1 files changed, 778 insertions, 0 deletions
diff --git a/dev-lang/rust/rust-1.81.0-r100.ebuild b/dev-lang/rust/rust-1.81.0-r100.ebuild
new file mode 100644
index 0000000..3af577b
--- /dev/null
+++ b/dev-lang/rust/rust-1.81.0-r100.ebuild
@@ -0,0 +1,778 @@
+# Copyright 1999-2024 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=8
+
+LLVM_COMPAT=( 18 )
+PYTHON_COMPAT=( python3_{10..13} )
+
+inherit check-reqs estack flag-o-matic llvm-r1 multiprocessing optfeature \
+	multilib multilib-build python-any-r1 rust-toolchain toolchain-funcs verify-sig
+
+if [[ ${PV} = *beta* ]]; then
+	betaver=${PV//*beta}
+	BETA_SNAPSHOT="${betaver:0:4}-${betaver:4:2}-${betaver:6:2}"
+	MY_P="rustc-beta"
+	SRC="${BETA_SNAPSHOT}/rustc-beta-src.tar.xz -> rustc-${PV}-src.tar.xz"
+else
+	MY_P="rustc-${PV}"
+	SRC="${MY_P}-src.tar.xz"
+	KEYWORDS="amd64 arm arm64 ~loong ~mips ppc ppc64 ~riscv sparc x86"
+fi
+
+RUST_STAGE0_VERSION="1.$(($(ver_cut 2) - 1)).1"
+
+DESCRIPTION="Systems programming language from Mozilla"
+HOMEPAGE="https://www.rust-lang.org/"
+
+SRC_URI="
+	https://static.rust-lang.org/dist/${SRC}
+	verify-sig? ( https://static.rust-lang.org/dist/${SRC}.asc )
+	!system-bootstrap? ( $(rust_all_arch_uris rust-${RUST_STAGE0_VERSION}) )
+"
+S="${WORKDIR}/${MY_P}-src"
+
+# keep in sync with llvm ebuild of the same version as bundled one.
+ALL_LLVM_TARGETS=( AArch64 AMDGPU ARC ARM AVR BPF CSKY DirectX Hexagon Lanai
+	LoongArch M68k Mips MSP430 NVPTX PowerPC RISCV Sparc SPIRV SystemZ VE
+	WebAssembly X86 XCore Xtensa )
+ALL_LLVM_TARGETS=( "${ALL_LLVM_TARGETS[@]/#/llvm_targets_}" )
+LLVM_TARGET_USEDEPS=${ALL_LLVM_TARGETS[@]/%/(-)?}
+
+LICENSE="|| ( MIT Apache-2.0 ) BSD BSD-1 BSD-2 BSD-4"
+SLOT="${PV}"
+
+IUSE="big-endian clippy cpu_flags_x86_sse2 debug dist doc llvm-libunwind lto miri nightly parallel-compiler rustfmt rust-analyzer rust-src system-bootstrap system-llvm test wasm ${ALL_LLVM_TARGETS[*]}"
+
+LLVM_DEPEND=()
+# splitting usedeps needed to avoid CI/pkgcheck's UncheckableDep limitation
+for _x in "${ALL_LLVM_TARGETS[@]}"; do
+	LLVM_DEPEND+=( "	${_x}? ( $(llvm_gen_dep "sys-devel/llvm:\${LLVM_SLOT}[${_x}]") )" )
+done
+LLVM_DEPEND+=( "	wasm? ( $(llvm_gen_dep 'sys-devel/lld:${LLVM_SLOT}') )" )
+LLVM_DEPEND+=( "	$(llvm_gen_dep 'sys-devel/llvm:${LLVM_SLOT}')" )
+
+# to bootstrap we need at least exactly previous version, or same.
+# most of the time previous versions fail to bootstrap with newer
+# for example 1.47.x, requires at least 1.46.x, 1.47.x is ok,
+# but it fails to bootstrap with 1.48.x
+# https://github.com/rust-lang/rust/blob/${PV}/src/stage0.json
+RUST_DEP_PREV="$(ver_cut 1).$(($(ver_cut 2) - 1))*"
+RUST_DEP_CURR="$(ver_cut 1).$(ver_cut 2)*"
+BOOTSTRAP_DEPEND="||
+	(
+		=dev-lang/rust-"${RUST_DEP_PREV}"
+		=dev-lang/rust-bin-"${RUST_DEP_PREV}"
+		=dev-lang/rust-"${RUST_DEP_CURR}"
+		=dev-lang/rust-bin-"${RUST_DEP_CURR}"
+	)
+"
+
+BDEPEND="${PYTHON_DEPS}
+	app-eselect/eselect-rust
+	|| (
+		>=sys-devel/gcc-4.7
+		>=sys-devel/clang-3.5
+	)
+	system-bootstrap? ( ${BOOTSTRAP_DEPEND} )
+	!system-llvm? (
+		>=dev-build/cmake-3.13.4
+		app-alternatives/ninja
+	)
+	test? ( dev-debug/gdb )
+	verify-sig? ( sec-keys/openpgp-keys-rust )
+"
+
+DEPEND="
+	>=app-arch/xz-utils-5.2
+	net-misc/curl:=[http2,ssl]
+	sys-libs/zlib:=
+	dev-libs/openssl:0=
+	system-llvm? (
+		${LLVM_DEPEND[*]}
+		llvm-libunwind? ( sys-libs/llvm-libunwind:= )
+	)
+	!system-llvm? (
+		!llvm-libunwind? (
+			elibc_musl? ( sys-libs/libunwind:= )
+		)
+	)
+"
+
+RDEPEND="${DEPEND}
+	app-eselect/eselect-rust
+	dev-lang/rust-common
+	sys-apps/lsb-release
+	!dev-lang/rust:stable
+	!dev-lang/rust-bin:stable
+"
+
+REQUIRED_USE="|| ( ${ALL_LLVM_TARGETS[*]} )
+	miri? ( nightly )
+	parallel-compiler? ( nightly )
+	rust-analyzer? ( rust-src )
+	test? ( ${ALL_LLVM_TARGETS[*]} )
+	wasm? ( llvm_targets_WebAssembly )
+	x86? ( cpu_flags_x86_sse2 )
+"
+
+# we don't use cmake.eclass, but can get a warning
+CMAKE_WARN_UNUSED_CLI=no
+
+QA_FLAGS_IGNORED="
+	usr/lib/${PN}/${PV}/bin/.*
+	usr/lib/${PN}/${PV}/libexec/.*
+	usr/lib/${PN}/${PV}/lib/lib.*.so
+	usr/lib/${PN}/${PV}/lib/rustlib/.*/bin/.*
+	usr/lib/${PN}/${PV}/lib/rustlib/.*/lib/lib.*.so
+"
+
+QA_SONAME="
+	usr/lib/${PN}/${PV}/lib/lib.*.so.*
+	usr/lib/${PN}/${PV}/lib/rustlib/.*/lib/lib.*.so
+"
+
+QA_PRESTRIPPED="
+	usr/lib/${PN}/${PV}/lib/rustlib/.*/bin/rust-llvm-dwp
+	usr/lib/${PN}/${PV}/lib/rustlib/.*/lib/self-contained/crtn.o
+"
+
+# An rmeta file is custom binary format that contains the metadata for the crate.
+# rmeta files do not support linking, since they do not contain compiled object files.
+# so we can safely silence the warning for this QA check.
+QA_EXECSTACK="usr/lib/${PN}/${PV}/lib/rustlib/*/lib*.rlib:lib.rmeta"
+
+# causes double bootstrap
+RESTRICT="test"
+
+VERIFY_SIG_OPENPGP_KEY_PATH=/usr/share/openpgp-keys/rust.asc
+
+PATCHES=(
+	"${FILESDIR}"/1.78.0-musl-dynamic-linking.patch
+	"${FILESDIR}"/1.74.1-cross-compile-libz.patch
+	#"${FILESDIR}"/1.72.0-bump-libc-deps-to-0.2.146.patch  # pending refresh
+	"${FILESDIR}"/1.67.0-doc-wasm.patch
+	"${FILESDIR}"/1.79.0-revert-8c40426.patch
+	"${FILESDIR}/1.81.0-backport-bug937164.patch"
+	"${FILESDIR}/1.81.0-backport-llvm-pr101761.patch"
+	"${FILESDIR}/1.81.0-backport-llvm-pr101766.patch"
+)
+
+clear_vendor_checksums() {
+	sed -i 's/\("files":{\)[^}]*/\1/' "vendor/${1}/.cargo-checksum.json" || die
+}
+
+eapply_crate() {
+	pushd "vendor/${1:?}" > /dev/null || die
+	eapply "${2:?}"
+	popd > /dev/null || die
+	clear_vendor_checksums "${1}"
+}
+
+toml_usex() {
+	usex "${1}" true false
+}
+
+bootstrap_rust_version_check() {
+	# never call from pkg_pretend. eselect-rust may be not installed yet.
+	[[ ${MERGE_TYPE} == binary ]] && return
+	local rustc_wanted="$(ver_cut 1).$(($(ver_cut 2) - 1))"
+	local rustc_toonew="$(ver_cut 1).$(($(ver_cut 2) + 1))"
+	local rustc_version=( $(eselect --brief --root="${BROOT}" rust show 2>/dev/null) )
+	rustc_version=${rustc_version[0]#rust-bin-}
+	rustc_version=${rustc_version#rust-}
+
+	[[ -z "${rustc_version}" ]] && die "Failed to determine rust version, check 'eselect rust' output"
+
+	if ver_test "${rustc_version}" -lt "${rustc_wanted}" ; then
+		eerror "Rust >=${rustc_wanted} is required"
+		eerror "please run 'eselect rust' and set correct rust version"
+		die "selected rust version is too old"
+	elif ver_test "${rustc_version}" -ge "${rustc_toonew}" ; then
+		eerror "Rust <${rustc_toonew} is required"
+		eerror "please run 'eselect rust' and set correct rust version"
+		die "selected rust version is too new"
+	else
+		einfo "Using rust ${rustc_version} to build"
+	fi
+}
+
+pre_build_checks() {
+	local M=8192
+	# multiply requirements by 1.3 if we are doing x86-multilib
+	if use amd64; then
+		M=$(( $(usex abi_x86_32 13 10) * ${M} / 10 ))
+	fi
+	M=$(( $(usex clippy 128 0) + ${M} ))
+	M=$(( $(usex miri 128 0) + ${M} ))
+	M=$(( $(usex rustfmt 256 0) + ${M} ))
+	# add 2G if we compile llvm and 256M per llvm_target
+	if ! use system-llvm; then
+		M=$(( 2048 + ${M} ))
+		local ltarget
+		for ltarget in ${ALL_LLVM_TARGETS[@]}; do
+			M=$(( $(usex ${ltarget} 256 0) + ${M} ))
+		done
+	fi
+	M=$(( $(usex wasm 256 0) + ${M} ))
+	M=$(( $(usex debug 2 1) * ${M} ))
+	eshopts_push -s extglob
+	if is-flagq '-g?(gdb)?([1-9])'; then
+		M=$(( 15 * ${M} / 10 ))
+	fi
+	eshopts_pop
+	M=$(( $(usex system-bootstrap 0 1024) + ${M} ))
+	M=$(( $(usex doc 256 0) + ${M} ))
+	CHECKREQS_DISK_BUILD=${M}M check-reqs_pkg_${EBUILD_PHASE}
+}
+
+llvm_check_deps() {
+	has_version -r "sys-devel/llvm:${LLVM_SLOT}[${LLVM_TARGET_USEDEPS// /,}]"
+}
+
+# Is LLVM being linked against libc++?
+is_libcxx_linked() {
+	local code='#include <ciso646>
+#if defined(_LIBCPP_VERSION)
+	HAVE_LIBCXX
+#endif
+'
+	local out=$($(tc-getCXX) ${CXXFLAGS} ${CPPFLAGS} -x c++ -E -P - <<<"${code}") || return 1
+	[[ ${out} == *HAVE_LIBCXX* ]]
+}
+
+pkg_pretend() {
+	pre_build_checks
+}
+
+pkg_setup() {
+	pre_build_checks
+	python-any-r1_pkg_setup
+
+	export LIBGIT2_NO_PKG_CONFIG=1 #749381
+	if tc-is-cross-compiler; then
+		export PKG_CONFIG_ALLOW_CROSS=1
+		export PKG_CONFIG_PATH="${ROOT}/usr/$(get_libdir)/pkgconfig"
+		export OPENSSL_INCLUDE_DIR="${ROOT}/usr/include"
+		export OPENSSL_LIB_DIR="${ROOT}/usr/$(get_libdir)"
+
+		use system-bootstrap || die "USE=system-bootstrap is required when cross-compiling"
+		use system-llvm && die "USE=system-llvm not allowed when cross-compiling"
+		local cross_llvm_target="$(llvm_tuple_to_target "${CBUILD}")"
+		use "llvm_targets_${cross_llvm_target}" || \
+			die "Must enable LLVM_TARGETS=${cross_llvm_target} matching CBUILD=${CBUILD} when cross-compiling"
+	fi
+
+	use system-bootstrap && bootstrap_rust_version_check
+
+	if use system-llvm; then
+		llvm-r1_pkg_setup
+
+		local llvm_config="$(get_llvm_prefix)/bin/llvm-config"
+		export LLVM_LINK_SHARED=1
+		export RUSTFLAGS="${RUSTFLAGS} -Lnative=$("${llvm_config}" --libdir)"
+	fi
+}
+
+esetup_unwind_hack() {
+	# https://bugs.gentoo.org/870280
+	# this is a hack needed to bootstrap with libgcc_s linked tarball on llvm-libunwind system.
+	# it should trigger for internal bootstrap or system-bootstrap with rust-bin.
+	# the whole idea is for stage0 to bootstrap with fake libgcc_s.
+	# final stage will receive -L${T}/lib but not -lgcc_s args, producing clean compiler.
+	local fakelib="${T}/fakelib"
+	mkdir -p "${fakelib}" || die
+	# we need both symlinks, one for cargo runtime, other for linker.
+	ln -s "${ESYSROOT}/usr/lib/libunwind.so" "${fakelib}/libgcc_s.so.1" || die
+	ln -s "${ESYSROOT}/usr/lib/libunwind.so" "${fakelib}/libgcc_s.so" || die
+	export LD_LIBRARY_PATH="${fakelib}"
+	export RUSTFLAGS+=" -L${fakelib}"
+	# this is a literally magic variable that gets through cargo cache, without it some
+	# crates ignore RUSTFLAGS.
+	# this variable can not contain leading space.
+	export MAGIC_EXTRA_RUSTFLAGS+="${MAGIC_EXTRA_RUSTFLAGS:+ }-L${fakelib}"
+}
+
+src_prepare() {
+	eapply_crate openssl-sys-0.9.92 "${FILESDIR}"/1.72.0-libressl-openssl-sys.patch
+	eapply_crate openssl-sys-0.9.102 "${FILESDIR}"/1.79.0-libressl-openssl-sys.patch
+
+	# Clear vendor checksums for crates that we patched to bump libc.
+	# NOTE: refresh this on each bump.
+	#for i in addr2line-0.20.0 bstr cranelift-jit crossbeam-channel elasticlunr-rs handlebars icu_locid libffi \
+	#	terminal_size tracing-tree; do
+	#	clear_vendor_checksums "${i}"
+	#done
+
+	if ! use system-bootstrap; then
+		has_version sys-devel/gcc || esetup_unwind_hack
+		local rust_stage0_root="${WORKDIR}"/rust-stage0
+		local rust_stage0="rust-${RUST_STAGE0_VERSION}-$(rust_abi "${CBUILD}")"
+
+		"${WORKDIR}/${rust_stage0}"/install.sh --disable-ldconfig \
+			--without=rust-docs-json-preview,rust-docs --destdir="${rust_stage0_root}" --prefix=/ || die
+	fi
+
+	default
+}
+
+src_configure() {
+	filter-lto # https://bugs.gentoo.org/862109 https://bugs.gentoo.org/866231
+
+	local rust_target="" rust_targets="" arch_cflags
+
+	# Collect rust target names to compile standard libs for all ABIs.
+	for v in $(multilib_get_enabled_abi_pairs); do
+		rust_targets+=",\"$(rust_abi $(get_abi_CHOST ${v##*.}))\""
+	done
+	if use wasm; then
+		rust_targets+=",\"wasm32-unknown-unknown\""
+		if use system-llvm; then
+			# un-hardcode rust-lld linker for this target
+			# https://bugs.gentoo.org/715348
+			sed -i '/linker:/ s/rust-lld/wasm-ld/' compiler/rustc_target/src/spec/base/wasm.rs || die
+		fi
+	fi
+	rust_targets="${rust_targets#,}"
+
+	# cargo and rustdoc are mandatory and should always be included
+	local tools='"cargo","rustdoc"'
+	use clippy && tools+=',"clippy"'
+	use miri && tools+=',"miri"'
+	use rustfmt && tools+=',"rustfmt"'
+	use rust-analyzer && tools+=',"rust-analyzer","rust-analyzer-proc-macro-srv"'
+	use rust-src && tools+=',"src"'
+
+	local rust_stage0_root
+	if use system-bootstrap; then
+		local printsysroot
+		printsysroot="$(rustc --print sysroot || die "Can't determine rust's sysroot")"
+		rust_stage0_root="${printsysroot}"
+	else
+		rust_stage0_root="${WORKDIR}"/rust-stage0
+	fi
+	# in case of prefix it will be already prefixed, as --print sysroot returns full path
+	[[ -d ${rust_stage0_root} ]] || die "${rust_stage0_root} is not a directory"
+
+	rust_target="$(rust_abi)"
+	rust_build="$(rust_abi "${CBUILD}")"
+	rust_host="$(rust_abi "${CHOST}")"
+
+	local cm_btype="$(usex debug DEBUG RELEASE)"
+	cat <<- _EOF_ > "${S}"/config.toml
+		[llvm]
+		download-ci-llvm = false
+		optimize = $(toml_usex !debug)
+		release-debuginfo = $(toml_usex debug)
+		assertions = $(toml_usex debug)
+		ninja = true
+		targets = "${LLVM_TARGETS// /;}"
+		experimental-targets = ""
+		link-shared = $(toml_usex system-llvm)
+		$(if is_libcxx_linked; then
+			# https://bugs.gentoo.org/732632
+			echo "use-libcxx = true"
+			echo "static-libstdcpp = false"
+		fi)
+		$(case "${rust_target}" in
+			i586-*-linux-*)
+				# https://github.com/rust-lang/rust/issues/93059
+				echo 'cflags = "-fcf-protection=none"'
+				echo 'cxxflags = "-fcf-protection=none"'
+				echo 'ldflags = "-fcf-protection=none"'
+				;;
+			*)
+				;;
+		esac)
+		enable-warnings = false
+		[llvm.build-config]
+		CMAKE_VERBOSE_MAKEFILE = "ON"
+		$(if ! tc-is-cross-compiler; then
+			# When cross-compiling, LLVM is compiled twice, once for host and
+			# once for target.  Unfortunately, this build configuration applies
+			# to both, which means any flags applicable to one target but not
+			# the other will break.  Conditionally disable respecting user
+			# flags when cross-compiling.
+			echo "CMAKE_C_FLAGS_${cm_btype} = \"${CFLAGS}\""
+			echo "CMAKE_CXX_FLAGS_${cm_btype} = \"${CXXFLAGS}\""
+			echo "CMAKE_EXE_LINKER_FLAGS_${cm_btype} = \"${LDFLAGS}\""
+			echo "CMAKE_MODULE_LINKER_FLAGS_${cm_btype} = \"${LDFLAGS}\""
+			echo "CMAKE_SHARED_LINKER_FLAGS_${cm_btype} = \"${LDFLAGS}\""
+			echo "CMAKE_STATIC_LINKER_FLAGS_${cm_btype} = \"${ARFLAGS}\""
+		fi)
+		[build]
+		build-stage = 2
+		test-stage = 2
+		build = "${rust_build}"
+		host = ["${rust_host}"]
+		target = [${rust_targets}]
+		cargo = "${rust_stage0_root}/bin/cargo"
+		rustc = "${rust_stage0_root}/bin/rustc"
+		rustfmt = "${rust_stage0_root}/bin/rustfmt"
+		docs = $(toml_usex doc)
+		compiler-docs = false
+		submodules = false
+		python = "${EPYTHON}"
+		locked-deps = true
+		vendor = true
+		extended = true
+		tools = [${tools}]
+		verbose = 2
+		sanitizers = false
+		profiler = true
+		cargo-native-static = false
+		[install]
+		prefix = "${EPREFIX}/usr/lib/${PN}/${PV}"
+		sysconfdir = "etc"
+		docdir = "share/doc/rust"
+		bindir = "bin"
+		libdir = "lib"
+		mandir = "share/man"
+		[rust]
+		# https://github.com/rust-lang/rust/issues/54872
+		codegen-units-std = 1
+		optimize = true
+		debug = $(toml_usex debug)
+		debug-assertions = $(toml_usex debug)
+		debug-assertions-std = $(toml_usex debug)
+		debuginfo-level = $(usex debug 2 0)
+		debuginfo-level-rustc = $(usex debug 2 0)
+		debuginfo-level-std = $(usex debug 2 0)
+		debuginfo-level-tools = $(usex debug 2 0)
+		debuginfo-level-tests = 0
+		backtrace = true
+		incremental = false
+		$(if ! tc-is-cross-compiler; then
+			echo "default-linker = \"$(tc-getCC)\""
+		fi)
+		parallel-compiler = $(toml_usex parallel-compiler)
+		channel = "$(usex nightly nightly stable)"
+		description = "gentoo"
+		rpath = false
+		verbose-tests = true
+		optimize-tests = $(toml_usex !debug)
+		codegen-tests = true
+		dist-src = false
+		remap-debuginfo = true
+		lld = $(usex system-llvm false $(toml_usex wasm))
+		# only deny warnings if doc+wasm are NOT requested, documenting stage0 wasm std fails without it
+		# https://github.com/rust-lang/rust/issues/74976
+		# https://github.com/rust-lang/rust/issues/76526
+		deny-warnings = $(usex wasm $(usex doc false true) true)
+		backtrace-on-ice = true
+		jemalloc = false
+		# See https://github.com/rust-lang/rust/issues/121124
+		lto = "$(usex lto thin off)"
+		[dist]
+		src-tarball = false
+		compression-formats = ["xz"]
+		compression-profile = "balanced"
+	_EOF_
+
+	for v in $(multilib_get_enabled_abi_pairs); do
+		rust_target=$(rust_abi $(get_abi_CHOST ${v##*.}))
+		arch_cflags="$(get_abi_CFLAGS ${v##*.})"
+
+		export CFLAGS_${rust_target//-/_}="${arch_cflags}"
+
+		cat <<- _EOF_ >> "${S}"/config.toml
+			[target.${rust_target}]
+			ar = "$(tc-getAR)"
+			cc = "$(tc-getCC)"
+			cxx = "$(tc-getCXX)"
+			linker = "$(tc-getCC)"
+			ranlib = "$(tc-getRANLIB)"
+			llvm-libunwind = "$(usex llvm-libunwind $(usex system-llvm system in-tree) no)"
+		_EOF_
+		if use system-llvm; then
+			cat <<- _EOF_ >> "${S}"/config.toml
+				llvm-config = "$(get_llvm_prefix)/bin/llvm-config"
+			_EOF_
+		fi
+		# by default librustc_target/spec/linux_musl_base.rs sets base.crt_static_default = true;
+		# but we patch it and set to false here as well
+		if use elibc_musl; then
+			cat <<- _EOF_ >> "${S}"/config.toml
+				crt-static = false
+				musl-root = "$($(tc-getCC) -print-sysroot)/usr"
+			_EOF_
+		fi
+	done
+	if use wasm; then
+		wasm_target="wasm32-unknown-unknown"
+		export CFLAGS_${wasm_target//-/_}="$(filter-flags '-mcpu*' '-march*' '-mtune*'; echo "$CFLAGS")"
+		cat <<- _EOF_ >> "${S}"/config.toml
+			[target.wasm32-unknown-unknown]
+			linker = "$(usex system-llvm lld rust-lld)"
+			# wasm target does not have profiler_builtins https://bugs.gentoo.org/848483
+			profiler = false
+		_EOF_
+	fi
+
+	if [[ -n ${I_KNOW_WHAT_I_AM_DOING_CROSS} ]]; then # whitespace intentionally shifted below
+	# experimental cross support
+	# discussion: https://bugs.gentoo.org/679878
+	# TODO: c*flags, clang, system-llvm, cargo.eclass target support
+	# it would be much better if we could split out stdlib
+	# complilation to separate ebuild and abuse CATEGORY to
+	# just install to /usr/lib/rustlib/<target>
+
+	# extra targets defined as a bash array
+	# spec format:  <LLVM target>:<rust-target>:<CTARGET>
+	# best place would be /etc/portage/env/dev-lang/rust
+	# Example:
+	# RUST_CROSS_TARGETS=(
+	#	"AArch64:aarch64-unknown-linux-gnu:aarch64-unknown-linux-gnu"
+	# )
+	# no extra hand holding is done, no target transformations, all
+	# values are passed as-is with just basic checks, so it's up to user to supply correct values
+	# valid rust targets can be obtained with
+	# 	rustc --print target-list
+	# matching cross toolchain has to be installed
+	# matching LLVM_TARGET has to be enabled for both rust and llvm (if using system one)
+	# only gcc toolchains installed with crossdev are checked for now.
+
+	# BUG: we can't pass host flags to cross compiler, so just filter for now
+	# BUG: this should be more fine-grained.
+	filter-flags '-mcpu=*' '-march=*' '-mtune=*'
+
+	local cross_target_spec
+	for cross_target_spec in "${RUST_CROSS_TARGETS[@]}";do
+		# extracts first element form <LLVM target>:<rust-target>:<CTARGET>
+		local cross_llvm_target="${cross_target_spec%%:*}"
+		# extracts toolchain triples, <rust-target>:<CTARGET>
+		local cross_triples="${cross_target_spec#*:}"
+		# extracts first element after before : separator
+		local cross_rust_target="${cross_triples%%:*}"
+		# extracts last element after : separator
+		local cross_toolchain="${cross_triples##*:}"
+		use llvm_targets_${cross_llvm_target} || die "need llvm_targets_${cross_llvm_target} target enabled"
+		command -v ${cross_toolchain}-gcc > /dev/null 2>&1 || die "need ${cross_toolchain} cross toolchain"
+
+		cat <<- _EOF_ >> "${S}"/config.toml
+			[target.${cross_rust_target}]
+			ar = "${cross_toolchain}-ar"
+			cc = "${cross_toolchain}-gcc"
+			cxx = "${cross_toolchain}-g++"
+			linker = "${cross_toolchain}-gcc"
+			ranlib = "${cross_toolchain}-ranlib"
+		_EOF_
+		if use system-llvm; then
+			cat <<- _EOF_ >> "${S}"/config.toml
+				llvm-config = "$(get_llvm_prefix)/bin/llvm-config"
+			_EOF_
+		fi
+		if [[ "${cross_toolchain}" == *-musl* ]]; then
+			cat <<- _EOF_ >> "${S}"/config.toml
+				musl-root = "$(${cross_toolchain}-gcc -print-sysroot)/usr"
+			_EOF_
+		fi
+
+		# append cross target to "normal" target list
+		# example 'target = ["powerpc64le-unknown-linux-gnu"]'
+		# becomes 'target = ["powerpc64le-unknown-linux-gnu","aarch64-unknown-linux-gnu"]'
+
+		rust_targets="${rust_targets},\"${cross_rust_target}\""
+		sed -i "/^target = \[/ s#\[.*\]#\[${rust_targets}\]#" config.toml || die
+
+		ewarn
+		ewarn "Enabled ${cross_rust_target} rust target"
+		ewarn "Using ${cross_toolchain} cross toolchain"
+		ewarn
+		if ! has_version -b 'sys-devel/binutils[multitarget]' ; then
+			ewarn "'sys-devel/binutils[multitarget]' is not installed"
+			ewarn "'strip' will be unable to strip cross libraries"
+			ewarn "cross targets will be installed with full debug information"
+			ewarn "enable 'multitarget' USE flag for binutils to be able to strip object files"
+			ewarn
+			ewarn "Alternatively llvm-strip can be used, it supports stripping any target"
+			ewarn "define STRIP=\"llvm-strip\" to use it (experimental)"
+			ewarn
+		fi
+	done
+	fi # I_KNOW_WHAT_I_AM_DOING_CROSS
+
+	einfo "Rust configured with the following flags:"
+	echo
+	echo RUSTFLAGS="\"${RUSTFLAGS}\""
+	echo RUSTFLAGS_BOOTSTRAP="\"${RUSTFLAGS_BOOTSTRAP}\""
+	echo RUSTFLAGS_NOT_BOOTSTRAP="\"${RUSTFLAGS_NOT_BOOTSTRAP}\""
+	echo MAGIC_EXTRA_RUSTFLAGS="\"${MAGIC_EXTRA_RUSTFLAGS}\""
+	env | grep "CARGO_TARGET_.*_RUSTFLAGS="
+	env | grep "CFLAGS_.*"
+	echo
+	einfo "config.toml contents:"
+	cat "${S}"/config.toml || die
+	echo
+}
+
+src_compile() {
+	RUST_BACKTRACE=1 "${EPYTHON}" ./x.py build -vvv --config="${S}"/config.toml -j$(makeopts_jobs) || die
+}
+
+src_test() {
+	# https://rustc-dev-guide.rust-lang.org/tests/intro.html
+
+	# those are basic and codegen tests.
+	local tests=(
+		codegen
+		codegen-units
+		compile-fail
+		incremental
+		mir-opt
+		pretty
+		run-make
+	)
+
+	# fails if llvm is not built with ALL targets.
+	# and known to fail with system llvm sometimes.
+	use system-llvm || tests+=( assembly )
+
+	# fragile/expensive/less important tests
+	# or tests that require extra builds
+	# TODO: instead of skipping, just make some nonfatal.
+	if [[ ${ERUST_RUN_EXTRA_TESTS:-no} != no ]]; then
+		tests+=(
+			rustdoc
+			rustdoc-js
+			rustdoc-js-std
+			rustdoc-ui
+			run-make-fulldeps
+			ui
+			ui-fulldeps
+		)
+	fi
+
+	local i failed=()
+	einfo "rust_src_test: enabled tests ${tests[@]/#/src/test/}"
+	for i in "${tests[@]}"; do
+		local t="src/test/${i}"
+		einfo "rust_src_test: running ${t}"
+		if ! RUST_BACKTRACE=1 "${EPYTHON}" ./x.py test -vv --config="${S}"/config.toml \
+				-j$(makeopts_jobs) --no-doc --no-fail-fast "${t}"
+		then
+				failed+=( "${t}" )
+				eerror "rust_src_test: ${t} failed"
+		fi
+	done
+
+	if [[ ${#failed[@]} -ne 0 ]]; then
+		eerror "rust_src_test: failure summary: ${failed[@]}"
+		die "aborting due to test failures"
+	fi
+}
+
+src_install() {
+	DESTDIR="${D}" "${EPYTHON}" ./x.py install -vv --config="${S}"/config.toml -j$(makeopts_jobs) || die
+
+	# bug #689562, #689160
+	rm -v "${ED}/usr/lib/${PN}/${PV}/etc/bash_completion.d/cargo" || die
+	rmdir -v "${ED}/usr/lib/${PN}/${PV}"/etc{/bash_completion.d,} || die
+
+	local symlinks=(
+		cargo
+		rustc
+		rustdoc
+		rust-gdb
+		rust-gdbgui
+		rust-lldb
+	)
+
+	use clippy && symlinks+=( clippy-driver cargo-clippy )
+	use miri && symlinks+=( miri cargo-miri )
+	use rustfmt && symlinks+=( rustfmt cargo-fmt )
+	use rust-analyzer && symlinks+=( rust-analyzer )
+
+	einfo "installing eselect-rust symlinks and paths: ${symlinks[@]}"
+	local i
+	for i in "${symlinks[@]}"; do
+		# we need realpath on /usr/bin/* symlink return version-appended binary path.
+		# so /usr/bin/rustc should point to /usr/lib/rust/<ver>/bin/rustc-<ver>
+		# need to fix eselect-rust to remove this hack.
+		local ver_i="${i}-${PV}"
+		if [[ -f "${ED}/usr/lib/${PN}/${PV}/bin/${i}" ]]; then
+			einfo "Installing ${i} symlink"
+			ln -v "${ED}/usr/lib/${PN}/${PV}/bin/${i}" "${ED}/usr/lib/${PN}/${PV}/bin/${ver_i}" || die
+		else
+			ewarn "${i} symlink requested, but source file not found"
+			ewarn "please report this"
+		fi
+		dosym "../lib/${PN}/${PV}/bin/${ver_i}" "/usr/bin/${ver_i}"
+	done
+
+	# symlinks to switch components to active rust in eselect
+	dosym "${PV}/lib" "/usr/lib/${PN}/lib-${PV}"
+	dosym "${PV}/libexec" "/usr/lib/${PN}/libexec-${PV}"
+	dosym "${PV}/share/man" "/usr/lib/${PN}/man-${PV}"
+	dosym "rust/${PV}/lib/rustlib" "/usr/lib/rustlib-${PV}"
+	dosym "../../lib/${PN}/${PV}/share/doc/rust" "/usr/share/doc/${P}"
+
+	newenvd - "50${P}" <<-_EOF_
+		LDPATH="${EPREFIX}/usr/lib/rust/lib-${PV}"
+		MANPATH="${EPREFIX}/usr/lib/rust/man-${PV}"
+	_EOF_
+
+	rm -rf "${ED}/usr/lib/${PN}/${PV}"/*.old || die
+	rm -rf "${ED}/usr/lib/${PN}/${PV}/bin"/*.old || die
+	rm -rf "${ED}/usr/lib/${PN}/${PV}/doc"/*.old || die
+
+	# note: eselect-rust adds EROOT to all paths below
+	cat <<-_EOF_ > "${T}/provider-${P}"
+		/usr/bin/cargo
+		/usr/bin/rustdoc
+		/usr/bin/rust-gdb
+		/usr/bin/rust-gdbgui
+		/usr/bin/rust-lldb
+		/usr/lib/rustlib
+		/usr/lib/rust/lib
+		/usr/lib/rust/libexec
+		/usr/lib/rust/man
+		/usr/share/doc/rust
+	_EOF_
+
+	if use clippy; then
+		echo /usr/bin/clippy-driver >> "${T}/provider-${P}"
+		echo /usr/bin/cargo-clippy >> "${T}/provider-${P}"
+	fi
+	if use miri; then
+		echo /usr/bin/miri >> "${T}/provider-${P}"
+		echo /usr/bin/cargo-miri >> "${T}/provider-${P}"
+	fi
+	if use rustfmt; then
+		echo /usr/bin/rustfmt >> "${T}/provider-${P}"
+		echo /usr/bin/cargo-fmt >> "${T}/provider-${P}"
+	fi
+	if use rust-analyzer; then
+		echo /usr/bin/rust-analyzer >> "${T}/provider-${P}"
+	fi
+
+	insinto /etc/env.d/rust
+	doins "${T}/provider-${P}"
+
+	if use dist; then
+		"${EPYTHON}" ./x.py dist -vv --config="${S}"/config.toml -j$(makeopts_jobs) || die
+		insinto "/usr/lib/${PN}/${PV}/dist"
+		doins -r "${S}/build/dist/."
+	fi
+}
+
+pkg_postinst() {
+	eselect rust update
+
+	if has_version dev-debug/gdb || has_version dev-debug/lldb; then
+		elog "Rust installs a helper script for calling GDB and LLDB,"
+		elog "for your convenience it is installed under /usr/bin/rust-{gdb,lldb}-${PV}."
+	fi
+
+	if has_version app-editors/emacs; then
+		optfeature "emacs support for rust" app-emacs/rust-mode
+	fi
+
+	if has_version app-editors/gvim || has_version app-editors/vim; then
+		optfeature "vim support for rust" app-vim/rust-vim
+	fi
+}
+
+pkg_postrm() {
+	eselect rust cleanup
+}