rebase [--onto O] A B: omit needless checkout
This teaches "git rebase [--onto O] A B" to omit an unnecessary checkout of branch B before it goes on. "git-rebase" originally was about rebasing the current branch to somewhere else, and when the extra parameter to name which branch to rebase was added, it defined the semantics to the safest but stupid "first switch to the named branch and then operate exactly the same way as if we were already on that branch". But the first thing the real part of "rebase" does is to reset the work tree and the index to the "onto" commit. Which means the "rebase that branch" form switched the work tree to the tip of the branch only to immediately switch again to another commit. This was wasteful. Signed-off-by: Junio C Hamano <gitster@pobox.com>
Junio C Hamano committed
Mar 15, 2008 at 13:17 UTC
0cb06644a569d92ea8b3b6e81bc8bd786d98920e
1 file changed
+32
-20
git-rebase.sh
+32
-20
@@ -309,22 +309,42 @@ then
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}
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fi
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-# If the branch to rebase is given, first switch to it.
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+# If the branch to rebase is given, that is the branch we will rebase
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+# $branch_name -- branch being rebased, or HEAD (already detached)
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+# $orig_head -- commit object name of tip of the branch before rebasing
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+# $head_name -- refs/heads/<that-branch> or "detached HEAD"
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+switch_to=
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case "$#" in
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2)
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+ # Is it "rebase other $branchname" or "rebase other $commit"?
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branch_name="$2"
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- git-checkout "$2" || usage
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+ switch_to="$2"
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+
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+ if git show-ref --verify --quiet -- "refs/heads/$2" &&
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+ branch=$(git rev-parse --verify "refs/heads/$2" 2>/dev/null)
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+ then
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+ head_name="refs/heads/$2"
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+ elif branch=$(git rev-parse --verify "$2" 2>/dev/null)
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+ then
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+ head_name="detached HEAD"
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+ else
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+ usage
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+ fi
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;;
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*)
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+ # Do not need to switch branches, we are already on it.
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if branch_name=`git symbolic-ref -q HEAD`
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then
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+ head_name=$branch_name
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branch_name=`expr "z$branch_name" : 'zrefs/heads/\(.*\)'`
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else
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+ head_name="detached HEAD"
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branch_name=HEAD ;# detached
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fi
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+ branch=$(git rev-parse --verify "${branch_name}^0") || exit
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;;
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esac
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-branch=$(git rev-parse --verify "${branch_name}^0") || exit
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+orig_head=$branch
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# Now we are rebasing commits $upstream..$branch on top of $onto
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@@ -335,6 +355,8 @@ if test "$upstream" = "$onto" && test "$mb" = "$onto" &&
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# linear history?
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! git rev-list --parents "$onto".."$branch" | grep " .* " > /dev/null
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then
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+ # Lazily switch to the target branch if needed...
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+ test -z "$switch_to" || git checkout "$switch_to"
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echo >&2 "Current branch $branch_name is up to date."
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exit 0
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fi
@@ -346,22 +368,11 @@ then
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GIT_PAGER='' git diff --stat --summary "$mb" "$onto"
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fi
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-# move to a detached HEAD
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-orig_head=$(git rev-parse HEAD^0)
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-head_name=$(git symbolic-ref HEAD 2> /dev/null)
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-case "$head_name" in
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-'')
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- head_name="detached HEAD"
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- ;;
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-*)
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- git checkout "$orig_head" > /dev/null 2>&1 ||
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- die "could not detach HEAD"
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- ;;
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-esac
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-
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-# Rewind the head to "$onto"; this saves our current head in ORIG_HEAD.
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+# Detach HEAD and reset the tree
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echo "First, rewinding head to replay your work on top of it..."
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-git-reset --hard "$onto"
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+git checkout "$onto^0" >/dev/null 2>&1 ||
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+ die "could not detach HEAD"
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+# git reset --hard "$onto^0"
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# If the $onto is a proper descendant of the tip of the branch, then
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# we just fast forwarded.
@@ -374,7 +385,8 @@ fi
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if test -z "$do_merge"
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then
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- git format-patch -k --stdout --full-index --ignore-if-in-upstream "$upstream"..ORIG_HEAD |
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+ git format-patch -k --stdout --full-index --ignore-if-in-upstream \
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+ "$upstream..$orig_head" |
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git am $git_am_opt --rebasing --resolvemsg="$RESOLVEMSG" &&
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move_to_original_branch
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ret=$?
@@ -397,7 +409,7 @@ echo "$orig_head" > "$dotest/orig-head"
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echo "$head_name" > "$dotest/head-name"
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msgnum=0
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-for cmt in `git rev-list --reverse --no-merges "$upstream"..ORIG_HEAD`
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+for cmt in `git rev-list --reverse --no-merges "$upstream..$orig_head"`
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do
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msgnum=$(($msgnum + 1))
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echo "$cmt" > "$dotest/cmt.$msgnum"