eclass/coreos-cargo: Add eclass for cross-compiling with cargo

This should be a drop-in replacement for cargo.eclass.

sdk_container/src/third_party/coreos-overlay/eclass/coreos-cargo.eclass

@@ -0,0 +1,77 @@
+# Copyright 2017 CoreOS, Inc.
+# Distributed under the terms of the GNU General Public License v2
+
+# @ECLASS: coreos-cargo.eclass
+# @MAINTAINER:
+# team-os@coreos.com
+# @AUTHOR:
+# David Michael <david.michael@coreos.com>
+# @BLURB: cargo cross-compilation support for CoreOS/ChromeOS targets
+
+if [[ -z ${_COREOS_CARGO_ECLASS} ]]; then
+_COREOS_CARGO_ECLASS=1
+
+# XXX: Don't require host dependencies to also be in the sysroot.
+CATEGORY=dev-util PN=cargo inherit cargo
+inherit toolchain-funcs
+
+EXPORT_FUNCTIONS src_unpack
+
+[[ ${CATEGORY}/${PN} != dev-libs/rustlib ]] && DEPEND="|| (
+	dev-libs/rustlib
+	dev-util/cargo
+)"
+
+# @FUNCTION: coreos-cargo_src_unpack
+# @DESCRIPTION:
+# This amends the src_unpack from cargo.eclass to add support for Rust
+# cross-compiling to the ChromeOS targets.  It maps the host triplet to
+# one built into rustc and uses the board root as its sysroot.
+coreos-cargo_src_unpack() {
+	debug-print-function ${FUNCNAME} "$@"
+	cargo_src_unpack "$@"
+
+	[[ ${CBUILD:-${CHOST}} != ${CHOST} ]] || return 0
+
+	# Define the cross-compilers for rust-gcc commands.
+	export TARGET_AR="$(tc-getAR)"
+	export TARGET_CC="$(tc-getCC)"
+	export TARGET_CFLAGS="${CFLAGS}"
+	export TARGET_CXX="$(tc-getCXX)"
+	export TARGET_CXXFLAGS="${CXXFLAGS}"
+
+	# Map the SDK host triplet to one that is built into rustc.
+	function rust_builtin_target() case "$1" in
+		aarch64-*-linux-gnu) echo aarch64-unknown-linux-gnu ;;
+		x86_64-*-linux-gnu) echo x86_64-unknown-linux-gnu ;;
+		*) die "Unknown host triplet: $1" ;;
+	esac
+
+	# Allow searching host libraries when targeting incompatible systems.
+	export RUST_TARGET=$(rust_builtin_target "${CHOST}")
+	local build_triplet=$(rust_builtin_target "${CBUILD}")
+	[[ ${RUST_TARGET} = ${build_triplet} ]] ||
+	local crossflags="-L /usr/lib64/rustlib/${build_triplet}/lib"
+
+	# Create a compiler wrapper to work around rust-lang/cargo#4456.
+	if [[ ${CATEGORY}/${PN} != dev-libs/rustlib ]]; then
+		cat <<- EOF > "${T}/wrustc" && chmod 0755 "${T}/wrustc"
+		#!/bin/sh
+		exec rustc --sysroot="${ROOT:-/}usr" ${crossflags-} "\$@"
+		EOF
+		export RUSTC="${T}/wrustc"
+	fi
+
+	# Compile for the built-in target, using the SDK cross-tools.
+	cat <<- EOF >> "${ECARGO_HOME}/config"
+
+	[build]
+	target = "${RUST_TARGET}"
+
+	[target.${RUST_TARGET}]
+	ar = "${TARGET_AR}"
+	linker = "${TARGET_CC}"
+	EOF
+}
+
+fi