rebase: use reflog to find common base with upstream

Commit 15a147e (rebase: use @{upstream} if no upstream specified,
2011-02-09) says:

	Make it default to 'git rebase @{upstream}'. That is also what
	'git pull [--rebase]' defaults to, so it only makes sense that
	'git rebase' defaults to the same thing.

but that isn't actually the case.  Since commit d44e712 (pull: support
rebased upstream + fetch + pull --rebase, 2009-07-19), pull has actually
chosen the most recent reflog entry which is an ancestor of the current
branch if it can find one.

Add a '--fork-point' argument to git-rebase that can be used to trigger
this behaviour.  This option is turned on by default if no non-option
arguments are specified on the command line, otherwise we treat an
upstream specified on the command-line literally.

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 94e07fdab550dcac70734fb79724b00cf8d23edc..2889be6bdc4a1a243585e43def2e7416a9aa7038 100644 (file)
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -324,6 +324,16 @@ fresh commits so it can be remerged successfully without needing to "revert
 the reversion" (see the
 link:howto/revert-a-faulty-merge.html[revert-a-faulty-merge How-To] for details).
 
+--fork-point::
+--no-fork-point::
+       Use 'git merge-base --fork-point' to find a better common ancestor
+       between `upstream` and `branch` when calculating which commits have
+       have been introduced by `branch` (see linkgit:git-merge-base[1]).
++
+If no non-option arguments are given on the command line, then the default is
+`--fork-point @{u}` otherwise the `upstream` argument is interpreted literally
+unless the `--fork-point` option is specified.
+
 --ignore-whitespace::
 --whitespace=<option>::
        These flag are passed to the 'git apply' program

diff --git a/git-rebase.sh b/git-rebase.sh
index 226752fbff62f4f27da95f7d711c898503fd7148..7185dc84387d6e20299fdda86800372445b9318e 100755 (executable)
--- a/git-rebase.sh
+++ b/git-rebase.sh
@@ -14,6 +14,7 @@ git-rebase --continue | --abort | --skip | --edit-todo
 v,verbose!         display a diffstat of what changed upstream
 q,quiet!           be quiet. implies --no-stat
 autostash!         automatically stash/stash pop before and after
+fork-point         use 'merge-base --fork-point' to refine upstream
 onto=!             rebase onto given branch instead of upstream
 p,preserve-merges! try to recreate merges instead of ignoring them
 s,strategy=!       use the given merge strategy
@@ -66,6 +67,7 @@ verbose=
 diffstat=
 test "$(git config --bool rebase.stat)" = true && diffstat=t
 autostash="$(git config --bool rebase.autostash || echo false)"
+fork_point=auto
 git_am_opt=
 rebase_root=
 force_rebase=
@@ -260,6 +262,12 @@ do
        --no-autosquash)
                autosquash=
                ;;
+       --fork-point)
+               fork_point=t
+               ;;
+       --no-fork-point)
+               fork_point=
+               ;;
        -M|-m)
                do_merge=t
                ;;
@@ -437,6 +445,8 @@ then
                        error_on_missing_default_upstream "rebase" "rebase" \
                                "against" "git rebase <branch>"
                fi
+
+               test "$fork_point" = auto && fork_point=t
                ;;
        *)      upstream_name="$1"
                shift
@@ -522,6 +532,15 @@ case "$#" in
        ;;
 esac
 
+if test "$fork_point" = t
+then
+       new_upstream=$(git merge-base --fork-point "$upstream_name" "$switch_to")
+       if test -n "$new_upstream"
+       then
+               upstream=$new_upstream
+       fi
+fi
+
 if test "$autostash" = true && ! (require_clean_work_tree) 2>/dev/null
 then
        stash_sha1=$(git stash create "autostash") ||

diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index ebf93b0695dfac37fc276e1f07377d858eb3e1da..998503db12eb115e8e160937d456dfd9cb46311f 100755 (executable)
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -134,12 +134,14 @@ test_expect_success 'fail when upstream arg is missing and not configured' '
        test_must_fail git rebase
 '
 
-test_expect_success 'default to @{upstream} when upstream arg is missing' '
+test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg' '
        git checkout -b default topic &&
        git config branch.default.remote . &&
        git config branch.default.merge refs/heads/master &&
        git rebase &&
-       test "$(git rev-parse default~1)" = "$(git rev-parse master)"
+       git rev-parse --verify master >expect &&
+       git rev-parse default~1 >actual &&
+       test_cmp expect actual
 '
 
 test_expect_success 'rebase -q is quiet' '