rebase: make the default backend configurable

index b393e1e9fe..0c2c569f95 100755
@@ -18,11 +18,8 @@ test_expect_success 'setup' '
 '
 
 test_expect_success 'rebase -m' '
-	git rebase -m master >report &&
-	>expect &&
-	sed -n -e "/^Already applied: /p" \
-		-e "/^Committed: /p" report >actual &&
-	test_cmp expect actual
+	git rebase -m master >actual &&
+	test_must_be_empty actual
 '
 
 test_expect_success 'rebase against master twice' '

index 1d0e2d27cc..ff32ca1080 100644
@@ -258,9 +258,25 @@ See also INCOMPATIBLE OPTIONS below.
 	original branch. The index and working tree are also left
 	unchanged as a result.
 
+--empty={drop,keep,ask}::
+	How to handle commits that become empty (because they contain a
+	subset of already upstream changes) or start empty.  With drop
+	(the default), commits that start or become empty are dropped.
+	With keep (implied by --exec), such commits are kept.  With ask
+	(implied by --interactive), the rebase will halt when an empty
+	commit is applied allowing you to choose whether to drop it or
+	commit it.  Also with ask, if the rebase is interactive then
+	commits which start empty will be commented out in the todo
+	action list (giving you a chance to uncomment).
++
+Note that this has no effect on commits which are already upstream (as
+can be checked via `git log --cherry-mark ...`), which are always
+dropped by rebase.
++
+See also INCOMPATIBLE OPTIONS below.
+
 --keep-empty::
-	Keep the commits that do not change anything from its
-	parents in the result.
+	Deprecated alias for what is now known as --empty=keep.
 +
 See also INCOMPATIBLE OPTIONS below.
 

@@ -569,6 +585,7 @@ are incompatible with the following options:
  * --interactive
  * --exec
  * --keep-empty
+ * --empty=
  * --edit-todo
  * --root when used in combination with --onto
 

@@ -580,6 +597,7 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --ignore-whitespace
  * --preserve-merges and --committer-date-is-author-date
  * --preserve-merges and --ignore-date
+ * --preserve-merges and --empty=
  * --keep-base and --onto
  * --keep-base and --root
 

@@ -588,19 +606,6 @@ BEHAVIORAL DIFFERENCES
 
 There are some subtle differences how the backends behave.
 
-Empty commits
-~~~~~~~~~~~~~
-
-The am backend drops any "empty" commits, regardless of whether the
-commit started empty (had no changes relative to its parent to
-start with) or ended empty (all changes were already applied
-upstream in other commits).
-
-The interactive backend drops commits by default that
-started empty and halts if it hits a commit that ended up empty.
-The `--keep-empty` option exists for the interactive backend to allow
-it to keep commits that started empty.
-
 Directory rename detection
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 

index 325072b0a3..d23e0bf778 100755
@@ -230,7 +230,7 @@ test_run_rebase () {
 test_run_rebase success ''
 test_run_rebase success -m
 test_run_rebase success -i
-test_have_prereq !REBASE_P || test_run_rebase failure -p
+test_have_prereq !REBASE_P || test_run_rebase success -p
 
 test_run_rebase () {
 	result=$1

@@ -245,7 +245,7 @@ test_run_rebase () {
 test_run_rebase success ''
 test_run_rebase success -m
 test_run_rebase success -i
-test_have_prereq !REBASE_P || test_run_rebase failure -p
+test_have_prereq !REBASE_P || test_run_rebase success -p
 test_run_rebase success --rebase-merges
 
 #       m

89 lines not on this page · raw message

index bec48e6a1f..468ebc1bef 100755
@@ -85,23 +85,27 @@ test_expect_failure REBASE_P 'Rebase -Xsubtree --keep-empty --preserve-merges --
 	verbose test "$(commit_message HEAD)" = "Empty commit"
 '
 
-test_expect_success 'Rebase -Xsubtree --keep-empty --onto commit' '
+test_expect_success 'Rebase -Xsubtree --empty=ask --onto commit' '
 	reset_rebase &&
 	git checkout -b rebase-onto to-rebase &&
-	test_must_fail git rebase -Xsubtree=files_subtree --keep-empty --onto files-master master &&
+	test_must_fail git rebase -Xsubtree=files_subtree --empty=ask --onto files-master master &&
 	: first pick results in no changes &&
-	git rebase --continue &&
+	test_must_fail git rebase --skip &&
+	: last pick was an empty commit that has no changes, but we want to keep it &&
+	git commit --allow-empty &&
 	verbose test "$(commit_message HEAD~2)" = "master4" &&
 	verbose test "$(commit_message HEAD~)" = "files_subtree/master5" &&
 	verbose test "$(commit_message HEAD)" = "Empty commit"
 '
 
-test_expect_success 'Rebase -Xsubtree --keep-empty --rebase-merges --onto commit' '
+test_expect_success 'Rebase -Xsubtree --empty=ask --rebase-merges --onto commit' '
 	reset_rebase &&
 	git checkout -b rebase-merges-onto to-rebase &&
-	test_must_fail git rebase -Xsubtree=files_subtree --keep-empty --rebase-merges --onto files-master --root &&
+	test_must_fail git rebase -Xsubtree=files_subtree --empty=ask --rebase-merges --onto files-master --root &&
 	: first pick results in no changes &&
-	git rebase --continue &&
+	test_must_fail git rebase --skip &&
+	: last pick was an empty commit that has no changes, but we want to keep it &&
+	git commit --allow-empty &&
 	verbose test "$(commit_message HEAD~2)" = "master4" &&
 	verbose test "$(commit_message HEAD~)" = "files_subtree/master5" &&
 	verbose test "$(commit_message HEAD)" = "Empty commit"

index 221b35f2df..79762b989a 100755
@@ -206,12 +206,18 @@ test_expect_success 'cherry-picked commits and fork-point work together' '
 	test_cmp expect D
 '
 
-test_expect_success 'rebase -q is quiet' '
+test_expect_success 'rebase --am -q is quiet' '
 	git checkout -b quiet topic &&
 	git rebase -q master >output.out 2>&1 &&
 	test_must_be_empty output.out
 '
 
+test_expect_success 'rebase --merge -q is quiet' '
+	git checkout -B quiet topic &&
+	git rebase --merge -q master >output.out 2>&1 &&
+	test_must_be_empty output.out
+'
+
 test_expect_success 'Rebase a commit that sprinkles CRs in' '
 	(
 		echo "One" &&

index 92f95b57da..3879a43fa0 100755
@@ -44,19 +44,16 @@ test_rebase_same_head_ () {
 	test_expect_$status "git rebase$flag $* with $changes is $what with $cmp HEAD" "
 		oldhead=\$(git rev-parse HEAD) &&
 		test_when_finished 'git reset --hard \$oldhead' &&
+		cp .git/logs/HEAD expect &&
 		git rebase$flag $* >stdout &&
 		if test $what = work
 		then
-			# Must check this case first, for 'is up to
-			# date, rebase forced[...]rewinding head' cases
-			test_i18ngrep 'rewinding head' stdout
+			wc -l .git/logs/HEAD >old &&
+			wc -l .git/logs/HEAD >new &&
+			test_line_count '-gt' $(($old + 2)) .git/logs/HEAD
 		elif test $what = noop
 		then
-			test_i18ngrep 'is up to date' stdout &&
-			test_i18ngrep ! 'rebase forced' stdout
-		elif test $what = noop-force
-		then
-			test_i18ngrep 'is up to date, rebase forced' stdout
+			test_cmp expect .git/logs/HEAD
 		fi &&
 		newhead=\$(git rev-parse HEAD) &&
 		if test $cmp = same

@@ -71,14 +68,14 @@ test_rebase_same_head_ () {
 
 changes='no changes'
 test_rebase_same_head success noop same success work same
-test_rebase_same_head success noop same success noop-force same master
-test_rebase_same_head success noop same success noop-force diff --onto B B
-test_rebase_same_head success noop same success noop-force diff --onto B... B
-test_rebase_same_head success noop same success noop-force same --onto master... master
-test_rebase_same_head success noop same success noop-force same --keep-base master
-test_rebase_same_head success noop same success noop-force same --keep-base
-test_rebase_same_head success noop same success noop-force same --no-fork-point
-test_rebase_same_head success noop same success noop-force same --keep-base --no-fork-point
+test_rebase_same_head success noop same success work same master
+test_rebase_same_head success noop same success work diff --onto B B
+test_rebase_same_head success noop same success work diff --onto B... B
+test_rebase_same_head success noop same success work same --onto master... master
+test_rebase_same_head success noop same success work same --keep-base master
+test_rebase_same_head success noop same success work same --keep-base
+test_rebase_same_head success noop same success work same --no-fork-point
+test_rebase_same_head success noop same success work same --keep-base --no-fork-point
 test_rebase_same_head success noop same success work same --fork-point master
 test_rebase_same_head success noop same success work diff --fork-point --onto B B
 test_rebase_same_head success noop same success work diff --fork-point --onto B... B

@@ -91,14 +88,14 @@ test_expect_success 'add work same to side' '
 
 changes='our changes'
 test_rebase_same_head success noop same success work same
-test_rebase_same_head success noop same success noop-force same master
-test_rebase_same_head success noop same success noop-force diff --onto B B
-test_rebase_same_head success noop same success noop-force diff --onto B... B
-test_rebase_same_head success noop same success noop-force same --onto master... master
-test_rebase_same_head success noop same success noop-force same --keep-base master
-test_rebase_same_head success noop same success noop-force same --keep-base
-test_rebase_same_head success noop same success noop-force same --no-fork-point
-test_rebase_same_head success noop same success noop-force same --keep-base --no-fork-point
+test_rebase_same_head success noop same success work same master
+test_rebase_same_head success noop same success work diff --onto B B
+test_rebase_same_head success noop same success work diff --onto B... B
+test_rebase_same_head success noop same success work same --onto master... master
+test_rebase_same_head success noop same success work same --keep-base master
+test_rebase_same_head success noop same success work same --keep-base
+test_rebase_same_head success noop same success work same --no-fork-point
+test_rebase_same_head success noop same success work same --keep-base --no-fork-point
 test_rebase_same_head success noop same success work same --fork-point master
 test_rebase_same_head success noop same success work diff --fork-point --onto B B
 test_rebase_same_head success noop same success work diff --fork-point --onto B... B

@@ -112,13 +109,13 @@ test_expect_success 'add work same to upstream' '
 '
 
 changes='our and their changes'
-test_rebase_same_head success noop same success noop-force diff --onto B B
-test_rebase_same_head success noop same success noop-force diff --onto B... B
+test_rebase_same_head success noop same success work diff --onto B B
+test_rebase_same_head success noop same success work diff --onto B... B
 test_rebase_same_head success noop same success work diff --onto master... master
 test_rebase_same_head success noop same success work diff --keep-base master
 test_rebase_same_head success noop same success work diff --keep-base
-test_rebase_same_head failure work same success work diff --fork-point --onto B B
-test_rebase_same_head failure work same success work diff --fork-point --onto B... B
+test_rebase_same_head success work same success work diff --fork-point --onto B B
+test_rebase_same_head success work same success work diff --fork-point --onto B... B
 test_rebase_same_head success noop same success work diff --fork-point --onto master... master
 test_rebase_same_head success noop same success work diff --fork-point --keep-base master
 

index 3879a43fa0..58c91c6899 100755
@@ -30,6 +30,8 @@ test_rebase_same_head () {
 	shift &&
 	test_rebase_same_head_ $status_n $what_n $cmp_n "" "$*" &&
 	test_rebase_same_head_ $status_f $what_f $cmp_f " --no-ff" "$*"
+	test_rebase_same_head_ $status_n $what_n $cmp_n " --merge" "$*" &&
+	test_rebase_same_head_ $status_f $what_f $cmp_f " --merge --no-ff" "$*"
 }
 
 test_rebase_same_head_ () {

index ff32ca1080..f1ace07c38 100644
@@ -409,13 +409,10 @@ your branch contains commits which were dropped, this option can be used
 with `--keep-base` in order to drop those commits from your branch.
 
 --ignore-whitespace::
-	Behaves differently depending on which backend is selected.
-+
-'am' backend: When applying a patch, ignore changes in whitespace in
-context lines if necessary.
-+
-'interactive' backend: Treat lines with only whitespace changes as
-unchanged for the sake of a three-way merge.
+	Ignore whitespace-only changes in the commits being rebased,
+	which may avoid "unnecessary" conflicts.  (Both backends
+	currently have differing edgecase bugs with this option; see
+	BEHAVIORAL DIFFERENCES.)
 
 --whitespace=<option>::
 	This flag is passed to the 'git apply' program

@@ -609,9 +606,94 @@ There are some subtle differences how the backends behave.
 Directory rename detection
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Directory rename heuristics are enabled in the merge and interactive
-backends.  Due to the lack of accurate tree information, directory
-rename detection is disabled in the am backend.
+Due to the lack of accurate tree information (arising from
+constructing fake ancestors with the limited information available in
+patches), directory rename detection is disabled in the am backend.
+Disabled directory rename detection means that if one side of history
+renames a directory and the other adds new files to the old directory,
+then the new files will be left behind in the old directory without
+any warning at the time of rebasing that you may want to move these
+files into the new directory.
+
+Directory rename detection works with the merge and interactive
+backends to provide you warnings in such cases.
+
+Context
+~~~~~~~
+
+The am backend works by creating a sequence of patches (by calling
+`format-patch` internally), and then applying the patches in sequence
+(calling `am` internally).  Patches are composed of multiple hunks,
+each with line numbers, a context region, and the actual changes.  The
+line numbers have to be taken with some fuzz, since the other side
+will likely have inserted or deleted lines earlier in the file.  The
+context region is meant to help find how to adjust the line numbers in
+order to apply the changes to the right lines.  However, if multiple
+areas of the code have the same surrounding lines of context, the
+wrong one can be picked.  There are real-world cases where this has
+caused commits to be reapplied incorrectly with no conflicts reported.
+Setting diff.context to a larger value may prevent such types of
+problems, but increases the chance of spurious conflicts (since it
+will require more lines of matching context to apply).
+
+The interactive backend works with a full copy of each relevant file,
+insulating it from these types of problems.
+
+Labelling of conflicts markers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When there are content conflicts, the merge machinery tries to
+annotate each side's conflict markers with the commits where the
+content came from.  Since the am backend drops the original
+information about the rebased commits and their parents (and instead
+generates new fake commits based off limited information in the
+generated patches), those commits cannot be identified; instead it has
+to fall back to a commit summary.  Also, when merge.conflictStyle is
+set to diff3, the am backend will use "constructed merge base" to
+label the content from the merge base, and thus provide no information
+about the merge base commit whatsoever.
+
+The interactive backend works with the full commits on both sides of
+history and thus has no such limitations.
+
+--ignore-whitespace
+~~~~~~~~~~~~~~~~~~~
+
+The --ignore-whitespace option is supposed to ignore whitespace-only
+changes if it allows the code to merge cleanly.  Unfortunately, the
+different backends implement this differently, and both have different
+edge case bugs.
++
+'am' backend: When applying a patch, ignore changes in whitespace in
+context lines if necessary.  (Which implies that if the whitespace
+change was not in the context lines but on a line with a real change,
+then the rebase will still fail with "unnecessary" content conflicts.)
++
+'interactive' backend: Treat lines with only whitespace changes as
+unchanged for the sake of a three-way merge.  This means that if one
+side made no changes and the commits being rebased had whitespace-only
+changes, those whitespaces fixups will be discarded despite the fact
+that they present no content conflict.
+
+Miscellaneous differences
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are a few more behavioral differences that most folks would
+probably consider inconsequential but which are mentioned for
+completeness:
+
+* Reflog: The two backends will use different wording when describing
+  the changes made in the reflog, though both will make use of the
+  word "rebase".
+
+* Progress, informational, and error messages: The two backends
+  provide slightly different progress and informational messages.
+  Also, the am backend writes error messages (such as "Your files
+  would be overwritten...") to stdout, while the interactive backend
+  writes them to stderr.
+
+* State directories: The two backends keep their state in different
+  directories under .git/
 
 include::merge-strategies.txt[]
 

index 5166f158dd..bd4d2d2f63 100755
@@ -10,9 +10,8 @@ test_description='tests to ensure compatibility between am and interactive backe
 GIT_AUTHOR_DATE="1999-04-02T08:03:20+05:30"
 export GIT_AUTHOR_DATE
 
-# This is a special case in which both am and interactive backends
-# provide the same output. It was done intentionally because
-# both the backends fall short of optimal behaviour.
+# This is a common case in which both am and interactive backends
+# provide the same output with --ignore-whitespace.
 test_expect_success 'setup' '
 	git checkout -b topic &&
 	q_to_tab >file <<-\EOF &&

index 71fd6396cd..0a491f2363 100755
@@ -183,19 +183,19 @@ test_expect_success 'default to common base in @{upstream}s reflog if no upstrea
 	test_cmp expect actual
 '
 
-test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg' '
+test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg (--am)' '
 	git checkout -B default-base master &&
 	git checkout -B default topic &&
 	git config branch.default.remote . &&
 	git config branch.default.merge refs/heads/default-base &&
-	git rebase &&
+	git rebase --am &&
 	git rev-parse --verify default-base >expect &&
 	git rev-parse default~1 >actual &&
 	test_cmp expect actual &&
 	git checkout default-base &&
 	git reset --hard HEAD^ &&
 	git checkout default &&
-	git rebase &&
+	git rebase --am &&
 	git rev-parse --verify default-base >expect &&
 	git rev-parse default~1 >actual &&
 	test_cmp expect actual

@@ -226,7 +226,7 @@ test_expect_success 'cherry-picked commits and fork-point work together' '
 
 test_expect_success 'rebase --am -q is quiet' '
 	git checkout -b quiet topic &&
-	git rebase -q master >output.out 2>&1 &&
+	git rebase --am -q master >output.out 2>&1 &&
 	test_must_be_empty output.out
 '
 

@@ -325,7 +325,7 @@ test_expect_success 'rebase --am and --show-current-patch' '
 		echo two >>init.t &&
 		git commit -a -m two &&
 		git tag two &&
-		test_must_fail git rebase -f --onto init HEAD^ &&
+		test_must_fail git rebase --am -f --onto init HEAD^ &&
 		GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
 		grep "show.*$(git rev-parse two)" stderr
 	)

index a0b9438b22..50803958fd 100755
@@ -52,13 +52,13 @@ test_expect_success 'rebase --interactive: directory rename detected' '
 	)
 '
 
-test_expect_failure 'rebase (am): directory rename detected' '
+test_expect_failure 'rebase --am: directory rename detected' '
 	(
 		cd dir-rename &&
 
 		git checkout B^0 &&
 
-		git -c merge.directoryRenames=true rebase A &&
+		git -c merge.directoryRenames=true rebase --am A &&
 
 		git ls-files -s >out &&
 		test_line_count = 5 out &&

index ae6e55ce79..743b7e511a 100755
@@ -1137,7 +1137,7 @@ test_expect_success C_LOCALE_OUTPUT 'rebase --edit-todo does not work on non-int
 	git checkout conflict-branch &&
 	(
 		set_fake_editor &&
-		test_must_fail git rebase -f --onto HEAD~2 HEAD~ &&
+		test_must_fail git rebase -f --am --onto HEAD~2 HEAD~ &&
 		test_must_fail git rebase --edit-todo
 	) &&
 	git rebase --abort

index 0c2c569f95..7ce617fc1f 100755
@@ -23,24 +23,24 @@ test_expect_success 'rebase -m' '
 '
 
 test_expect_success 'rebase against master twice' '
-	git rebase master >out &&
+	git rebase --am master >out &&
 	test_i18ngrep "Current branch topic is up to date" out
 '
 
 test_expect_success 'rebase against master twice with --force' '
-	git rebase --force-rebase master >out &&
+	git rebase --force-rebase --am master >out &&
 	test_i18ngrep "Current branch topic is up to date, rebase forced" out
 '
 
 test_expect_success 'rebase against master twice from another branch' '
 	git checkout topic^ &&
-	git rebase master topic >out &&
+	git rebase --am master topic >out &&
 	test_i18ngrep "Current branch topic is up to date" out
 '
 
 test_expect_success 'rebase fast-forward to master' '
 	git checkout topic^ &&
-	git rebase topic >out &&
+	git rebase --am topic >out &&
 	test_i18ngrep "Fast-forwarded HEAD to topic" out
 '
 

@@ -89,7 +89,7 @@ test_expect_success 'GIT_REFLOG_ACTION' '
 	git checkout -b reflog-topic start &&
 	test_commit reflog-to-rebase &&
 
-	git rebase reflog-onto &&
+	git rebase --am reflog-onto &&
 	git log -g --format=%gs -3 >actual &&
 	cat >expect <<-\EOF &&
 	rebase finished: returning to refs/heads/reflog-topic

@@ -99,7 +99,7 @@ test_expect_success 'GIT_REFLOG_ACTION' '
 	test_cmp expect actual &&
 
 	git checkout -b reflog-prefix reflog-to-rebase &&
-	GIT_REFLOG_ACTION=change-the-reflog git rebase reflog-onto &&
+	GIT_REFLOG_ACTION=change-the-reflog git rebase --am reflog-onto &&
 	git log -g --format=%gs -3 >actual &&
 	cat >expect <<-\EOF &&
 	rebase finished: returning to refs/heads/reflog-prefix

index 910f218284..3e31826170 100755
@@ -96,14 +96,14 @@ testrebase() {
 	'
 }
 
-testrebase "" .git/rebase-apply
+testrebase " --am" .git/rebase-apply
 testrebase " --merge" .git/rebase-merge
 
-test_expect_success 'rebase --quit' '
+test_expect_success 'rebase --am --quit' '
 	cd "$work_dir" &&
 	# Clean up the state from the previous one
 	git reset --hard pre-rebase &&
-	test_must_fail git rebase master &&
+	test_must_fail git rebase --am master &&
 	test_path_is_dir .git/rebase-apply &&
 	head_before=$(git rev-parse HEAD) &&
 	git rebase --quit &&

index 5f7e73cf83..3816159e20 100755
@@ -234,7 +234,7 @@ test_expect_success "rebase: noop rebase" '
 	git checkout feature-branch
 '
 
-testrebase "" .git/rebase-apply
+testrebase " --am" .git/rebase-apply
 testrebase " --merge" .git/rebase-merge
 testrebase " --interactive" .git/rebase-merge
 

index fd8efe84fe..19700b025b 100755
@@ -54,7 +54,7 @@ test_run_rebase () {
 		test_linear_range 'n o' e..
 	"
 }
-test_run_rebase success ''
+test_run_rebase success --am
 test_run_rebase success -m
 test_run_rebase success -i
 

@@ -70,7 +70,7 @@ test_run_rebase () {
 		test_linear_range "\'"$expected"\'" d..
 	"
 }
-test_run_rebase success 'n o e' ''
+test_run_rebase success 'n o e' --am
 test_run_rebase success 'n o e' -m
 test_run_rebase success 'n o e' -i
 

@@ -86,7 +86,7 @@ test_run_rebase () {
 		test_linear_range "\'"$expected"\'" c..
 	"
 }
-test_run_rebase success 'd n o e' ''
+test_run_rebase success 'd n o e' --am
 test_run_rebase success 'd n o e' -m
 test_run_rebase success 'd n o e' -i
 

@@ -102,7 +102,7 @@ test_run_rebase () {
 		test_linear_range "\'"$expected"\'" c..
 	"
 }
-test_run_rebase success 'd n o e' ''
+test_run_rebase success 'd n o e' --am
 test_run_rebase success 'd n o e' -m
 test_run_rebase success 'd n o e' -i
 

index 58c91c6899..b22aa8c7ee 100755
@@ -28,8 +28,8 @@ test_rebase_same_head () {
 	shift &&
 	cmp_f="$1" &&
 	shift &&
-	test_rebase_same_head_ $status_n $what_n $cmp_n "" "$*" &&
-	test_rebase_same_head_ $status_f $what_f $cmp_f " --no-ff" "$*"
+	test_rebase_same_head_ $status_n $what_n $cmp_n " --am" "$*" &&
+	test_rebase_same_head_ $status_f $what_f $cmp_f " --am --no-ff" "$*"
 	test_rebase_same_head_ $status_n $what_n $cmp_n " --merge" "$*" &&
 	test_rebase_same_head_ $status_f $what_f $cmp_f " --merge --no-ff" "$*"
 }

index bd4d2d2f63..a07e1f276b 100755
@@ -51,9 +51,9 @@ test_expect_success '--ignore-whitespace works with am backend' '
 	new line 2
 	line 3
 	EOF
-	test_must_fail git rebase main side &&
+	test_must_fail git rebase --am main side &&
 	git rebase --abort &&
-	git rebase --ignore-whitespace main side &&
+	git rebase --am --ignore-whitespace main side &&
 	test_cmp expect file
 '
 

@@ -71,7 +71,7 @@ test_expect_success '--ignore-whitespace works with interactive backend' '
 
 test_expect_success '--committer-date-is-author-date works with am backend' '
 	git commit --amend &&
-	git rebase --committer-date-is-author-date HEAD^ &&
+	git rebase --am --committer-date-is-author-date HEAD^ &&
 	git show HEAD --pretty="format:%ai" >authortime &&
 	git show HEAD --pretty="format:%ci" >committertime &&
 	test_cmp authortime committertime

@@ -103,7 +103,7 @@ test_expect_success '--committer-date-is-author-date works with rebase -r' '
 # sets to +0530.
 test_expect_success '--ignore-date works with am backend' '
 	git commit --amend --date="$GIT_AUTHOR_DATE" &&
-	git rebase --ignore-date HEAD^ &&
+	git rebase --am --ignore-date HEAD^ &&
 	git show HEAD --pretty="format:%ai" >authortime &&
 	grep "+0000" authortime
 '

index 7344253bfb..a8a73616e4 100755
@@ -53,10 +53,10 @@ test_expect_success 'git commit --amend --no-post-rewrite' '
 	test ! -f post-rewrite.data
 '
 
-test_expect_success 'git rebase' '
+test_expect_success 'git rebase --am' '
 	git reset --hard D &&
 	clear_hook_input &&
-	test_must_fail git rebase --onto A B &&
+	test_must_fail git rebase --am --onto A B &&
 	echo C > foo &&
 	git add foo &&
 	git rebase --continue &&

@@ -68,10 +68,10 @@ test_expect_success 'git rebase' '
 	verify_hook_input
 '
 
-test_expect_success 'git rebase --skip' '
+test_expect_success 'git rebase --am --skip' '
 	git reset --hard D &&
 	clear_hook_input &&
-	test_must_fail git rebase --onto A B &&
+	test_must_fail git rebase --am --onto A B &&
 	test_must_fail git rebase --skip &&
 	echo D > foo &&
 	git add foo &&

@@ -84,10 +84,10 @@ test_expect_success 'git rebase --skip' '
 	verify_hook_input
 '
 
-test_expect_success 'git rebase --skip the last one' '
+test_expect_success 'git rebase --am --skip the last one' '
 	git reset --hard F &&
 	clear_hook_input &&
-	test_must_fail git rebase --onto D A &&
+	test_must_fail git rebase --am --onto D A &&
 	git rebase --skip &&
 	echo rebase >expected.args &&
 	cat >expected.data <<-EOF &&

index 66d7a62797..d22b0acf2a 100755
@@ -71,10 +71,10 @@ test_expect_success 'prepare for rebase conflicts' '
 '
 
 
-test_expect_success 'status when rebase in progress before resolving conflicts' '
+test_expect_success 'status when rebase --am in progress before resolving conflicts' '
 	test_when_finished "git rebase --abort" &&
 	ONTO=$(git rev-parse --short HEAD^^) &&
-	test_must_fail git rebase HEAD^ --onto HEAD^^ &&
+	test_must_fail git rebase --am HEAD^ --onto HEAD^^ &&
 	cat >expected <<EOF &&
 rebase in progress; onto $ONTO
 You are currently rebasing branch '\''rebase_conflicts'\'' on '\''$ONTO'\''.

@@ -94,11 +94,11 @@ EOF
 '
 
 
-test_expect_success 'status when rebase in progress before rebase --continue' '
+test_expect_success 'status when rebase --am in progress before rebase --continue' '
 	git reset --hard rebase_conflicts &&
 	test_when_finished "git rebase --abort" &&
 	ONTO=$(git rev-parse --short HEAD^^) &&
-	test_must_fail git rebase HEAD^ --onto HEAD^^ &&
+	test_must_fail git rebase --am HEAD^ --onto HEAD^^ &&
 	echo three >main.txt &&
 	git add main.txt &&
 	cat >expected <<EOF &&

@@ -688,7 +688,7 @@ EOF
 '
 
 
-test_expect_success 'status when rebase conflicts with statushints disabled' '
+test_expect_success 'status when rebase --am conflicts with statushints disabled' '
 	git reset --hard master &&
 	git checkout -b statushints_disabled &&
 	test_when_finished "git config --local advice.statushints true" &&

@@ -698,7 +698,7 @@ test_expect_success 'status when rebase conflicts with statushints disabled' '
 	test_commit three_statushints main.txt three &&
 	test_when_finished "git rebase --abort" &&
 	ONTO=$(git rev-parse --short HEAD^^) &&
-	test_must_fail git rebase HEAD^ --onto HEAD^^ &&
+	test_must_fail git rebase --am HEAD^ --onto HEAD^^ &&
 	cat >expected <<EOF &&
 rebase in progress; onto $ONTO
 You are currently rebasing branch '\''statushints_disabled'\'' on '\''$ONTO'\''.

index 602d996a33..3fff6a06fa 100755
@@ -277,14 +277,27 @@ test_expect_success '--rebase' '
 	test_cmp expect actual
 '
 
-test_expect_success '--rebase fast forward' '
+test_expect_success '--rebase (merge) fast forward' '
 	git reset --hard before-rebase &&
 	git checkout -b ff &&
 	echo another modification >file &&
 	git commit -m third file &&
 
 	git checkout to-rebase &&
-	git pull --rebase . ff &&
+	git -c rebase.backend=merge pull --rebase . ff &&
+	test_cmp_rev HEAD ff &&
+
+	# The above only validates the result.  Did we actually bypass rebase?
+	git reflog -1 >reflog.actual &&
+	sed "s/^[0-9a-f][0-9a-f]*/OBJID/" reflog.actual >reflog.fuzzy &&
+	echo "OBJID HEAD@{0}: pull --rebase . ff: Fast-forward" >reflog.expected &&
+	test_cmp reflog.expected reflog.fuzzy
+'
+
+test_expect_success '--rebase (am) fast forward' '
+	git reset --hard before-rebase &&
+
+	git -c rebase.backend=am pull --rebase . ff &&
 	test_cmp_rev HEAD ff &&
 
 	# The above only validates the result.  Did we actually bypass rebase?

index 860542aad0..d383ce8130 100755
@@ -186,7 +186,7 @@ test_expect_success 'check multiple merge bases' '
 	)
 '
 
-test_expect_success 'rebase describes fake ancestor base' '
+test_expect_success 'rebase --merge describes parent of commit being picked' '
 	test_create_repo rebase &&
 	(
 		cd rebase &&

@@ -194,7 +194,16 @@ test_expect_success 'rebase describes fake ancestor base' '
 		test_commit master file &&
 		git checkout -b side HEAD^ &&
 		test_commit side file &&
-		test_must_fail git -c merge.conflictstyle=diff3 rebase master &&
+		test_must_fail git -c merge.conflictstyle=diff3 rebase --merge master &&
+		grep "||||||| parent of" file
+	)
+'
+
+test_expect_success 'rebase --am describes fake ancestor base' '
+	(
+		cd rebase &&
+		git rebase --abort &&
+		test_must_fail git -c merge.conflictstyle=diff3 rebase --am master &&
 		grep "||||||| constructed merge base" file
 	)
 '

index d98e32d812..e6ae30c999 100644
@@ -5,6 +5,14 @@ rebase.useBuiltin::
 	is always used. Setting this will emit a warning, to alert any
 	remaining users that setting this now does nothing.
 
+rebase.backend::
+	Default backend to use for rebasing.  Possible choices are
+	'am' or 'merge' (note that the merge backend is sometimes also
+	refered to as the interactive backend or the interactive
+	machinery elsewhere in the docs).  Also, in the future, if the
+	merge backend gains all remaining capabilities of the am
+	backend, this setting may become unused.
+
 rebase.stat::
 	Whether to show a diffstat of what changed upstream since the last
 	rebase. False by default.

index 1d510cd47b..3c81099d60 100644
@@ -440,7 +440,7 @@ __git_ps1 ()
 			__git_eread "$g/rebase-apply/last" total
 			if [ -f "$g/rebase-apply/rebasing" ]; then
 				__git_eread "$g/rebase-apply/head-name" b
-				r="|REBASE"
+				r="|REBASE-a"
 			elif [ -f "$g/rebase-apply/applying" ]; then
 				r="|AM"
 			else

index 88bc733ad6..8da5b1aee2 100755
@@ -189,11 +189,11 @@ test_expect_success 'prompt - rebase merge' '
 	test_cmp expected "$actual"
 '
 
-test_expect_success 'prompt - rebase' '
-	printf " (b2|REBASE 1/3)" >expected &&
+test_expect_success 'prompt - rebase am' '
+	printf " (b2|REBASE-a 1/3)" >expected &&
 	git checkout b2 &&
 	test_when_finished "git checkout master" &&
-	test_must_fail git rebase b1 b2 &&
+	test_must_fail git rebase --am b1 b2 &&
 	test_when_finished "git rebase --abort" &&
 	__git_ps1 >"$actual" &&
 	test_cmp expected "$actual"

index 79762b989a..71fd6396cd 100755
@@ -165,11 +165,29 @@ test_expect_success 'rebase works with format.useAutoBase' '
 	git rebase master
 '
 
-test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg' '
+test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg (--merge)' '
 	git checkout -b default-base master &&
 	git checkout -b default topic &&
 	git config branch.default.remote . &&
 	git config branch.default.merge refs/heads/default-base &&
+	git rebase --merge &&
+	git rev-parse --verify default-base >expect &&
+	git rev-parse default~1 >actual &&
+	test_cmp expect actual &&
+	git checkout default-base &&
+	git reset --hard HEAD^ &&
+	git checkout default &&
+	git rebase --merge &&
+	git rev-parse --verify default-base >expect &&
+	git rev-parse default~1 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg' '
+	git checkout -B default-base master &&
+	git checkout -B default topic &&
+	git config branch.default.remote . &&
+	git config branch.default.merge refs/heads/default-base &&
 	git rebase &&
 	git rev-parse --verify default-base >expect &&
 	git rev-parse default~1 >actual &&

index cf1ac2e359..e819889a31 100644
@@ -309,7 +309,7 @@ See also INCOMPATIBLE OPTIONS below.
 --merge::
 	Use merging strategies to rebase.  When the recursive (default) merge
 	strategy is used, this allows rebase to be aware of renames on the
-	upstream side.
+	upstream side.  This is the default.
 +
 Note that a rebase merge works by replaying each commit from the working
 branch on top of the <upstream> branch.  Because of this, when a merge

index 3fff6a06fa..4f9e7f7ff6 100755
@@ -340,7 +340,7 @@ test_expect_success '--rebase with conflicts shows advice' '
 	test_tick &&
 	git commit -m "Create conflict" seq.txt &&
 	test_must_fail git pull --rebase . seq 2>err >out &&
-	test_i18ngrep "Resolve all conflicts manually" out
+	test_i18ngrep "Resolve all conflicts manually" err
 '
 
 test_expect_success 'failed --rebase shows advice' '

@@ -354,7 +354,7 @@ test_expect_success 'failed --rebase shows advice' '
 	git checkout -f -b fails-to-rebase HEAD^ &&
 	test_commit v2-without-cr file "2" file2-lf &&
 	test_must_fail git pull --rebase . diverging 2>err >out &&
-	test_i18ngrep "Resolve all conflicts manually" out
+	test_i18ngrep "Resolve all conflicts manually" err
 '
 
 test_expect_success '--rebase fails with multiple branches' '

@@ -774,8 +774,10 @@ test_expect_success 'git pull --rebase does not reapply old patches' '
 	(
 		cd dst &&
 		test_must_fail git pull --rebase &&
-		find .git/rebase-apply -name "000*" >patches &&
-		test_line_count = 1 patches
+		cat .git/rebase-merge/done .git/rebase-merge/git-rebase-todo >work &&
+		grep -v -e \# -e ^$ work >patches &&
+		test_line_count = 1 patches &&
+		rm -f work
 	)
 '
 

index dbe8deac0d..aec45bca3b 100755
@@ -92,7 +92,8 @@ test_expect_success 'multiple dcommit from git svn will not clobber svn' "
 
 
 test_expect_success 'check that rebase really failed' '
-	test -d .git/rebase-apply
+	git status >output &&
+	grep currently.rebasing output
 '
 
 test_expect_success 'resolve, continue the rebase and dcommit' "

index f1ace07c38..cf1ac2e359 100644
@@ -258,6 +258,13 @@ See also INCOMPATIBLE OPTIONS below.
 	original branch. The index and working tree are also left
 	unchanged as a result.
 
+--am:
+	Use git-am internally to rebase.  This option may become a
+	no-op in the future once the interactive backend handles
+	everything the am one does.
++
+See also INCOMPATIBLE OPTIONS below.
+
 --empty={drop,keep,ask}::
 	How to handle commits that become empty (because they contain a
 	subset of already upstream changes) or start empty.  With drop

@@ -372,7 +379,7 @@ See also INCOMPATIBLE OPTIONS below.
 	Ensure at least <n> lines of surrounding context match before
 	and after each change.  When fewer lines of surrounding
 	context exist they all must match.  By default no context is
-	ever ignored.
+	ever ignored.  Implies --am.
 +
 See also INCOMPATIBLE OPTIONS below.
 

@@ -417,6 +424,7 @@ with `--keep-base` in order to drop those commits from your branch.
 --whitespace=<option>::
 	This flag is passed to the 'git apply' program
 	(see linkgit:git-apply[1]) that applies the patch.
+	Implies --am.
 +
 See also INCOMPATIBLE OPTIONS below.
 

@@ -567,6 +575,7 @@ INCOMPATIBLE OPTIONS
 
 The following options:
 
+ * --am
  * --whitespace
  * -C
 

index b393e1e9fe..0c2c569f95 100755
@@ -18,11 +18,8 @@ test_expect_success 'setup' '
 '
 
 test_expect_success 'rebase -m' '
-	git rebase -m master >report &&
-	>expect &&
-	sed -n -e "/^Already applied: /p" \
-		-e "/^Committed: /p" report >actual &&
-	test_cmp expect actual
+	git rebase -m master >actual &&
+	test_must_be_empty actual
 '
 
 test_expect_success 'rebase against master twice' '

index 1d0e2d27cc..ff32ca1080 100644
@@ -258,9 +258,25 @@ See also INCOMPATIBLE OPTIONS below.
 	original branch. The index and working tree are also left
 	unchanged as a result.
 
+--empty={drop,keep,ask}::
+	How to handle commits that become empty (because they contain a
+	subset of already upstream changes) or start empty.  With drop
+	(the default), commits that start or become empty are dropped.
+	With keep (implied by --exec), such commits are kept.  With ask
+	(implied by --interactive), the rebase will halt when an empty
+	commit is applied allowing you to choose whether to drop it or
+	commit it.  Also with ask, if the rebase is interactive then
+	commits which start empty will be commented out in the todo
+	action list (giving you a chance to uncomment).
++
+Note that this has no effect on commits which are already upstream (as
+can be checked via `git log --cherry-mark ...`), which are always
+dropped by rebase.
++
+See also INCOMPATIBLE OPTIONS below.
+
 --keep-empty::
-	Keep the commits that do not change anything from its
-	parents in the result.
+	Deprecated alias for what is now known as --empty=keep.
 +
 See also INCOMPATIBLE OPTIONS below.
 

@@ -569,6 +585,7 @@ are incompatible with the following options:
  * --interactive
  * --exec
  * --keep-empty
+ * --empty=
  * --edit-todo
  * --root when used in combination with --onto
 

@@ -580,6 +597,7 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --ignore-whitespace
  * --preserve-merges and --committer-date-is-author-date
  * --preserve-merges and --ignore-date
+ * --preserve-merges and --empty=
  * --keep-base and --onto
  * --keep-base and --root
 

@@ -588,19 +606,6 @@ BEHAVIORAL DIFFERENCES
 
 There are some subtle differences how the backends behave.
 
-Empty commits
-~~~~~~~~~~~~~
-
-The am backend drops any "empty" commits, regardless of whether the
-commit started empty (had no changes relative to its parent to
-start with) or ended empty (all changes were already applied
-upstream in other commits).
-
-The interactive backend drops commits by default that
-started empty and halts if it hits a commit that ended up empty.
-The `--keep-empty` option exists for the interactive backend to allow
-it to keep commits that started empty.
-
 Directory rename detection
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 

index 325072b0a3..d23e0bf778 100755
@@ -230,7 +230,7 @@ test_run_rebase () {
 test_run_rebase success ''
 test_run_rebase success -m
 test_run_rebase success -i
-test_have_prereq !REBASE_P || test_run_rebase failure -p
+test_have_prereq !REBASE_P || test_run_rebase success -p
 
 test_run_rebase () {
 	result=$1

@@ -245,7 +245,7 @@ test_run_rebase () {
 test_run_rebase success ''
 test_run_rebase success -m
 test_run_rebase success -i
-test_have_prereq !REBASE_P || test_run_rebase failure -p
+test_have_prereq !REBASE_P || test_run_rebase success -p
 test_run_rebase success --rebase-merges
 
 #       m

89 lines not on this page · raw message

index bec48e6a1f..468ebc1bef 100755
@@ -85,23 +85,27 @@ test_expect_failure REBASE_P 'Rebase -Xsubtree --keep-empty --preserve-merges --
 	verbose test "$(commit_message HEAD)" = "Empty commit"
 '
 
-test_expect_success 'Rebase -Xsubtree --keep-empty --onto commit' '
+test_expect_success 'Rebase -Xsubtree --empty=ask --onto commit' '
 	reset_rebase &&
 	git checkout -b rebase-onto to-rebase &&
-	test_must_fail git rebase -Xsubtree=files_subtree --keep-empty --onto files-master master &&
+	test_must_fail git rebase -Xsubtree=files_subtree --empty=ask --onto files-master master &&
 	: first pick results in no changes &&
-	git rebase --continue &&
+	test_must_fail git rebase --skip &&
+	: last pick was an empty commit that has no changes, but we want to keep it &&
+	git commit --allow-empty &&
 	verbose test "$(commit_message HEAD~2)" = "master4" &&
 	verbose test "$(commit_message HEAD~)" = "files_subtree/master5" &&
 	verbose test "$(commit_message HEAD)" = "Empty commit"
 '
 
-test_expect_success 'Rebase -Xsubtree --keep-empty --rebase-merges --onto commit' '
+test_expect_success 'Rebase -Xsubtree --empty=ask --rebase-merges --onto commit' '
 	reset_rebase &&
 	git checkout -b rebase-merges-onto to-rebase &&
-	test_must_fail git rebase -Xsubtree=files_subtree --keep-empty --rebase-merges --onto files-master --root &&
+	test_must_fail git rebase -Xsubtree=files_subtree --empty=ask --rebase-merges --onto files-master --root &&
 	: first pick results in no changes &&
-	git rebase --continue &&
+	test_must_fail git rebase --skip &&
+	: last pick was an empty commit that has no changes, but we want to keep it &&
+	git commit --allow-empty &&
 	verbose test "$(commit_message HEAD~2)" = "master4" &&
 	verbose test "$(commit_message HEAD~)" = "files_subtree/master5" &&
 	verbose test "$(commit_message HEAD)" = "Empty commit"

index 221b35f2df..79762b989a 100755
@@ -206,12 +206,18 @@ test_expect_success 'cherry-picked commits and fork-point work together' '
 	test_cmp expect D
 '
 
-test_expect_success 'rebase -q is quiet' '
+test_expect_success 'rebase --am -q is quiet' '
 	git checkout -b quiet topic &&
 	git rebase -q master >output.out 2>&1 &&
 	test_must_be_empty output.out
 '
 
+test_expect_success 'rebase --merge -q is quiet' '
+	git checkout -B quiet topic &&
+	git rebase --merge -q master >output.out 2>&1 &&
+	test_must_be_empty output.out
+'
+
 test_expect_success 'Rebase a commit that sprinkles CRs in' '
 	(
 		echo "One" &&

index ff32ca1080..f1ace07c38 100644
@@ -409,13 +409,10 @@ your branch contains commits which were dropped, this option can be used
 with `--keep-base` in order to drop those commits from your branch.
 
 --ignore-whitespace::
-	Behaves differently depending on which backend is selected.
-+
-'am' backend: When applying a patch, ignore changes in whitespace in
-context lines if necessary.
-+
-'interactive' backend: Treat lines with only whitespace changes as
-unchanged for the sake of a three-way merge.
+	Ignore whitespace-only changes in the commits being rebased,
+	which may avoid "unnecessary" conflicts.  (Both backends
+	currently have differing edgecase bugs with this option; see
+	BEHAVIORAL DIFFERENCES.)
 
 --whitespace=<option>::
 	This flag is passed to the 'git apply' program

@@ -609,9 +606,94 @@ There are some subtle differences how the backends behave.
 Directory rename detection
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Directory rename heuristics are enabled in the merge and interactive
-backends.  Due to the lack of accurate tree information, directory
-rename detection is disabled in the am backend.
+Due to the lack of accurate tree information (arising from
+constructing fake ancestors with the limited information available in
+patches), directory rename detection is disabled in the am backend.
+Disabled directory rename detection means that if one side of history
+renames a directory and the other adds new files to the old directory,
+then the new files will be left behind in the old directory without
+any warning at the time of rebasing that you may want to move these
+files into the new directory.
+
+Directory rename detection works with the merge and interactive
+backends to provide you warnings in such cases.
+
+Context
+~~~~~~~
+
+The am backend works by creating a sequence of patches (by calling
+`format-patch` internally), and then applying the patches in sequence
+(calling `am` internally).  Patches are composed of multiple hunks,
+each with line numbers, a context region, and the actual changes.  The
+line numbers have to be taken with some fuzz, since the other side
+will likely have inserted or deleted lines earlier in the file.  The
+context region is meant to help find how to adjust the line numbers in
+order to apply the changes to the right lines.  However, if multiple
+areas of the code have the same surrounding lines of context, the
+wrong one can be picked.  There are real-world cases where this has
+caused commits to be reapplied incorrectly with no conflicts reported.
+Setting diff.context to a larger value may prevent such types of
+problems, but increases the chance of spurious conflicts (since it
+will require more lines of matching context to apply).
+
+The interactive backend works with a full copy of each relevant file,
+insulating it from these types of problems.
+
+Labelling of conflicts markers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When there are content conflicts, the merge machinery tries to
+annotate each side's conflict markers with the commits where the
+content came from.  Since the am backend drops the original
+information about the rebased commits and their parents (and instead
+generates new fake commits based off limited information in the
+generated patches), those commits cannot be identified; instead it has
+to fall back to a commit summary.  Also, when merge.conflictStyle is
+set to diff3, the am backend will use "constructed merge base" to
+label the content from the merge base, and thus provide no information
+about the merge base commit whatsoever.
+
+The interactive backend works with the full commits on both sides of
+history and thus has no such limitations.
+
+--ignore-whitespace
+~~~~~~~~~~~~~~~~~~~
+
+The --ignore-whitespace option is supposed to ignore whitespace-only
+changes if it allows the code to merge cleanly.  Unfortunately, the
+different backends implement this differently, and both have different
+edge case bugs.
++
+'am' backend: When applying a patch, ignore changes in whitespace in
+context lines if necessary.  (Which implies that if the whitespace
+change was not in the context lines but on a line with a real change,
+then the rebase will still fail with "unnecessary" content conflicts.)
++
+'interactive' backend: Treat lines with only whitespace changes as
+unchanged for the sake of a three-way merge.  This means that if one
+side made no changes and the commits being rebased had whitespace-only
+changes, those whitespaces fixups will be discarded despite the fact
+that they present no content conflict.
+
+Miscellaneous differences
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are a few more behavioral differences that most folks would
+probably consider inconsequential but which are mentioned for
+completeness:
+
+* Reflog: The two backends will use different wording when describing
+  the changes made in the reflog, though both will make use of the
+  word "rebase".
+
+* Progress, informational, and error messages: The two backends
+  provide slightly different progress and informational messages.
+  Also, the am backend writes error messages (such as "Your files
+  would be overwritten...") to stdout, while the interactive backend
+  writes them to stderr.
+
+* State directories: The two backends keep their state in different
+  directories under .git/
 
 include::merge-strategies.txt[]
 

index 5166f158dd..bd4d2d2f63 100755
@@ -10,9 +10,8 @@ test_description='tests to ensure compatibility between am and interactive backe
 GIT_AUTHOR_DATE="1999-04-02T08:03:20+05:30"
 export GIT_AUTHOR_DATE
 
-# This is a special case in which both am and interactive backends
-# provide the same output. It was done intentionally because
-# both the backends fall short of optimal behaviour.
+# This is a common case in which both am and interactive backends
+# provide the same output with --ignore-whitespace.
 test_expect_success 'setup' '
 	git checkout -b topic &&
 	q_to_tab >file <<-\EOF &&

index 79762b989a..71fd6396cd 100755
@@ -165,11 +165,29 @@ test_expect_success 'rebase works with format.useAutoBase' '
 	git rebase master
 '
 
-test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg' '
+test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg (--merge)' '
 	git checkout -b default-base master &&
 	git checkout -b default topic &&
 	git config branch.default.remote . &&
 	git config branch.default.merge refs/heads/default-base &&
+	git rebase --merge &&
+	git rev-parse --verify default-base >expect &&
+	git rev-parse default~1 >actual &&
+	test_cmp expect actual &&
+	git checkout default-base &&
+	git reset --hard HEAD^ &&
+	git checkout default &&
+	git rebase --merge &&
+	git rev-parse --verify default-base >expect &&
+	git rev-parse default~1 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg' '
+	git checkout -B default-base master &&
+	git checkout -B default topic &&
+	git config branch.default.remote . &&
+	git config branch.default.merge refs/heads/default-base &&
 	git rebase &&
 	git rev-parse --verify default-base >expect &&
 	git rev-parse default~1 >actual &&

index 7432c0e241..40388ccf9f 100755
@@ -30,6 +30,8 @@ test_rebase_same_head () {
 	shift &&
 	test_rebase_same_head_ $status_n $what_n $cmp_n "" "$*" &&
 	test_rebase_same_head_ $status_f $what_f $cmp_f " --no-ff" "$*"
+	test_rebase_same_head_ $status_n $what_n $cmp_n " --merge" "$*" &&
+	test_rebase_same_head_ $status_f $what_f $cmp_f " --merge --no-ff" "$*"
 }
 
 test_rebase_same_head_ () {

index 92f95b57da..7432c0e241 100755
@@ -44,19 +44,15 @@ test_rebase_same_head_ () {
 	test_expect_$status "git rebase$flag $* with $changes is $what with $cmp HEAD" "
 		oldhead=\$(git rev-parse HEAD) &&
 		test_when_finished 'git reset --hard \$oldhead' &&
+		cp .git/logs/HEAD expect &&
 		git rebase$flag $* >stdout &&
 		if test $what = work
 		then
-			# Must check this case first, for 'is up to
-			# date, rebase forced[...]rewinding head' cases
-			test_i18ngrep 'rewinding head' stdout
+			old=\$(wc -l <expect) &&
+			test_line_count '-gt' \$old .git/logs/HEAD
 		elif test $what = noop
 		then
-			test_i18ngrep 'is up to date' stdout &&
-			test_i18ngrep ! 'rebase forced' stdout
-		elif test $what = noop-force
-		then
-			test_i18ngrep 'is up to date, rebase forced' stdout
+			test_cmp expect .git/logs/HEAD
 		fi &&
 		newhead=\$(git rev-parse HEAD) &&
 		if test $cmp = same

@@ -71,14 +67,14 @@ test_rebase_same_head_ () {
 
 changes='no changes'
 test_rebase_same_head success noop same success work same
-test_rebase_same_head success noop same success noop-force same master
-test_rebase_same_head success noop same success noop-force diff --onto B B
-test_rebase_same_head success noop same success noop-force diff --onto B... B
-test_rebase_same_head success noop same success noop-force same --onto master... master
-test_rebase_same_head success noop same success noop-force same --keep-base master
-test_rebase_same_head success noop same success noop-force same --keep-base
-test_rebase_same_head success noop same success noop-force same --no-fork-point
-test_rebase_same_head success noop same success noop-force same --keep-base --no-fork-point
+test_rebase_same_head success noop same success work same master
+test_rebase_same_head success noop same success work diff --onto B B
+test_rebase_same_head success noop same success work diff --onto B... B
+test_rebase_same_head success noop same success work same --onto master... master
+test_rebase_same_head success noop same success work same --keep-base master
+test_rebase_same_head success noop same success work same --keep-base
+test_rebase_same_head success noop same success work same --no-fork-point
+test_rebase_same_head success noop same success work same --keep-base --no-fork-point
 test_rebase_same_head success noop same success work same --fork-point master
 test_rebase_same_head success noop same success work diff --fork-point --onto B B
 test_rebase_same_head success noop same success work diff --fork-point --onto B... B

@@ -91,14 +87,14 @@ test_expect_success 'add work same to side' '
 
 changes='our changes'
 test_rebase_same_head success noop same success work same
-test_rebase_same_head success noop same success noop-force same master
-test_rebase_same_head success noop same success noop-force diff --onto B B
-test_rebase_same_head success noop same success noop-force diff --onto B... B
-test_rebase_same_head success noop same success noop-force same --onto master... master
-test_rebase_same_head success noop same success noop-force same --keep-base master
-test_rebase_same_head success noop same success noop-force same --keep-base
-test_rebase_same_head success noop same success noop-force same --no-fork-point
-test_rebase_same_head success noop same success noop-force same --keep-base --no-fork-point
+test_rebase_same_head success noop same success work same master
+test_rebase_same_head success noop same success work diff --onto B B
+test_rebase_same_head success noop same success work diff --onto B... B
+test_rebase_same_head success noop same success work same --onto master... master
+test_rebase_same_head success noop same success work same --keep-base master
+test_rebase_same_head success noop same success work same --keep-base
+test_rebase_same_head success noop same success work same --no-fork-point
+test_rebase_same_head success noop same success work same --keep-base --no-fork-point
 test_rebase_same_head success noop same success work same --fork-point master
 test_rebase_same_head success noop same success work diff --fork-point --onto B B
 test_rebase_same_head success noop same success work diff --fork-point --onto B... B

@@ -112,8 +108,8 @@ test_expect_success 'add work same to upstream' '
 '
 
 changes='our and their changes'
-test_rebase_same_head success noop same success noop-force diff --onto B B
-test_rebase_same_head success noop same success noop-force diff --onto B... B
+test_rebase_same_head success noop same success work diff --onto B B
+test_rebase_same_head success noop same success work diff --onto B... B
 test_rebase_same_head success noop same success work diff --onto master... master
 test_rebase_same_head success noop same success work diff --keep-base master
 test_rebase_same_head success noop same success work diff --keep-base

index d98e32d812..e6ae30c999 100644
@@ -5,6 +5,14 @@ rebase.useBuiltin::
 	is always used. Setting this will emit a warning, to alert any
 	remaining users that setting this now does nothing.
 
+rebase.backend::
+	Default backend to use for rebasing.  Possible choices are
+	'am' or 'merge' (note that the merge backend is sometimes also
+	refered to as the interactive backend or the interactive
+	machinery elsewhere in the docs).  Also, in the future, if the
+	merge backend gains all remaining capabilities of the am
+	backend, this setting may become unused.
+
 rebase.stat::
 	Whether to show a diffstat of what changed upstream since the last
 	rebase. False by default.

index 602d996a33..3fff6a06fa 100755
@@ -277,14 +277,27 @@ test_expect_success '--rebase' '
 	test_cmp expect actual
 '
 
-test_expect_success '--rebase fast forward' '
+test_expect_success '--rebase (merge) fast forward' '
 	git reset --hard before-rebase &&
 	git checkout -b ff &&
 	echo another modification >file &&
 	git commit -m third file &&
 
 	git checkout to-rebase &&
-	git pull --rebase . ff &&
+	git -c rebase.backend=merge pull --rebase . ff &&
+	test_cmp_rev HEAD ff &&
+
+	# The above only validates the result.  Did we actually bypass rebase?
+	git reflog -1 >reflog.actual &&
+	sed "s/^[0-9a-f][0-9a-f]*/OBJID/" reflog.actual >reflog.fuzzy &&
+	echo "OBJID HEAD@{0}: pull --rebase . ff: Fast-forward" >reflog.expected &&
+	test_cmp reflog.expected reflog.fuzzy
+'
+
+test_expect_success '--rebase (am) fast forward' '
+	git reset --hard before-rebase &&
+
+	git -c rebase.backend=am pull --rebase . ff &&
 	test_cmp_rev HEAD ff &&
 
 	# The above only validates the result.  Did we actually bypass rebase?

index 860542aad0..d383ce8130 100755
@@ -186,7 +186,7 @@ test_expect_success 'check multiple merge bases' '
 	)
 '
 
-test_expect_success 'rebase describes fake ancestor base' '
+test_expect_success 'rebase --merge describes parent of commit being picked' '
 	test_create_repo rebase &&
 	(
 		cd rebase &&

@@ -194,7 +194,16 @@ test_expect_success 'rebase describes fake ancestor base' '
 		test_commit master file &&
 		git checkout -b side HEAD^ &&
 		test_commit side file &&
-		test_must_fail git -c merge.conflictstyle=diff3 rebase master &&
+		test_must_fail git -c merge.conflictstyle=diff3 rebase --merge master &&
+		grep "||||||| parent of" file
+	)
+'
+
+test_expect_success 'rebase --am describes fake ancestor base' '
+	(
+		cd rebase &&
+		git rebase --abort &&
+		test_must_fail git -c merge.conflictstyle=diff3 rebase --am master &&
 		grep "||||||| constructed merge base" file
 	)
 '

index 71fd6396cd..0a491f2363 100755
@@ -183,19 +183,19 @@ test_expect_success 'default to common base in @{upstream}s reflog if no upstrea
 	test_cmp expect actual
 '
 
-test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg' '
+test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg (--am)' '
 	git checkout -B default-base master &&
 	git checkout -B default topic &&
 	git config branch.default.remote . &&
 	git config branch.default.merge refs/heads/default-base &&
-	git rebase &&
+	git rebase --am &&
 	git rev-parse --verify default-base >expect &&
 	git rev-parse default~1 >actual &&
 	test_cmp expect actual &&
 	git checkout default-base &&
 	git reset --hard HEAD^ &&
 	git checkout default &&
-	git rebase &&
+	git rebase --am &&
 	git rev-parse --verify default-base >expect &&
 	git rev-parse default~1 >actual &&
 	test_cmp expect actual

@@ -226,7 +226,7 @@ test_expect_success 'cherry-picked commits and fork-point work together' '
 
 test_expect_success 'rebase --am -q is quiet' '
 	git checkout -b quiet topic &&
-	git rebase -q master >output.out 2>&1 &&
+	git rebase --am -q master >output.out 2>&1 &&
 	test_must_be_empty output.out
 '
 

@@ -325,7 +325,7 @@ test_expect_success 'rebase --am and --show-current-patch' '
 		echo two >>init.t &&
 		git commit -a -m two &&
 		git tag two &&
-		test_must_fail git rebase -f --onto init HEAD^ &&
+		test_must_fail git rebase --am -f --onto init HEAD^ &&
 		GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
 		grep "show.*$(git rev-parse two)" stderr
 	)

index a0b9438b22..50803958fd 100755
@@ -52,13 +52,13 @@ test_expect_success 'rebase --interactive: directory rename detected' '
 	)
 '
 
-test_expect_failure 'rebase (am): directory rename detected' '
+test_expect_failure 'rebase --am: directory rename detected' '
 	(
 		cd dir-rename &&
 
 		git checkout B^0 &&
 
-		git -c merge.directoryRenames=true rebase A &&
+		git -c merge.directoryRenames=true rebase --am A &&
 
 		git ls-files -s >out &&
 		test_line_count = 5 out &&

index ae6e55ce79..743b7e511a 100755
@@ -1137,7 +1137,7 @@ test_expect_success C_LOCALE_OUTPUT 'rebase --edit-todo does not work on non-int
 	git checkout conflict-branch &&
 	(
 		set_fake_editor &&
-		test_must_fail git rebase -f --onto HEAD~2 HEAD~ &&
+		test_must_fail git rebase -f --am --onto HEAD~2 HEAD~ &&
 		test_must_fail git rebase --edit-todo
 	) &&
 	git rebase --abort

index 0c2c569f95..7ce617fc1f 100755
@@ -23,24 +23,24 @@ test_expect_success 'rebase -m' '
 '
 
 test_expect_success 'rebase against master twice' '
-	git rebase master >out &&
+	git rebase --am master >out &&
 	test_i18ngrep "Current branch topic is up to date" out
 '
 
 test_expect_success 'rebase against master twice with --force' '
-	git rebase --force-rebase master >out &&
+	git rebase --force-rebase --am master >out &&
 	test_i18ngrep "Current branch topic is up to date, rebase forced" out
 '
 
 test_expect_success 'rebase against master twice from another branch' '
 	git checkout topic^ &&
-	git rebase master topic >out &&
+	git rebase --am master topic >out &&
 	test_i18ngrep "Current branch topic is up to date" out
 '
 
 test_expect_success 'rebase fast-forward to master' '
 	git checkout topic^ &&
-	git rebase topic >out &&
+	git rebase --am topic >out &&
 	test_i18ngrep "Fast-forwarded HEAD to topic" out
 '
 

@@ -89,7 +89,7 @@ test_expect_success 'GIT_REFLOG_ACTION' '
 	git checkout -b reflog-topic start &&
 	test_commit reflog-to-rebase &&
 
-	git rebase reflog-onto &&
+	git rebase --am reflog-onto &&
 	git log -g --format=%gs -3 >actual &&
 	cat >expect <<-\EOF &&
 	rebase finished: returning to refs/heads/reflog-topic

@@ -99,7 +99,7 @@ test_expect_success 'GIT_REFLOG_ACTION' '
 	test_cmp expect actual &&
 
 	git checkout -b reflog-prefix reflog-to-rebase &&
-	GIT_REFLOG_ACTION=change-the-reflog git rebase reflog-onto &&
+	GIT_REFLOG_ACTION=change-the-reflog git rebase --am reflog-onto &&
 	git log -g --format=%gs -3 >actual &&
 	cat >expect <<-\EOF &&
 	rebase finished: returning to refs/heads/reflog-prefix

index 910f218284..3e31826170 100755
@@ -96,14 +96,14 @@ testrebase() {
 	'
 }
 
-testrebase "" .git/rebase-apply
+testrebase " --am" .git/rebase-apply
 testrebase " --merge" .git/rebase-merge
 
-test_expect_success 'rebase --quit' '
+test_expect_success 'rebase --am --quit' '
 	cd "$work_dir" &&
 	# Clean up the state from the previous one
 	git reset --hard pre-rebase &&
-	test_must_fail git rebase master &&
+	test_must_fail git rebase --am master &&
 	test_path_is_dir .git/rebase-apply &&
 	head_before=$(git rev-parse HEAD) &&
 	git rebase --quit &&

index 5f7e73cf83..3816159e20 100755
@@ -234,7 +234,7 @@ test_expect_success "rebase: noop rebase" '
 	git checkout feature-branch
 '
 
-testrebase "" .git/rebase-apply
+testrebase " --am" .git/rebase-apply
 testrebase " --merge" .git/rebase-merge
 testrebase " --interactive" .git/rebase-merge
 

index fd8efe84fe..19700b025b 100755
@@ -54,7 +54,7 @@ test_run_rebase () {
 		test_linear_range 'n o' e..
 	"
 }
-test_run_rebase success ''
+test_run_rebase success --am
 test_run_rebase success -m
 test_run_rebase success -i
 

@@ -70,7 +70,7 @@ test_run_rebase () {
 		test_linear_range "\'"$expected"\'" d..
 	"
 }
-test_run_rebase success 'n o e' ''
+test_run_rebase success 'n o e' --am
 test_run_rebase success 'n o e' -m
 test_run_rebase success 'n o e' -i
 

@@ -86,7 +86,7 @@ test_run_rebase () {
 		test_linear_range "\'"$expected"\'" c..
 	"
 }
-test_run_rebase success 'd n o e' ''
+test_run_rebase success 'd n o e' --am
 test_run_rebase success 'd n o e' -m
 test_run_rebase success 'd n o e' -i
 

@@ -102,7 +102,7 @@ test_run_rebase () {
 		test_linear_range "\'"$expected"\'" c..
 	"
 }
-test_run_rebase success 'd n o e' ''
+test_run_rebase success 'd n o e' --am
 test_run_rebase success 'd n o e' -m
 test_run_rebase success 'd n o e' -i
 

index 40388ccf9f..4b3cecce56 100755
@@ -28,8 +28,8 @@ test_rebase_same_head () {
 	shift &&
 	cmp_f="$1" &&
 	shift &&
-	test_rebase_same_head_ $status_n $what_n $cmp_n "" "$*" &&
-	test_rebase_same_head_ $status_f $what_f $cmp_f " --no-ff" "$*"
+	test_rebase_same_head_ $status_n $what_n $cmp_n " --am" "$*" &&
+	test_rebase_same_head_ $status_f $what_f $cmp_f " --am --no-ff" "$*"
 	test_rebase_same_head_ $status_n $what_n $cmp_n " --merge" "$*" &&
 	test_rebase_same_head_ $status_f $what_f $cmp_f " --merge --no-ff" "$*"
 }

index bd4d2d2f63..a07e1f276b 100755
@@ -51,9 +51,9 @@ test_expect_success '--ignore-whitespace works with am backend' '
 	new line 2
 	line 3
 	EOF
-	test_must_fail git rebase main side &&
+	test_must_fail git rebase --am main side &&
 	git rebase --abort &&
-	git rebase --ignore-whitespace main side &&
+	git rebase --am --ignore-whitespace main side &&
 	test_cmp expect file
 '
 

@@ -71,7 +71,7 @@ test_expect_success '--ignore-whitespace works with interactive backend' '
 
 test_expect_success '--committer-date-is-author-date works with am backend' '
 	git commit --amend &&
-	git rebase --committer-date-is-author-date HEAD^ &&
+	git rebase --am --committer-date-is-author-date HEAD^ &&
 	git show HEAD --pretty="format:%ai" >authortime &&
 	git show HEAD --pretty="format:%ci" >committertime &&
 	test_cmp authortime committertime

@@ -103,7 +103,7 @@ test_expect_success '--committer-date-is-author-date works with rebase -r' '
 # sets to +0530.
 test_expect_success '--ignore-date works with am backend' '
 	git commit --amend --date="$GIT_AUTHOR_DATE" &&
-	git rebase --ignore-date HEAD^ &&
+	git rebase --am --ignore-date HEAD^ &&
 	git show HEAD --pretty="format:%ai" >authortime &&
 	grep "+0000" authortime
 '

index 7344253bfb..a8a73616e4 100755
@@ -53,10 +53,10 @@ test_expect_success 'git commit --amend --no-post-rewrite' '
 	test ! -f post-rewrite.data
 '
 
-test_expect_success 'git rebase' '
+test_expect_success 'git rebase --am' '
 	git reset --hard D &&
 	clear_hook_input &&
-	test_must_fail git rebase --onto A B &&
+	test_must_fail git rebase --am --onto A B &&
 	echo C > foo &&
 	git add foo &&
 	git rebase --continue &&

@@ -68,10 +68,10 @@ test_expect_success 'git rebase' '
 	verify_hook_input
 '
 
-test_expect_success 'git rebase --skip' '
+test_expect_success 'git rebase --am --skip' '
 	git reset --hard D &&
 	clear_hook_input &&
-	test_must_fail git rebase --onto A B &&
+	test_must_fail git rebase --am --onto A B &&
 	test_must_fail git rebase --skip &&
 	echo D > foo &&
 	git add foo &&

@@ -84,10 +84,10 @@ test_expect_success 'git rebase --skip' '
 	verify_hook_input
 '
 
-test_expect_success 'git rebase --skip the last one' '
+test_expect_success 'git rebase --am --skip the last one' '
 	git reset --hard F &&
 	clear_hook_input &&
-	test_must_fail git rebase --onto D A &&
+	test_must_fail git rebase --am --onto D A &&
 	git rebase --skip &&
 	echo rebase >expected.args &&
 	cat >expected.data <<-EOF &&

index 66d7a62797..d22b0acf2a 100755
@@ -71,10 +71,10 @@ test_expect_success 'prepare for rebase conflicts' '
 '
 
 
-test_expect_success 'status when rebase in progress before resolving conflicts' '
+test_expect_success 'status when rebase --am in progress before resolving conflicts' '
 	test_when_finished "git rebase --abort" &&
 	ONTO=$(git rev-parse --short HEAD^^) &&
-	test_must_fail git rebase HEAD^ --onto HEAD^^ &&
+	test_must_fail git rebase --am HEAD^ --onto HEAD^^ &&
 	cat >expected <<EOF &&
 rebase in progress; onto $ONTO
 You are currently rebasing branch '\''rebase_conflicts'\'' on '\''$ONTO'\''.

@@ -94,11 +94,11 @@ EOF
 '
 
 
-test_expect_success 'status when rebase in progress before rebase --continue' '
+test_expect_success 'status when rebase --am in progress before rebase --continue' '
 	git reset --hard rebase_conflicts &&
 	test_when_finished "git rebase --abort" &&
 	ONTO=$(git rev-parse --short HEAD^^) &&
-	test_must_fail git rebase HEAD^ --onto HEAD^^ &&
+	test_must_fail git rebase --am HEAD^ --onto HEAD^^ &&
 	echo three >main.txt &&
 	git add main.txt &&
 	cat >expected <<EOF &&

@@ -688,7 +688,7 @@ EOF
 '
 
 
-test_expect_success 'status when rebase conflicts with statushints disabled' '
+test_expect_success 'status when rebase --am conflicts with statushints disabled' '
 	git reset --hard master &&
 	git checkout -b statushints_disabled &&
 	test_when_finished "git config --local advice.statushints true" &&

@@ -698,7 +698,7 @@ test_expect_success 'status when rebase conflicts with statushints disabled' '
 	test_commit three_statushints main.txt three &&
 	test_when_finished "git rebase --abort" &&
 	ONTO=$(git rev-parse --short HEAD^^) &&
-	test_must_fail git rebase HEAD^ --onto HEAD^^ &&
+	test_must_fail git rebase --am HEAD^ --onto HEAD^^ &&
 	cat >expected <<EOF &&
 rebase in progress; onto $ONTO
 You are currently rebasing branch '\''statushints_disabled'\'' on '\''$ONTO'\''.

index cf1ac2e359..e819889a31 100644
@@ -309,7 +309,7 @@ See also INCOMPATIBLE OPTIONS below.
 --merge::
 	Use merging strategies to rebase.  When the recursive (default) merge
 	strategy is used, this allows rebase to be aware of renames on the
-	upstream side.
+	upstream side.  This is the default.
 +
 Note that a rebase merge works by replaying each commit from the working
 branch on top of the <upstream> branch.  Because of this, when a merge

index 3fff6a06fa..4f9e7f7ff6 100755
@@ -340,7 +340,7 @@ test_expect_success '--rebase with conflicts shows advice' '
 	test_tick &&
 	git commit -m "Create conflict" seq.txt &&
 	test_must_fail git pull --rebase . seq 2>err >out &&
-	test_i18ngrep "Resolve all conflicts manually" out
+	test_i18ngrep "Resolve all conflicts manually" err
 '
 
 test_expect_success 'failed --rebase shows advice' '

@@ -354,7 +354,7 @@ test_expect_success 'failed --rebase shows advice' '
 	git checkout -f -b fails-to-rebase HEAD^ &&
 	test_commit v2-without-cr file "2" file2-lf &&
 	test_must_fail git pull --rebase . diverging 2>err >out &&
-	test_i18ngrep "Resolve all conflicts manually" out
+	test_i18ngrep "Resolve all conflicts manually" err
 '
 
 test_expect_success '--rebase fails with multiple branches' '

@@ -774,8 +774,10 @@ test_expect_success 'git pull --rebase does not reapply old patches' '
 	(
 		cd dst &&
 		test_must_fail git pull --rebase &&
-		find .git/rebase-apply -name "000*" >patches &&
-		test_line_count = 1 patches
+		cat .git/rebase-merge/done .git/rebase-merge/git-rebase-todo >work &&
+		grep -v -e \# -e ^$ work >patches &&
+		test_line_count = 1 patches &&
+		rm -f work
 	)
 '
 

index dbe8deac0d..aec45bca3b 100755
@@ -92,7 +92,8 @@ test_expect_success 'multiple dcommit from git svn will not clobber svn' "
 
 
 test_expect_success 'check that rebase really failed' '
-	test -d .git/rebase-apply
+	git status >output &&
+	grep currently.rebasing output
 '
 
 test_expect_success 'resolve, continue the rebase and dcommit' "

index f1ace07c38..cf1ac2e359 100644
@@ -258,6 +258,13 @@ See also INCOMPATIBLE OPTIONS below.
 	original branch. The index and working tree are also left
 	unchanged as a result.
 
+--am:
+	Use git-am internally to rebase.  This option may become a
+	no-op in the future once the interactive backend handles
+	everything the am one does.
++
+See also INCOMPATIBLE OPTIONS below.
+
 --empty={drop,keep,ask}::
 	How to handle commits that become empty (because they contain a
 	subset of already upstream changes) or start empty.  With drop

@@ -372,7 +379,7 @@ See also INCOMPATIBLE OPTIONS below.
 	Ensure at least <n> lines of surrounding context match before
 	and after each change.  When fewer lines of surrounding
 	context exist they all must match.  By default no context is
-	ever ignored.
+	ever ignored.  Implies --am.
 +
 See also INCOMPATIBLE OPTIONS below.
 

@@ -417,6 +424,7 @@ with `--keep-base` in order to drop those commits from your branch.
 --whitespace=<option>::
 	This flag is passed to the 'git apply' program
 	(see linkgit:git-apply[1]) that applies the patch.
+	Implies --am.
 +
 See also INCOMPATIBLE OPTIONS below.
 

@@ -567,6 +575,7 @@ INCOMPATIBLE OPTIONS
 
 The following options:
 
+ * --am
  * --whitespace
  * -C
 

index 1d510cd47b..8f8a22ba60 100644
@@ -430,9 +430,9 @@ __git_ps1 ()
 		__git_eread "$g/rebase-merge/msgnum" step
 		__git_eread "$g/rebase-merge/end" total
 		if [ -f "$g/rebase-merge/interactive" ]; then
-			r="|REBASE-i"
+			r="|REBASE"
 		else
-			r="|REBASE-m"
+			r="|REBASE"
 		fi
 	else
 		if [ -d "$g/rebase-apply" ]; then

index 88bc733ad6..7ca35d358d 100755
@@ -163,7 +163,7 @@ test_expect_success 'prompt - inside bare repository' '
 '
 
 test_expect_success 'prompt - interactive rebase' '
-	printf " (b1|REBASE-i 2/3)" >expected &&
+	printf " (b1|REBASE 2/3)" >expected &&
 	write_script fake_editor.sh <<-\EOF &&
 		echo "exec echo" >"$1"
 		echo "edit $(git log -1 --format="%h")" >>"$1"

@@ -180,7 +180,7 @@ test_expect_success 'prompt - interactive rebase' '
 '
 
 test_expect_success 'prompt - rebase merge' '
-	printf " (b2|REBASE-i 1/3)" >expected &&
+	printf " (b2|REBASE 1/3)" >expected &&
 	git checkout b2 &&
 	test_when_finished "git checkout master" &&
 	test_must_fail git rebase --merge b1 b2 &&

@@ -189,11 +189,11 @@ test_expect_success 'prompt - rebase merge' '
 	test_cmp expected "$actual"
 '
 
-test_expect_success 'prompt - rebase' '
+test_expect_success 'prompt - rebase am' '
 	printf " (b2|REBASE 1/3)" >expected &&
 	git checkout b2 &&
 	test_when_finished "git checkout master" &&
-	test_must_fail git rebase b1 b2 &&
+	test_must_fail git rebase --am b1 b2 &&
 	test_when_finished "git rebase --abort" &&
 	__git_ps1 >"$actual" &&
 	test_cmp expected "$actual"

index 1d0e2d27cc..ff32ca1080 100644
@@ -258,9 +258,25 @@ See also INCOMPATIBLE OPTIONS below.
 	original branch. The index and working tree are also left
 	unchanged as a result.
 
+--empty={drop,keep,ask}::
+	How to handle commits that become empty (because they contain a
+	subset of already upstream changes) or start empty.  With drop
+	(the default), commits that start or become empty are dropped.
+	With keep (implied by --exec), such commits are kept.  With ask
+	(implied by --interactive), the rebase will halt when an empty
+	commit is applied allowing you to choose whether to drop it or
+	commit it.  Also with ask, if the rebase is interactive then
+	commits which start empty will be commented out in the todo
+	action list (giving you a chance to uncomment).
++
+Note that this has no effect on commits which are already upstream (as
+can be checked via `git log --cherry-mark ...`), which are always
+dropped by rebase.
++
+See also INCOMPATIBLE OPTIONS below.
+
 --keep-empty::
-	Keep the commits that do not change anything from its
-	parents in the result.
+	Deprecated alias for what is now known as --empty=keep.
 +
 See also INCOMPATIBLE OPTIONS below.
 

@@ -569,6 +585,7 @@ are incompatible with the following options:
  * --interactive
  * --exec
  * --keep-empty
+ * --empty=
  * --edit-todo
  * --root when used in combination with --onto
 

@@ -580,6 +597,7 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --ignore-whitespace
  * --preserve-merges and --committer-date-is-author-date
  * --preserve-merges and --ignore-date
+ * --preserve-merges and --empty=
  * --keep-base and --onto
  * --keep-base and --root
 

@@ -588,19 +606,6 @@ BEHAVIORAL DIFFERENCES
 
 There are some subtle differences how the backends behave.
 
-Empty commits
-~~~~~~~~~~~~~
-
-The am backend drops any "empty" commits, regardless of whether the
-commit started empty (had no changes relative to its parent to
-start with) or ended empty (all changes were already applied
-upstream in other commits).
-
-The interactive backend drops commits by default that
-started empty and halts if it hits a commit that ended up empty.
-The `--keep-empty` option exists for the interactive backend to allow
-it to keep commits that started empty.
-
 Directory rename detection
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 

index 325072b0a3..d23e0bf778 100755
@@ -230,7 +230,7 @@ test_run_rebase () {
 test_run_rebase success ''
 test_run_rebase success -m
 test_run_rebase success -i
-test_have_prereq !REBASE_P || test_run_rebase failure -p
+test_have_prereq !REBASE_P || test_run_rebase success -p
 
 test_run_rebase () {
 	result=$1

@@ -245,7 +245,7 @@ test_run_rebase () {
 test_run_rebase success ''
 test_run_rebase success -m
 test_run_rebase success -i
-test_have_prereq !REBASE_P || test_run_rebase failure -p
+test_have_prereq !REBASE_P || test_run_rebase success -p
 test_run_rebase success --rebase-merges
 
 #       m

89 lines not on this page · raw message

index bec48e6a1f..468ebc1bef 100755
@@ -85,23 +85,27 @@ test_expect_failure REBASE_P 'Rebase -Xsubtree --keep-empty --preserve-merges --
 	verbose test "$(commit_message HEAD)" = "Empty commit"
 '
 
-test_expect_success 'Rebase -Xsubtree --keep-empty --onto commit' '
+test_expect_success 'Rebase -Xsubtree --empty=ask --onto commit' '
 	reset_rebase &&
 	git checkout -b rebase-onto to-rebase &&
-	test_must_fail git rebase -Xsubtree=files_subtree --keep-empty --onto files-master master &&
+	test_must_fail git rebase -Xsubtree=files_subtree --empty=ask --onto files-master master &&
 	: first pick results in no changes &&
-	git rebase --continue &&
+	test_must_fail git rebase --skip &&
+	: last pick was an empty commit that has no changes, but we want to keep it &&
+	git commit --allow-empty &&
 	verbose test "$(commit_message HEAD~2)" = "master4" &&
 	verbose test "$(commit_message HEAD~)" = "files_subtree/master5" &&
 	verbose test "$(commit_message HEAD)" = "Empty commit"
 '
 
-test_expect_success 'Rebase -Xsubtree --keep-empty --rebase-merges --onto commit' '
+test_expect_success 'Rebase -Xsubtree --empty=ask --rebase-merges --onto commit' '
 	reset_rebase &&
 	git checkout -b rebase-merges-onto to-rebase &&
-	test_must_fail git rebase -Xsubtree=files_subtree --keep-empty --rebase-merges --onto files-master --root &&
+	test_must_fail git rebase -Xsubtree=files_subtree --empty=ask --rebase-merges --onto files-master --root &&
 	: first pick results in no changes &&
-	git rebase --continue &&
+	test_must_fail git rebase --skip &&
+	: last pick was an empty commit that has no changes, but we want to keep it &&
+	git commit --allow-empty &&
 	verbose test "$(commit_message HEAD~2)" = "master4" &&
 	verbose test "$(commit_message HEAD~)" = "files_subtree/master5" &&
 	verbose test "$(commit_message HEAD)" = "Empty commit"

index b393e1e9fe..0c2c569f95 100755
@@ -18,11 +18,8 @@ test_expect_success 'setup' '
 '
 
 test_expect_success 'rebase -m' '
-	git rebase -m master >report &&
-	>expect &&
-	sed -n -e "/^Already applied: /p" \
-		-e "/^Committed: /p" report >actual &&
-	test_cmp expect actual
+	git rebase -m master >actual &&
+	test_must_be_empty actual
 '
 
 test_expect_success 'rebase against master twice' '

index 221b35f2df..79762b989a 100755
@@ -206,12 +206,18 @@ test_expect_success 'cherry-picked commits and fork-point work together' '
 	test_cmp expect D
 '
 
-test_expect_success 'rebase -q is quiet' '
+test_expect_success 'rebase --am -q is quiet' '
 	git checkout -b quiet topic &&
 	git rebase -q master >output.out 2>&1 &&
 	test_must_be_empty output.out
 '
 
+test_expect_success 'rebase --merge -q is quiet' '
+	git checkout -B quiet topic &&
+	git rebase --merge -q master >output.out 2>&1 &&
+	test_must_be_empty output.out
+'
+
 test_expect_success 'Rebase a commit that sprinkles CRs in' '
 	(
 		echo "One" &&

index 79762b989a..71fd6396cd 100755
@@ -165,11 +165,29 @@ test_expect_success 'rebase works with format.useAutoBase' '
 	git rebase master
 '
 
-test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg' '
+test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg (--merge)' '
 	git checkout -b default-base master &&
 	git checkout -b default topic &&
 	git config branch.default.remote . &&
 	git config branch.default.merge refs/heads/default-base &&
+	git rebase --merge &&
+	git rev-parse --verify default-base >expect &&
+	git rev-parse default~1 >actual &&
+	test_cmp expect actual &&
+	git checkout default-base &&
+	git reset --hard HEAD^ &&
+	git checkout default &&
+	git rebase --merge &&
+	git rev-parse --verify default-base >expect &&
+	git rev-parse default~1 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg' '
+	git checkout -B default-base master &&
+	git checkout -B default topic &&
+	git config branch.default.remote . &&
+	git config branch.default.merge refs/heads/default-base &&
 	git rebase &&
 	git rev-parse --verify default-base >expect &&
 	git rev-parse default~1 >actual &&

index 92f95b57da..7432c0e241 100755
@@ -44,19 +44,15 @@ test_rebase_same_head_ () {
 	test_expect_$status "git rebase$flag $* with $changes is $what with $cmp HEAD" "
 		oldhead=\$(git rev-parse HEAD) &&
 		test_when_finished 'git reset --hard \$oldhead' &&
+		cp .git/logs/HEAD expect &&
 		git rebase$flag $* >stdout &&
 		if test $what = work
 		then
-			# Must check this case first, for 'is up to
-			# date, rebase forced[...]rewinding head' cases
-			test_i18ngrep 'rewinding head' stdout
+			old=\$(wc -l <expect) &&
+			test_line_count '-gt' \$old .git/logs/HEAD
 		elif test $what = noop
 		then
-			test_i18ngrep 'is up to date' stdout &&
-			test_i18ngrep ! 'rebase forced' stdout
-		elif test $what = noop-force
-		then
-			test_i18ngrep 'is up to date, rebase forced' stdout
+			test_cmp expect .git/logs/HEAD
 		fi &&
 		newhead=\$(git rev-parse HEAD) &&
 		if test $cmp = same

@@ -71,14 +67,14 @@ test_rebase_same_head_ () {
 
 changes='no changes'
 test_rebase_same_head success noop same success work same
-test_rebase_same_head success noop same success noop-force same master
-test_rebase_same_head success noop same success noop-force diff --onto B B
-test_rebase_same_head success noop same success noop-force diff --onto B... B
-test_rebase_same_head success noop same success noop-force same --onto master... master
-test_rebase_same_head success noop same success noop-force same --keep-base master
-test_rebase_same_head success noop same success noop-force same --keep-base
-test_rebase_same_head success noop same success noop-force same --no-fork-point
-test_rebase_same_head success noop same success noop-force same --keep-base --no-fork-point
+test_rebase_same_head success noop same success work same master
+test_rebase_same_head success noop same success work diff --onto B B
+test_rebase_same_head success noop same success work diff --onto B... B
+test_rebase_same_head success noop same success work same --onto master... master
+test_rebase_same_head success noop same success work same --keep-base master
+test_rebase_same_head success noop same success work same --keep-base
+test_rebase_same_head success noop same success work same --no-fork-point
+test_rebase_same_head success noop same success work same --keep-base --no-fork-point
 test_rebase_same_head success noop same success work same --fork-point master
 test_rebase_same_head success noop same success work diff --fork-point --onto B B
 test_rebase_same_head success noop same success work diff --fork-point --onto B... B

@@ -91,14 +87,14 @@ test_expect_success 'add work same to side' '
 
 changes='our changes'
 test_rebase_same_head success noop same success work same
-test_rebase_same_head success noop same success noop-force same master
-test_rebase_same_head success noop same success noop-force diff --onto B B
-test_rebase_same_head success noop same success noop-force diff --onto B... B
-test_rebase_same_head success noop same success noop-force same --onto master... master
-test_rebase_same_head success noop same success noop-force same --keep-base master
-test_rebase_same_head success noop same success noop-force same --keep-base
-test_rebase_same_head success noop same success noop-force same --no-fork-point
-test_rebase_same_head success noop same success noop-force same --keep-base --no-fork-point
+test_rebase_same_head success noop same success work same master
+test_rebase_same_head success noop same success work diff --onto B B
+test_rebase_same_head success noop same success work diff --onto B... B
+test_rebase_same_head success noop same success work same --onto master... master
+test_rebase_same_head success noop same success work same --keep-base master
+test_rebase_same_head success noop same success work same --keep-base
+test_rebase_same_head success noop same success work same --no-fork-point
+test_rebase_same_head success noop same success work same --keep-base --no-fork-point
 test_rebase_same_head success noop same success work same --fork-point master
 test_rebase_same_head success noop same success work diff --fork-point --onto B B
 test_rebase_same_head success noop same success work diff --fork-point --onto B... B

@@ -112,8 +108,8 @@ test_expect_success 'add work same to upstream' '
 '
 
 changes='our and their changes'
-test_rebase_same_head success noop same success noop-force diff --onto B B
-test_rebase_same_head success noop same success noop-force diff --onto B... B
+test_rebase_same_head success noop same success work diff --onto B B
+test_rebase_same_head success noop same success work diff --onto B... B
 test_rebase_same_head success noop same success work diff --onto master... master
 test_rebase_same_head success noop same success work diff --keep-base master
 test_rebase_same_head success noop same success work diff --keep-base

index 7432c0e241..40388ccf9f 100755
@@ -30,6 +30,8 @@ test_rebase_same_head () {
 	shift &&
 	test_rebase_same_head_ $status_n $what_n $cmp_n "" "$*" &&
 	test_rebase_same_head_ $status_f $what_f $cmp_f " --no-ff" "$*"
+	test_rebase_same_head_ $status_n $what_n $cmp_n " --merge" "$*" &&
+	test_rebase_same_head_ $status_f $what_f $cmp_f " --merge --no-ff" "$*"
 }
 
 test_rebase_same_head_ () {

index ff32ca1080..f1ace07c38 100644
@@ -409,13 +409,10 @@ your branch contains commits which were dropped, this option can be used
 with `--keep-base` in order to drop those commits from your branch.
 
 --ignore-whitespace::
-	Behaves differently depending on which backend is selected.
-+
-'am' backend: When applying a patch, ignore changes in whitespace in
-context lines if necessary.
-+
-'interactive' backend: Treat lines with only whitespace changes as
-unchanged for the sake of a three-way merge.
+	Ignore whitespace-only changes in the commits being rebased,
+	which may avoid "unnecessary" conflicts.  (Both backends
+	currently have differing edgecase bugs with this option; see
+	BEHAVIORAL DIFFERENCES.)
 
 --whitespace=<option>::
 	This flag is passed to the 'git apply' program

@@ -609,9 +606,94 @@ There are some subtle differences how the backends behave.
 Directory rename detection
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Directory rename heuristics are enabled in the merge and interactive
-backends.  Due to the lack of accurate tree information, directory
-rename detection is disabled in the am backend.
+Due to the lack of accurate tree information (arising from
+constructing fake ancestors with the limited information available in
+patches), directory rename detection is disabled in the am backend.
+Disabled directory rename detection means that if one side of history
+renames a directory and the other adds new files to the old directory,
+then the new files will be left behind in the old directory without
+any warning at the time of rebasing that you may want to move these
+files into the new directory.
+
+Directory rename detection works with the merge and interactive
+backends to provide you warnings in such cases.
+
+Context
+~~~~~~~
+
+The am backend works by creating a sequence of patches (by calling
+`format-patch` internally), and then applying the patches in sequence
+(calling `am` internally).  Patches are composed of multiple hunks,
+each with line numbers, a context region, and the actual changes.  The
+line numbers have to be taken with some fuzz, since the other side
+will likely have inserted or deleted lines earlier in the file.  The
+context region is meant to help find how to adjust the line numbers in
+order to apply the changes to the right lines.  However, if multiple
+areas of the code have the same surrounding lines of context, the
+wrong one can be picked.  There are real-world cases where this has
+caused commits to be reapplied incorrectly with no conflicts reported.
+Setting diff.context to a larger value may prevent such types of
+problems, but increases the chance of spurious conflicts (since it
+will require more lines of matching context to apply).
+
+The interactive backend works with a full copy of each relevant file,
+insulating it from these types of problems.
+
+Labelling of conflicts markers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When there are content conflicts, the merge machinery tries to
+annotate each side's conflict markers with the commits where the
+content came from.  Since the am backend drops the original
+information about the rebased commits and their parents (and instead
+generates new fake commits based off limited information in the
+generated patches), those commits cannot be identified; instead it has
+to fall back to a commit summary.  Also, when merge.conflictStyle is
+set to diff3, the am backend will use "constructed merge base" to
+label the content from the merge base, and thus provide no information
+about the merge base commit whatsoever.
+
+The interactive backend works with the full commits on both sides of
+history and thus has no such limitations.
+
+--ignore-whitespace
+~~~~~~~~~~~~~~~~~~~
+
+The --ignore-whitespace option is supposed to ignore whitespace-only
+changes if it allows the code to merge cleanly.  Unfortunately, the
+different backends implement this differently, and both have different
+edge case bugs.
++
+'am' backend: When applying a patch, ignore changes in whitespace in
+context lines if necessary.  (Which implies that if the whitespace
+change was not in the context lines but on a line with a real change,
+then the rebase will still fail with "unnecessary" content conflicts.)
++
+'interactive' backend: Treat lines with only whitespace changes as
+unchanged for the sake of a three-way merge.  This means that if one
+side made no changes and the commits being rebased had whitespace-only
+changes, those whitespaces fixups will be discarded despite the fact
+that they present no content conflict.
+
+Miscellaneous differences
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are a few more behavioral differences that most folks would
+probably consider inconsequential but which are mentioned for
+completeness:
+
+* Reflog: The two backends will use different wording when describing
+  the changes made in the reflog, though both will make use of the
+  word "rebase".
+
+* Progress, informational, and error messages: The two backends
+  provide slightly different progress and informational messages.
+  Also, the am backend writes error messages (such as "Your files
+  would be overwritten...") to stdout, while the interactive backend
+  writes them to stderr.
+
+* State directories: The two backends keep their state in different
+  directories under .git/
 
 include::merge-strategies.txt[]