gui-wm/river: fix Zig version detection in 0.3.5

It used zig version selected by user in `eselect-zig` previously,
which is incorrect, as ebuild should use own, detected Zig version.

Seems like this logic is also copy-pasted from
2724ddc753/gui-wm/river/river-0.3.2.ebuild ,
which, in its turn, has old logic from sys-fs/ncdu. Not critical, but
fixed this too.

Signed-off-by: Eric Joldasov <bratishkaerik@landless-city.net>

gui-wm/river/river-0.3.5.ebuild

@@ -28,6 +28,7 @@ KEYWORDS="~amd64"
 IUSE="+llvm +man pie xwayland bash-completion zsh-completion fish-completion"
 
 EZIG_MIN="0.12"
+EZIG_MAX_EXCLUSIVE="0.13"
 
 DEPEND="
 	|| ( dev-lang/zig-bin:${EZIG_MIN} dev-lang/zig:${EZIG_MIN} )
@@ -39,12 +40,69 @@ DEPEND="
 "
 RDEPEND="${DEPEND}"
 
+DOCS=( README.md )
+
 # https://github.com/ziglang/zig/issues/3382
 QA_FLAGS_IGNORED="usr/bin/*"
 
-ezig_build() {
-	EZIG=zig
-	edo "${EZIG}" build "${ZIG_BUILD_ARGS[@]}" "${@}"
+# Many thanks to Florian Schmaus (Flowdalic)!
+# Adapted from https://github.com/gentoo/gentoo/pull/28986
+# Set the EZIG environment variable.
+zig-set_EZIG() {
+	[[ -n ${EZIG} ]] && return
+
+	local candidate selected selected_ver ver
+
+	for candidate in "${BROOT}"/usr/bin/zig-*; do
+		if [[ ! -L ${candidate} || ${candidate} != */zig?(-bin)-+([0-9.]) ]]; then
+			continue
+		fi
+
+		ver=${candidate##*-}
+
+		if [[ -n ${EZIG_EXACT_VER} ]]; then
+			ver_test "${ver}" -ne "${EZIG_EXACT_VER}" && continue
+
+			selected="${candidate}"
+			selected_ver="${ver}"
+			break
+		fi
+
+		if [[ -n ${EZIG_MIN} ]] \
+			   && ver_test "${ver}" -lt "${EZIG_MIN}"; then
+			# Candidate does not satisfy EZIG_MIN condition.
+			continue
+		fi
+
+		if [[ -n ${EZIG_MAX_EXCLUSIVE} ]] \
+			   && ver_test "${ver}" -ge "${EZIG_MAX_EXCLUSIVE}"; then
+			# Candidate does not satisfy EZIG_MAX_EXCLUSIVE condition.
+			continue
+		fi
+
+		if [[ -n ${selected_ver} ]] \
+			   && ver_test "${selected_ver}" -gt "${ver}"; then
+			# Candidate is older than the currently selected candidate.
+			continue
+		fi
+
+		selected="${candidate}"
+		selected_ver="${ver}"
+	done
+
+	if [[ -z ${selected} ]]; then
+		die "Could not find (suitable) zig installation in ${BROOT}/usr/bin"
+	fi
+
+	export EZIG="${selected}"
+	export EZIG_VER="${selected_ver}"
+}
+
+# Invoke zig with the optionally provided arguments.
+ezig() {
+	zig-set_EZIG
+
+	edo "${EZIG}" "${@}"
 }
 
 src_unpack() {
@@ -58,7 +116,8 @@ src_unpack() {
 }
 
 src_configure() {
-	export ZIG_BUILD_ARGS=(
+	export ZBS_ARGS=(
+		--prefix usr/
 		-Doptimize=ReleaseSafe
 
 		-Dpie=$(usex pie true false)
@@ -72,17 +131,16 @@ src_configure() {
 }
 
 src_compile() {
-	ezig_build
+	ezig build "${ZBS_ARGS[@]}"
 }
 
 src_test() {
-	ezig_build test
+	ezig build test "${ZBS_ARGS[@]}"
 }
 
 src_install() {
-	ezig_build install --prefix "${ED}/usr"
-
-	dodoc README.md
+	DESTDIR="${ED}" ezig build install "${ZBS_ARGS[@]}"
+	einstalldocs
 
 	insinto /usr/share/wayland-sessions
 	doins contrib/river.desktop