app-alternatives/awk: Sync with Gentoo

It's from Gentoo commit d4c96a45f9e0c5401a6d4df4867dc85348fd7989.

sdk_container/src/third_party/portage-stable/app-alternatives/awk/awk-3.ebuild

@@ -3,53 +3,68 @@
 
 EAPI=8
 
-DESCRIPTION="/bin/awk and /usr/bin/awk symlinks"
-HOMEPAGE="https://wiki.gentoo.org/wiki/Project:Base/Alternatives"
-SRC_URI=""
-S=${WORKDIR}
+ALTERNATIVES=(
+	gawk:sys-apps/gawk
+	busybox:sys-apps/busybox
+	mawk:sys-apps/mawk
+	nawk:sys-apps/nawk
+)
 
-LICENSE="CC0-1.0"
-SLOT="0"
+inherit app-alternatives
+
+DESCRIPTION="/bin/awk and /usr/bin/awk symlinks"
 KEYWORDS="~alpha ~amd64 ~arm ~arm64 ~hppa ~ia64 ~loong ~m68k ~mips ~ppc ~ppc64 ~riscv ~s390 ~sparc ~x86 ~x64-cygwin ~amd64-linux ~x86-linux ~ppc-macos ~x64-macos ~sparc-solaris ~sparc64-solaris ~x64-solaris ~x86-solaris"
-IUSE="busybox +gawk mawk nawk split-usr"
-REQUIRED_USE="^^ ( busybox gawk mawk nawk )"
+IUSE="split-usr"
 
 RDEPEND="
-	busybox? ( sys-apps/busybox )
-	gawk? ( sys-apps/gawk )
-	mawk? ( sys-apps/mawk )
-	nawk? ( sys-apps/nawk )
 	!app-eselect/eselect-awk
 "
 
 src_install() {
+	local alt=$(get_alternative)
 	local root_prefix=
 	use split-usr && root_prefix=../../bin/
 
 	# We could consider setting AWK=... like we do for yacc & lex,
 	# but it would need some testing with a fair amount of packages first,
 	# as autoconf prefers gawk.
-	if use busybox; then
+	case ${alt} in
+		busybox)
 			dosym "${root_prefix}busybox" /usr/bin/awk
-		newman - awk.1 <<<".so busybox.1"
-	elif use gawk; then
-		dosym gawk /usr/bin/awk
-		newman - awk.1 <<<".so gawk.1"
-	elif use mawk; then
-		dosym mawk /usr/bin/awk
-		newman - awk.1 <<<".so mawk.1"
-	elif use nawk; then
-		dosym nawk /usr/bin/awk
-		newman - awk.1 <<<".so nawk.1"
-	else
-		die "Invalid USE flag combination (broken REQUIRED_USE?)"
-	fi
+			;;
+		*)
+			dosym "${alt}" /usr/bin/awk
+			;;
+	esac
+
+	newman - awk.1 <<<".so ${alt}.1"
 
 	if use split-usr; then
 		dosym ../usr/bin/awk /bin/awk
 	fi
 }
 
+pkg_preinst() {
+	local v
+	for v in ${REPLACING_VERSIONS}; do
+		# if we are upgrading from a new enough version, leftover manpage
+		# symlink cleanup was done already
+		if ver_test "${v}" -ge 3; then
+			return
+		fi
+	done
+
+	# otherwise, remove leftover files/symlinks created by eselect-awk (sic!)
+	shopt -s nullglob
+	local files=( "${EROOT}"/usr/share/man/man1/awk.1* )
+	shopt -u nullglob
+
+	if [[ ${files[@]} ]]; then
+		einfo "Cleaning up leftover manpage symlinks from eselect-awk ..."
+		rm -v "${files[@]}" || die
+	fi
+}
+
 pkg_postrm() {
 	# make sure we don't leave the user without the symlinks, since
 	# they've not been owned by any other package