new eclass for R packages, taken from the R_Overlay

Signed-off-by: Alessandro Barbieri <lssndrbarbieri@gmail.com>

eclass/R-packages-guru.eclass

@@ -0,0 +1,54 @@
+# Copyright 1999-2018 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+
+inherit eutils
+
+EXPORT_FUNCTIONS src_unpack src_prepare src_compile src_install pkg_postinst
+
+SLOT="0"
+KEYWORDS="~amd64 ~x86"
+IUSE="byte-compile"
+
+DEPEND="dev-lang/R"
+RDEPEND="${DEPEND}"
+
+R-packages-guru_src_unpack() {
+	unpack ${A}
+	if [[ -d "${PN//_/.}" ]] && [[ ! -d "${P}" ]]; then
+		mv ${PN//_/.} "${P}"
+	fi
+}
+
+if has "${EAPI:-0}" 0 1 2 3 4 5; then
+	R-packages-guru_src_prepare() {
+		epatch_user
+	}
+else
+	R-packages-guru_src_prepare() {
+		default
+	}
+fi
+
+R-packages-guru_src_compile() {
+	MAKEFLAGS="CFLAGS=${CFLAGS// /\\ } CXXFLAGS=${CXXFLAGS// /\\ } FFLAGS=${FFLAGS// /\\ } FCFLAGS=${FCFLAGS// /\\ } LDFLAGS=${LDFLAGS// /\\ }" \
+		R CMD INSTALL . -l "${WORKDIR}" $(use byte-compile && echo "--byte-compile")
+}
+
+R-packages-guru_src_install() {
+	insinto /usr/$(get_libdir)/R/site-library
+	doins -r "${WORKDIR}"/${PN//_/.}
+}
+
+R-packages-guru_pkg_postinst() {
+	if [[ "${_UNRESOLVABLE_PACKAGES:-}" ]]; then
+		# _UNRESOLVABLE_PACKAGES is only set if it has more than zero items
+		local _max=${#_UNRESOLVABLE_PACKAGES[*]} i=
+
+		einfo "Dependency(-ies):"
+		for (( i=0; i<"${_max}"; i++ )); do
+			einfo "- ${_UNRESOLVABLE_PACKAGES[$i]}"
+		done
+		einfo 'are (is) suggested by upstream but could not be found.'
+		einfo 'Please install it manually from the R interpreter if you need it.'
+	fi
+}