makepkg: add basic support for alternatives

Alternatives are specified in makepkg via (e.g.):

alternative=('sh')

There should be a file (e.g.) sh.alternative alongside the PKGBUILD containing
a list of symlinks to be created with the alternative is active.  This file is
stored in the root of the package as (e.g.) .ALTERNATIVE.sh.

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

doc/PKGBUILD.5.asciidoc

@@ -402,8 +402,8 @@ All options and directives for the split packages default to the global values
 given in the PKGBUILD. Nevertheless, the following ones can be overridden within
 each split package's packaging function:
 `pkgdesc`, `arch`, `url`, `license`, `groups`, `depends`, `optdepends`,
-`provides`, `conflicts`, `replaces`, `backup`, `options`, `install`, and
-`changelog`.
+`provides`, `conflicts`, `replaces`, `backup`, `options`, `install`,
+`changelog` and `alternative`.
 
 Note that makepkg does not consider split package `depends` when checking
 if dependencies are installed before package building and with `--syncdeps`.

scripts/libmakepkg/lint_pkgbuild/alternative.sh.in

@@ -0,0 +1,41 @@
+#!/bin/bash
+#
+#   alternative.sh - Check the files associated with the 'alternative'
+#   array exist.
+#
+#   Copyright (c) 2020 Pacman Development Team <pacman-dev@archlinux.org>
+#
+#   This program is free software; you can redistribute it and/or modify
+#   it under the terms of the GNU General Public License as published by
+#   the Free Software Foundation; either version 2 of the License, or
+#   (at your option) any later version.
+#
+#   This program is distributed in the hope that it will be useful,
+#   but WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#   GNU General Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License
+#   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+[[ -n "$LIBMAKEPKG_LINT_PKGBUILD_ALTERNATIVE_SH" ]] && return
+LIBMAKEPKG_LINT_PKGBUILD_ALTERNATIVE_SH=1
+
+LIBRARY=${LIBRARY:-'@libmakepkgdir@'}
+
+source "$LIBRARY/util/message.sh"
+source "$LIBRARY/util/pkgbuild.sh"
+source "$LIBRARY/lint_pkgbuild/util.sh"
+
+
+lint_pkgbuild_functions+=('lint_alternative')
+
+
+lint_alternative() {
+	local ret=0
+
+	check_files_exist 'alternative' "${alternative[@]/%/.alternative}" || ret=1
+
+	return $ret
+}

scripts/libmakepkg/lint_pkgbuild/meson.build

@@ -1,6 +1,7 @@
 libmakepkg_module = 'lint_pkgbuild'
 
 sources = [
+  'alternative.sh.in',
   'arch.sh.in',
   'arch_specific.sh.in',
   'backup.sh.in',

scripts/libmakepkg/util/schema.sh.in

@@ -28,8 +28,8 @@ source "$LIBRARY/util/util.sh"
 
 known_hash_algos=({ck,md5,sha{1,224,256,384,512},b2})
 
-pkgbuild_schema_arrays=(arch backup checkdepends conflicts depends groups
-                        license makedepends noextract optdepends options
+pkgbuild_schema_arrays=(alternative arch backup checkdepends conflicts depends
+                        groups license makedepends noextract optdepends options
                         provides replaces source validpgpkeys
                         "${known_hash_algos[@]/%/sums}")
 
@@ -42,7 +42,7 @@ pkgbuild_schema_arch_arrays=(checkdepends conflicts depends makedepends
 
 pkgbuild_schema_package_overrides=(pkgdesc arch url license groups depends
                                    optdepends provides conflicts replaces
-                                   backup options install changelog)
+                                   backup options install changelog alternative)
 
 readonly -a known_hash_algos pkgbuild_schema_arrays \
 	pkgbuild_schema_strings pkgbuild_schema_arch_arrays \

scripts/makepkg.sh.in

@@ -710,6 +710,16 @@ create_package() {
 		fi
 	done
 
+	# check for alternative files
+	for i in ${alternative[@]}; do
+		msg2 "$(gettext "Adding %s file...")" "$i.alternative"
+		if ! cp "$startdir/$i.alternative" ".ALTERNATIVE.$i"; then
+			error "$(gettext "Failed to add %s file to package.")" "$i.alternative"
+			exit $E_MISSING_FILE
+		fi
+		chmod 644 ".ALTERNATIVE.$i"
+	done
+
 	# tar it up
 	local fullver=$(get_full_version)
 	local pkg_file="$PKGDEST/${pkgname}-${fullver}-${pkgarch}${PKGEXT}"