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>

scripts/libmakepkg/source.sh.in

@@ -59,26 +59,11 @@ download_sources() {
 		pushd "$SRCDEST" &>/dev/null
 
 		local proto=$(get_protocol "$netfile")
-		case "$proto" in
-			local)
-				download_local "$netfile"
-				;;
-			bzr)
-				(( get_vcs )) && download_bzr "$netfile"
-				;;
-			git)
-				(( get_vcs )) && download_git "$netfile"
-				;;
-			hg)
-				(( get_vcs )) && download_hg "$netfile"
-				;;
-			svn)
-				(( get_vcs )) && download_svn "$netfile"
-				;;
-			*)
-				download_file "$netfile"
-				;;
-		esac
+		if declare -f download_$proto > /dev/null; then
+			download_$proto "$netfile"
+		else
+			download_file "$netfile"
+		fi
 
 		popd &>/dev/null
 	done
@@ -92,22 +77,10 @@ extract_sources() {
 	for netfile in "${all_sources[@]}"; do
 		local file=$(get_filename "$netfile")
 		local proto=$(get_protocol "$netfile")
-		case "$proto" in
-			bzr)
-				extract_bzr "$netfile"
-				;;
-			git)
-				extract_git "$netfile"
-				;;
-			hg)
-				extract_hg "$netfile"
-				;;
-			svn)
-				extract_svn "$netfile"
-				;;
-			*)
-				extract_file "$file"
-				;;
-		esac
+		if declare -f extract_$proto > /dev/null; then
+			extract_$proto "$netfile"
+		else
+			extract_file "$file"
+		fi
 	done
 }

scripts/libmakepkg/source/bzr.sh.in

@@ -29,6 +29,11 @@ source "$LIBRARY/util/pkgbuild.sh"
 
 
 download_bzr() {
+	# 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 url=$(get_url "$netfile")

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")

scripts/libmakepkg/source/hg.sh.in

@@ -29,6 +29,11 @@ source "$LIBRARY/util/pkgbuild.sh"
 
 
 download_hg() {
+	# 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")

scripts/libmakepkg/source/svn.sh.in

@@ -29,6 +29,11 @@ source "$LIBRARY/util/pkgbuild.sh"
 
 
 download_svn() {
+	# 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 fragment=${netfile#*#}