rebase: allow rebasing onto different base.

Junio C Hamano · Junio C Hamano · commit e646c9c8c0aa · 2006-02-14T16:10:49.000-08:00
This allows you to rewrite history a bit more flexibly, by
separating the other branch name and new branch point.  By
default, the new branch point is the same as the tip of the
other branch as before, but you can specify where you graft the
rebased branch onto.

When you have this ancestry graph:

          A---B---C topic
         /
    D---E---F---G master

	$ git rebase --onto master~1 master topic

would rewrite the history to look like this:

	      A'\''--B'\''--C'\'' topic
	     /
    D---E---F---G master

Signed-off-by: Junio C Hamano &lt;junkio@cox.net&gt;
diff --git a/git-rebase.sh b/git-rebase.sh
@@ -3,10 +3,48 @@
 # Copyright (c) 2005 Junio C Hamano.
 #
 
-USAGE='<upstream> [<head>]'
+USAGE='[--onto <newbase>] <upstream> [<branch>]'
+LONG_USAGE='If <branch> is specified, switch to that branch first.  Then,
+extract commits in the current branch that are not in <upstream>,
+and reconstruct the current on top of <upstream>, discarding the original
+development history.  If --onto <newbase> is specified, the history is
+reconstructed on top of <newbase>, instead of <upstream>.  For example,
+while on "topic" branch:
+
+          A---B---C topic
+         /
+    D---E---F---G master
+
+	$ '"$0"' --onto master~1 master topic
+
+would rewrite the history to look like this:
+
+
+	      A'\''--B'\''--C'\'' topic
+	     /
+    D---E---F---G master
+'
+
 . git-sh-setup
 
-case $# in 1|2) ;; *) usage ;; esac
+unset newbase
+while case "$#" in 0) break ;; esac
+do
+	case "$1" in
+	--onto)
+		test 2 -le "$#" || usage
+		newbase="$2"
+		shift
+		;;
+	-*)
+		usage
+		;;
+	*)
+		break
+		;;
+	esac
+	shift
+done
 
 # Make sure we do not have .dotest
 if mkdir .dotest
@@ -30,37 +68,52 @@ case "$diff" in
 	;;
 esac
 
-# The other head is given.  Make sure it is valid.
-other=$(git-rev-parse --verify "$1^0") || usage
-
-# Make sure the branch to rebase is valid.
-head=$(git-rev-parse --verify "${2-HEAD}^0") || exit
+# The upstream head must be given.  Make sure it is valid.
+upstream_name="$1"
+upstream=`git rev-parse --verify "${upstream_name}^0"` ||
+    die "invalid upsteram $upstream_name"
 
 # If the branch to rebase is given, first switch to it.
 case "$#" in
 2)
+	branch_name="$2"
 	git-checkout "$2" || usage
+	;;
+*)
+	branch_name=`git symbolic-ref HEAD` || die "No current branch"
+	branch_name=`expr "$branch_name" : 'refs/heads/\(.*\)'`
+	;;
 esac
+branch=$(git-rev-parse --verify "${branch_name}^0") || exit
 
-mb=$(git-merge-base "$other" "$head")
+# Make sure the branch to rebase onto is valid.
+onto_name=${newbase-"$upstream_name"}
+onto=$(git-rev-parse --verify "${onto_name}^0") || exit
 
-# Check if we are already based on $other.
-if test "$mb" = "$other"
+# Now we are rebasing commits $upstream..$branch on top of $onto
+
+# Check if we are already based on $onto, but this should be
+# done only when upstream and onto are the same.
+if test "$upstream" = "onto"
 then
-	echo >&2 "Current branch `git-symbolic-ref HEAD` is up to date."
-	exit 0
+	mb=$(git-merge-base "$onto" "$branch")
+	if test "$mb" = "$onto"
+	then
+		echo >&2 "Current branch $branch_name is up to date."
+		exit 0
+	fi
 fi
 
-# Rewind the head to "$other"
-git-reset --hard "$other"
+# Rewind the head to "$onto"; this saves our current head in ORIG_HEAD.
+git-reset --hard "$onto"
 
-# If the $other is a proper descendant of the tip of the branch, then
+# If the $onto is a proper descendant of the tip of the branch, then
 # we just fast forwarded.
-if test "$mb" = "$head"
+if test "$mb" = "$onto"
 then
-	echo >&2 "Fast-forwarded $head to $other."
+	echo >&2 "Fast-forwarded $branch to $newbase."
 	exit 0
 fi
 
-git-format-patch -k --stdout --full-index "$other" ORIG_HEAD |
+git-format-patch -k --stdout --full-index "$upstream" ORIG_HEAD |
 git am --binary -3 -k
