstream>|--root] [<branch>] [--quiet | -q]'

7 LONG_USAGE='git-rebase replaces <branch> with a new branch of the

8 same name. When the --onto option is provided the new branch starts

9 out with a HEAD equal to <newbase>, otherwise it is equal to <upstream>

@@ -347,7 +347,7 @@ do

347 --root)

348 rebase_root=t

349 ;;

351 force_rebase=t

352 ;;

353 --rerere-autoupdate|--no-rerere-autoupdate)

t/t3404-rebase-interactive.sh

+32 -4

@@ -22,12 +22,18 @@ set_fake_editor

22 # | \

23 # | F - G - H (branch1)

24 # | \

25 -# \ I (branch2)

26 -# \

27 -# J - K - L - M (no-conflict-branch)

25 +# |\ I (branch2)

26 +# | \

27 +# | J - K - L - M (no-conflict-branch)

28 +# \

29 +# N - O - P (no-ff-branch)

30 #

31 # where A, B, D and G all touch file1, and one, two, three, four all

32 # touch file "conflict".

33 +#

34 +# WARNING: Modifications to the initial repository can change the SHA ID used

35 +# in the expect2 file for the 'stop on conflicting pick' test.

36 +

38 test_expect_success 'setup' '

39 test_commit A file1 &&

@@ -48,6 +54,11 @@ test_expect_success 'setup' '

54 done &&

55 git checkout -b no-conflict-branch A &&

56 for n in J K L M

57 + do

58 + test_commit $n file$n

59 + done &&

60 + git checkout -b no-ff-branch A &&

61 + for n in N O P

62 do

63 test_commit $n file$n

64 done

@@ -113,7 +124,7 @@ cat > expect2 << EOF

124 D

125 =======

126 G

116 ->>>>>>> 51047de... G

127 +>>>>>>> 5d18e54... G

128 EOF

129

130 test_expect_success 'stop on conflicting pick' '

@@ -553,4 +564,21 @@ test_expect_success 'reword' '

564 git show HEAD~2 | grep "C changed"

565 '

566

567 +test_tick # Ensure that the rebased commits get a different timestamp.

568 +test_expect_success 'always cherry-pick with --no-ff' '

569 + git checkout no-ff-branch &&

570 + git tag original-no-ff-branch &&

571 + git rebase -i --no-ff A &&

572 + touch empty &&

573 + for p in 0 1 2

574 + do

575 + test ! $(git rev-parse HEAD~$p) = $(git rev-parse original-no-ff-branch~$p) &&

576 + git diff HEAD~$p original-no-ff-branch~$p > out &&

577 + test_cmp empty out

578 + done &&

579 + test $(git rev-parse HEAD~3) = $(git rev-parse original-no-ff-branch~3) &&

580 + git diff HEAD~3 original-no-ff-branch~3 > out &&

581 + test_cmp empty out

582 +'

583 +

584 test_done