makepkg: ensure vcs download tool are installed when required

Add an array VCSCLIENTS to makepkg.conf that matches vcs source protocols
to the package containing the software needed for handling the source.

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

doc/makepkg.conf.5.txt

@@ -47,6 +47,11 @@ Options
 	be replaced with the local file name, plus a ``.part'' extension, which allows
 	makepkg to handle resuming file downloads.
 
+**VCSCLIENTS=(**\'protocol::package' ...**)**::
+	Sets the packages required to fetch version controlled source files. When
+	required, makepkg will check that these packages are installed or are included
+	in the `depends` or `makedepends` arrays in the PKGBUILD.
+
 **CARCH=**"carch"::
 	Specifies your computer architecture; possible values include such things
 	as ``i686'', ``x86_64'', ``ppc'', etc. This should be automatically set on

scripts/makepkg.sh.in

@@ -2402,6 +2402,71 @@ check_pkgver() {
 	return $ret
 }
 
+get_vcsclient() {
+	local proto=${1%%+*}
+
+	local i
+	for i in "${VCSCLIENTS[@]}"; do
+		local handler="${i%%::*}"
+		if [[ $proto = "$handler" ]]; then
+			local client="${i##*::}"
+			break
+		fi
+	done
+
+	# if we didn't find an client, return an error
+	if [[ -z $client ]]; then
+		error "$(gettext "Unknown download protocol: %s")" "$proto"
+		plain "$(gettext "Aborting...")"
+		exit 1 # $E_CONFIG_ERROR
+	fi
+
+	printf "%s\n" "$client"
+}
+
+check_vcs_software() {
+	local ret=0
+
+	if (( SOURCEONLY == 1 )); then
+		# we will not download VCS sources
+		return $ret
+	fi
+
+	if [[ -z $PACMAN_PATH ]]; then
+		warning "$(gettext "Cannot find the %s binary needed to check VCS source requirements.")" "$PACMAN"
+		return $ret
+	fi
+
+	for netfile in ${source[@]}; do
+		local proto=$(get_protocol "$netfile")
+
+		case $proto in
+			bzr*|git*|hg*|svn*)
+				if ! type -p ${proto%%+*} > /dev/null; then
+					local client
+					client=$(get_vcsclient "$proto") || exit $?
+					# ensure specified program is installed
+					local uninstalled
+					uninstalled="$(set +E; check_deps $client)" || exit 1
+					# if not installed, check presence in depends or makedepends
+					if [[ -n "$uninstalled" ]] && (( ! NODEPS )); then
+						if ! in_array "$client" ${depends[@]} ${makedepends[@]}; then
+							error "$(gettext "Cannot find the %s package needed to handle %s sources.")" \
+									"$client" "${proto%%+*}"
+							ret=1
+						fi
+					fi
+				fi
+				;;
+			*)
+				# non VCS source
+				;;
+		esac
+	done
+
+	return $ret
+}
+
 check_software() {
 	# check for needed software
 	local ret=0
@@ -2493,6 +2558,11 @@ check_software() {
 		fi
 	fi
 
+	# tools to download vcs sources
+	if ! check_vcs_software; then
+		ret=1
+	fi
+
 	return $ret
 }