unpacker.eclass: Workaround zstd refusing to process symlinks

Closes: https://bugs.gentoo.org/873352
Signed-off-by: Michał Górny <[email protected]>

eclass/tests/unpacker.sh

@@ -42,9 +42,14 @@ test_unpack() {
 	eval "${packcmd}"
 	assert "packing ${archive} failed"
 	cd testdir || die
+
+	# create a symlink to flush out compressor issues and resemble distdir more
+	# https://bugs.gentoo.org/873352
+	ln -s "../${archive}" "${archive}" || die
+
 	local out
 	out=$(
-		_unpacker "../${archive}" 2>&1
+		_unpacker "${archive}" 2>&1
 	)
 	ret=$?
 	if [[ ${ret} -eq 0 ]]; then

eclass/unpacker.eclass

@@ -523,11 +523,11 @@ _unpacker() {
 	if [[ -z ${arch} ]] ; then
 		# Need to decompress the file into $PWD #408801
 		local _a=${a%.*}
-		${comp} "${a}" > "${_a##*/}"
+		${comp} < "${a}" > "${_a##*/}"
 	elif [[ -z ${comp} ]] ; then
 		${arch} "${a}"
 	else
-		${comp} "${a}" | ${arch} -
+		${comp} < "${a}" | ${arch} -
 	fi
 
 	assert "unpacking ${a} failed (comp=${comp} arch=${arch})"