doc-diff: support diffing from/to AsciiDoc(tor)

Provide `--from-asciidoctor` and `--to-asciidoctor` to select that the
"from" resp. "to" commit should be built with Asciidoctor, and provide
an `--asciidoctor` shortcut for giving both. Similarly, provide
--{from-,to-,}asciidoc for explicitly selecting AsciiDoc.

Implement this using the USE_ASCIIDOCTOR flag. Let's not enforce a
default here, but instead just let the Makefile fall back on whatever is
in config.mak, so that `./doc-diff foo bar` without any of of these new
options behaves exactly like it did before this commit.

Encode the choice into the directory names of our "installed" and
"rendered" files, so that we can run `./doc-diff --from-asciidoc
--to-asciidoctor HEAD HEAD` without our two runs stomping on each other.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/doc-diff

@@ -12,9 +12,15 @@ 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
+j=n			parallel argument to pass to make
+f			force rebuild; do not rely on cached results
+c,clean			cleanup temporary working files
+from-asciidoc		use asciidoc with the 'from'-commit
+from-asciidoctor	use asciidoctor with the 'from'-commit
+asciidoc		use asciidoc with both commits
+to-asciidoc		use asciidoc with the 'to'-commit
+to-asciidoctor		use asciidoctor with the 'to'-commit
+asciidoctor		use asciidoctor with both commits
 "
 SUBDIRECTORY_OK=1
 . "$(git --exec-path)/git-sh-setup"
@@ -22,6 +28,8 @@ SUBDIRECTORY_OK=1
 parallel=
 force=
 clean=
+from_program=
+to_program=
 while test $# -gt 0
 do
 	case "$1" in
@@ -31,6 +39,20 @@ do
 		clean=t ;;
 	-f)
 		force=t ;;
+	--from-asciidoctor)
+		from_program=-asciidoctor ;;
+	--to-asciidoctor)
+		to_program=-asciidoctor ;;
+	--asciidoctor)
+		from_program=-asciidoctor
+		to_program=-asciidoctor ;;
+	--from-asciidoc)
+		from_program=-asciidoc ;;
+	--to-asciidoc)
+		to_program=-asciidoc ;;
+	--asciidoc)
+		from_program=-asciidoc
+		to_program=-asciidoc ;;
 	--)
 		shift; break ;;
 	*)
@@ -79,8 +101,21 @@ then
 	ln -s "$dots/config.mak" "$tmp/worktree/config.mak"
 fi
 
-from_dir=$from_oid &&
-to_dir=$to_oid &&
+construct_makemanflags () {
+	if test "$1" = "-asciidoc"
+	then
+		echo USE_ASCIIDOCTOR=
+	elif test "$1" = "-asciidoctor"
+	then
+		echo USE_ASCIIDOCTOR=YesPlease
+	fi
+}
+
+from_makemanflags=$(construct_makemanflags "$from_program") &&
+to_makemanflags=$(construct_makemanflags "$to_program") &&
+
+from_dir=$from_oid$from_program &&
+to_dir=$to_oid$to_program &&
 
 # generate_render_makefile <srcdir> <dstdir>
 generate_render_makefile () {
@@ -97,7 +132,7 @@ generate_render_makefile () {
 	done
 }
 
-# render_tree <committish_oid> <directory_name>
+# render_tree <committish_oid> <directory_name> <makemanflags>
 render_tree () {
 	# Skip install-man entirely if we already have an installed directory.
 	# We can't rely on make here, since "install-man" unconditionally
@@ -107,10 +142,12 @@ render_tree () {
 	# through.
 	oid=$1 &&
 	dname=$2 &&
+	makemanflags=$3 &&
 	if ! test -d "$tmp/installed/$dname"
 	then
 		git -C "$tmp/worktree" checkout --detach "$oid" &&
 		make -j$parallel -C "$tmp/worktree" \
+			$makemanflags \
 			GIT_VERSION=omitted \
 			SOURCE_DATE_EPOCH=0 \
 			DESTDIR="$tmp/installed/$dname+" \
@@ -130,6 +167,6 @@ render_tree () {
 	fi
 }
 
-render_tree $from_oid $from_dir &&
-render_tree $to_oid $to_dir &&
+render_tree $from_oid $from_dir $from_makemanflags &&
+render_tree $to_oid $to_dir $to_makemanflags &&
 git -C $tmp/rendered diff --no-index "$@" $from_dir $to_dir