filter-branch: provide the convenience functions also for commit filters

Move the convenience functions to the top of git-filter-branch.sh, and
return from the script when the environment variable SOURCE_FUNCTIONS is
set.

By sourcing git-filter-branch with that variable set automatically, all
commit filters may access the convenience functions like "map".

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-filter-branch.txt

@@ -112,9 +112,6 @@ OPTIONS
 As a special extension, the commit filter may emit multiple
 commit ids; in that case, ancestors of the original commit will
 have all of them as parents.
-+
-Note that the 'map' function is not available in the commit filter yet.
-This will be changed in a future version.
 
 --tag-name-filter <command>::
 	This is the filter for rewriting tag names. When passed,

git-filter-branch.sh

@@ -8,15 +8,6 @@
 # a new branch. You can specify a number of filters to modify the commits,
 # files and trees.
 
-USAGE="[--env-filter <command>] [--tree-filter <command>] \
-[--index-filter <command>] [--parent-filter <command>] \
-[--msg-filter <command>] [--commit-filter <command>] \
-[--tag-name-filter <command>] [--subdirectory-filter <directory>] \
-[--original <namespace>] [-d <directory>] [-f | --force] \
-[<rev-list options>...]"
-
-. git-sh-setup
-
 warn () {
         echo "$*" >&2
 }
@@ -75,6 +66,20 @@ set_ident () {
 	echo "[ -n \"\$GIT_${uid}_NAME\" ] || export GIT_${uid}_NAME=\"\${GIT_${uid}_EMAIL%%@*}\""
 }
 
+# This script can be sourced by the commit filter to get the functions
+test "a$SOURCE_FUNCTIONS" = a1 && return
+this_script="$(cd "$(dirname "$0")"; pwd)"/$(basename "$0")
+export this_script
+
+USAGE="[--env-filter <command>] [--tree-filter <command>] \
+[--index-filter <command>] [--parent-filter <command>] \
+[--msg-filter <command>] [--commit-filter <command>] \
+[--tag-name-filter <command>] [--subdirectory-filter <directory>] \
+[--original <namespace>] [-d <directory>] [-f | --force] \
+[<rev-list options>...]"
+
+. git-sh-setup
+
 tempdir=.git-rewrite
 filter_env=
 filter_tree=
@@ -131,7 +136,7 @@ do
 		filter_msg="$OPTARG"
 		;;
 	--commit-filter)
-		filter_commit="$OPTARG"
+		filter_commit='SOURCE_FUNCTIONS=1 . "$this_script";'" $OPTARG"
 		;;
 	--tag-name-filter)
 		filter_tag_name="$OPTARG"

t/t7003-filter-branch.sh

@@ -159,4 +159,14 @@ test_expect_success 'barf on invalid name' '
 	! git filter-branch -f HEAD^
 '
 
+test_expect_success '"map" works in commit filter' '
+	git filter-branch -f --commit-filter "\
+		parent=\$(git rev-parse \$GIT_COMMIT^) &&
+		mapped=\$(map \$parent) &&
+		actual=\$(echo \"\$@\" | sed \"s/^.*-p //\") &&
+		test \$mapped = \$actual &&
+		git commit-tree \"\$@\";" master~2..master &&
+	git rev-parse --verify master
+'
+
 test_done