xbps-src: support "alternatives" from xbps-0.48.

Manual.md

@@ -493,6 +493,10 @@ pkgver the resulting package should revert. This field *must* be defined before
 defined in `reverts` must be lesser than the one defined in `version`.
 example: `reverts="2.0_1 2.0_2"`
 
+- `alternatives` A white space separated list of supported alternatives the package provides.
+A list is composed of three components separated by a colon: group, symlink and target.
+i.e `alternatives="vi:/usr/bin/vi:/usr/bin/nvi ex:/usr/bin/ex:/usr/bin/nvi-ex"`.
+
 <a id="repositories"></a>
 #### Repositories
 

common/environment/setup-subpkg/subpkg.sh

@@ -2,7 +2,7 @@
 # a package template and can also be used in subpkgs.
 
 ## VARIABLES
-unset -v noarch conf_files mutable_files preserve triggers
+unset -v noarch conf_files mutable_files preserve triggers alternatives
 unset -v depends run_depends replaces provides conflicts tags
 
 # hooks/post-install/03-strip-and-debug-pkgs

common/hooks/do-pkg/00-gen-pkg.sh

@@ -82,6 +82,12 @@ genpkg() {
 			_conf_files="${_conf_files} ${f}"
 		done
 	fi
+	if [ -n "$alternatives" ]; then
+		local _alternatives=
+		for f in ${alternatives}; do
+			_alternatives="${_alternatives} ${f}"
+		done
+	fi
 
 	msg_normal "Creating $binpkg for repository $pkgdir ...\n"
 
@@ -100,6 +106,7 @@ genpkg() {
 		${_gitrevs:+--source-revisions "${_gitrevs}"} \
 		${_shprovides:+--shlib-provides "${_shprovides}"} \
 		${_shrequires:+--shlib-requires "${_shrequires}"} \
+		${_alternatives:+--alternatives "${_alternatives}"} \
 		${_preserve:+--preserve} \
 		${_tags:+--tags "${tags}"} \
 		--architecture ${arch} \