doc-diff: add --clean mode to remove temporary working gunk

As part of its operation, doc-diff creates a bunch of temporary
working files and holds onto them in order to speed up subsequent
invocations. These files are never deleted. Moreover, it creates a
temporary working tree (via git-wortkree) which likewise never gets
removed.

Without knowing the implementation details of the tool, a user may not
know how to clean up manually afterward. Worse, the user may find it
surprising and alarming to discover a working tree which s/he did not
create explicitly.

To address these issues, add a --clean mode which removes the
temporary working tree and deletes all generated files.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/doc-diff

@@ -10,20 +10,25 @@
 
 OPTIONS_SPEC="\
 doc-diff [options] <from> <to> [-- <diff-options>]
+doc-diff (-c|--clean)
 --
 j=n	parallel argument to pass to make
 f	force rebuild; do not rely on cached results
+c,clean	cleanup temporary working files
 "
 SUBDIRECTORY_OK=1
 . "$(git --exec-path)/git-sh-setup"
 
 parallel=
 force=
+clean=
 while test $# -gt 0
 do
 	case "$1" in
 	-j)
 		parallel=$2; shift ;;
+	-c|--clean)
+		clean=t ;;
 	-f)
 		force=t ;;
 	--)
@@ -34,6 +39,17 @@ do
 	shift
 done
 
+cd_to_toplevel
+tmp=Documentation/tmp-doc-diff
+
+if test -n "$clean"
+then
+	test $# -eq 0 || usage
+	git worktree remove --force "$tmp/worktree" 2>/dev/null
+	rm -rf "$tmp"
+	exit 0
+fi
+
 if test -z "$parallel"
 then
 	parallel=$(getconf _NPROCESSORS_ONLN 2>/dev/null)
@@ -50,9 +66,6 @@ to=$1; shift
 from_oid=$(git rev-parse --verify "$from") || exit 1
 to_oid=$(git rev-parse --verify "$to") || exit 1
 
-cd_to_toplevel
-tmp=Documentation/tmp-doc-diff
-
 if test -n "$force"
 then
 	rm -rf "$tmp"