Added a partially tested libratbag ebuild. (This a fixed and updated version from the portage tree ebuild)

dev-libs/libratbag/Manifest

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+DIST libratbag-0.13.tar.gz 242054 BLAKE2B 2058c88a033ddb85a20e73e0009723afd2b4e2a4aa89deea43c4098071dc72f8ec1a3573b7ae77dbb9d548bd45c8e2fffed0afbc413159342f0ca7cad434e859 SHA512 1ea7860dfbf83010323f81b3b47e5c3c0601548c3e84f1832edc1a66092ed2bc48f28b7b02fffa47d127db1f0f4b223e6d064c16e16b194fd8388e1a37933d4f
+EBUILD libratbag-0.13.ebuild 1263 BLAKE2B 4665e34adc3494ec1643c3fbedcd1058ab447359e610749dfad9a8ba32984fdccba973fdd37027e94b45c0aac25b0129235e0d37bd4135573e3f7914c97ac284 SHA512 2979c9280619abe8a46ff7cd778318357a365d053cb80abc18ca332241053b91c65f879d246b1793f22ee6cc66cafec602206889d357194bff16a1f2a7d06e5b

dev-libs/libratbag/libratbag-0.13.ebuild

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+# Copyright 1999-2019 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=6
+
+PYTHON_COMPAT=( python3_{4,5,6,7} )
+
+inherit meson udev python-any-r1
+
+DESCRIPTION="Library to configure gaming mice"
+HOMEPAGE="https://github.com/libratbag/libratbag"
+SRC_URI="https://github.com/${PN}/${PN}/archive/v${PV}.tar.gz -> ${P}.tar.gz"
+
+LICENSE="MIT"
+SLOT="0"
+KEYWORDS="~amd64 ~x86"
+IUSE="+systemd elogind doc test"
+RESTRICT="!test? ( test )"
+
+#REQUIRED_USE="${PYTHON_REQUIRED_USE}"
+
+DEPEND="${PYTHON_DEPS}
+	virtual/pkgconfig
+	doc? ( app-doc/doxygen )
+	systemd? ( sys-apps/systemd )
+	elogind? ( sys-auth/elogind )
+"
+RDEPEND="
+	dev-libs/libevdev
+	virtual/libudev
+"
+
+src_prepare() {
+	default
+	if use systemd && use elogind; then
+		eerror "You can not have both systemd and elogind support, they are mutually exclusive !"
+		die "Please unset one of them."
+	fi
+	sed '/default:/d' -i meson_options.txt || die
+}
+
+pkg_setup() {
+        python-any-r1_pkg_setup
+}
+
+
+src_configure() {
+	#python_setup 'python3'
+	local emesonargs=(
+		-Ddocumentation=$(usex doc true false)
+		-Dtests=$(usex test true false)
+		-Dudev-dir=$(get_udevdir)
+		-Dsystemd=$(usex systemd true false)
+		-Dlogind-provider=$(usex systemd systemd elogind)
+	)
+	meson_src_configure
+}