libmakepkg: implement extendable source protocols

Lookup the existence of matching functions for each protocol, and
fallback on the generic file handler. New source protocols can then be
added via thirdparty libmakepkg drop-ins without requiring modifications
to source.sh

Fixes FS#49076

Signed-off-by: Allan McRae <allan@archlinux.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/scripts/libmakepkg/source/git.sh.in b/scripts/libmakepkg/source/git.sh.in
index 130c11e1..497a668c 100644
--- a/scripts/libmakepkg/source/git.sh.in
+++ b/scripts/libmakepkg/source/git.sh.in
@@ -29,6 +29,11 @@ source "$LIBRARY/util/pkgbuild.sh"
 
 
 download_git() {
+	# abort early if parent says not to fetch
+	if declare -p get_vcs > /dev/null 2>&1; then
+		(( get_vcs )) || return
+	fi
+
 	local netfile=$1
 
 	local dir=$(get_filepath "$netfile")