cargo.eclass: Sync with Gentoo

Signed-off-by: James Le Cuirot <jlecuirot@microsoft.com>

sdk_container/src/third_party/portage-stable/eclass/cargo.eclass

@@ -109,7 +109,7 @@ ECARGO_VENDOR="${ECARGO_HOME}/gentoo"
 #
 # If you enable CARGO_OPTIONAL, you have to set BDEPEND on virtual/rust
 # for your package and call at least cargo_gen_config manually before using
-# other src_functions of this eclass.
+# other src_functions or cargo_env of this eclass.
 # Note that cargo_gen_config is automatically called by cargo_src_unpack.
 
 # @ECLASS_VARIABLE: myfeatures
@@ -248,7 +248,7 @@ cargo_crate_uris() {
 
 # @FUNCTION: cargo_gen_config
 # @DESCRIPTION:
-# Generate the $CARGO_HOME/config necessary to use our local registry and settings.
+# Generate the $CARGO_HOME/config.toml necessary to use our local registry and settings.
 # Cargo can also be configured through environment variables in addition to the TOML syntax below.
 # For each configuration key below of the form foo.bar the environment variable CARGO_FOO_BAR
 # can also be used to define the value.
@@ -261,7 +261,7 @@ cargo_gen_config() {
 
 	mkdir -p "${ECARGO_HOME}" || die
 
-	cat > "${ECARGO_HOME}/config" <<- _EOF_ || die "Failed to create cargo config"
+	cat > "${ECARGO_HOME}/config.toml" <<- _EOF_ || die "Failed to create cargo config"
 	[source.gentoo]
 	directory = "${ECARGO_VENDOR}"
 
@@ -324,9 +324,7 @@ _cargo_gen_git_config() {
 # Return the directory within target that contains the build, e.g.
 # target/aarch64-unknown-linux-gnu/release.
 cargo_target_dir() {
-	local abi
-	tc-is-cross-compiler && abi=/$(rust_abi)
-	echo "${CARGO_TARGET_DIR:-target}${abi}/$(usex debug debug release)"
+	echo "${CARGO_TARGET_DIR:-target}/$(rust_abi)/$(usex debug debug release)"
 }
 
 # @FUNCTION: cargo_src_unpack
@@ -523,36 +521,92 @@ cargo_src_configure() {
 	[[ ${ECARGO_ARGS[@]} ]] && einfo "Configured with: ${ECARGO_ARGS[@]}"
 }
 
+# @FUNCTION: cargo_env
+# @USAGE: Command with its arguments
+# @DESCRIPTION:
+# Run the given command under an environment needed for performing tasks with
+# Cargo such as building. RUSTFLAGS are appended to additional flags set here.
+# Ensure these are set consistently between Cargo invocations, otherwise
+# rebuilds will occur. Project-specific rustflags set against [build] will not
+# take affect due to Cargo limitations, so add these to your ebuild's RUSTFLAGS
+# if they seem important.
+cargo_env() {
+	[[ ${_CARGO_GEN_CONFIG_HAS_RUN} ]] || \
+		die "FATAL: please call cargo_gen_config before using ${FUNCNAME}"
+
+	# Shadow flag variables so that filtering below remains local.
+	local flag
+	for flag in $(all-flag-vars); do
+		local -x "${flag}=${!flag}"
+	done
+
+	# Rust extensions are incompatible with C/C++ LTO compiler see e.g.
+	# https://bugs.gentoo.org/910220
+	filter-lto
+
+	tc-export AR CC CXX PKG_CONFIG
+
+	# Set vars for cc-rs crate.
+	local -x \
+		HOST_AR=$(tc-getBUILD_AR)
+		HOST_CC=$(tc-getBUILD_CC)
+		HOST_CXX=$(tc-getBUILD_CXX)
+		HOST_CFLAGS=${BUILD_CFLAGS}
+		HOST_CXXFLAGS=${BUILD_CXXFLAGS}
+
+	# Unfortunately, Cargo is *really* bad at handling flags. In short, it uses
+	# the first of the RUSTFLAGS env var, any target-specific config, and then
+	# any generic [build] config. It can merge within the latter two types from
+	# different sources, but it will not merge across these different types, so
+	# if a project sets flags under [target.'cfg(all())'], it will override any
+	# flags we set under [build] and vice-versa.
+	#
+	# It has been common for users and ebuilds to set RUSTFLAGS, which would
+	# have overridden whatever a project sets anyway, so the least-worst option
+	# is to include those RUSTFLAGS in target-specific config here, which will
+	# merge with any the project sets. Only flags in generic [build] config set
+	# by the project will be lost, and ebuilds will need to add those to
+	# RUSTFLAGS themselves if they are important.
+	#
+	# We could potentially inspect a project's generic [build] config and
+	# reapply those flags ourselves, but that would require a proper toml parser
+	# like tomlq, it might lead to confusion where projects also have
+	# target-specific config, and converting arrays to strings may not work
+	# well. Nightly features to inspect the config might help here in future.
+	#
+	# As of Rust 1.80, it is not possible to set separate flags for the build
+	# host and the target host when cross-compiling. The flags given are applied
+	# to the target host only with no flags being applied to the build host. The
+	# nightly host-config feature will improve this situation later.
+	#
+	# The default linker is "cc" so override by setting linker to CC in the
+	# RUSTFLAGS. The given linker cannot include any arguments, so split these
+	# into link-args along with LDFLAGS.
+	local -x CARGO_BUILD_TARGET=$(rust_abi)
+	local TRIPLE=${CARGO_BUILD_TARGET//-/_}
+	local TRIPLE=${TRIPLE^^} LD_A=( $(tc-getCC) ${LDFLAGS} )
+	local -x CARGO_TARGET_"${TRIPLE}"_RUSTFLAGS="-C strip=none -C linker=${LD_A[0]}"
+	[[ ${#LD_A[@]} -gt 1 ]] && local CARGO_TARGET_"${TRIPLE}"_RUSTFLAGS+="$(printf -- ' -C link-arg=%s' "${LD_A[@]:1}")"
+	local CARGO_TARGET_"${TRIPLE}"_RUSTFLAGS+=" ${RUSTFLAGS}"
+
+	(
+		# These variables will override the above, even if empty, so unset them
+		# locally. Do this in a subshell so that they remain set afterwards.
+		unset CARGO_BUILD_RUSTFLAGS CARGO_ENCODED_RUSTFLAGS RUSTFLAGS
+
+		"${@}"
+	)
+}
+
 # @FUNCTION: cargo_src_compile
 # @DESCRIPTION:
 # Build the package using cargo build.
 cargo_src_compile() {
 	debug-print-function ${FUNCNAME} "$@"
 
-	[[ ${_CARGO_GEN_CONFIG_HAS_RUN} ]] || \
-		die "FATAL: please call cargo_gen_config before using ${FUNCNAME}"
-
-	filter-lto
-	tc-export AR CC CXX PKG_CONFIG
-
-	if tc-is-cross-compiler; then
-		export CARGO_BUILD_TARGET=$(rust_abi)
-		local TRIPLE=${CARGO_BUILD_TARGET//-/_}
-		export CARGO_TARGET_"${TRIPLE^^}"_LINKER=$(tc-getCC)
-
-		# Set vars for cc-rs crate.
-		tc-export_build_env
-		export \
-			HOST_AR=$(tc-getBUILD_AR)
-			HOST_CC=$(tc-getBUILD_CC)
-			HOST_CXX=$(tc-getBUILD_CXX)
-			HOST_CFLAGS=${BUILD_CFLAGS}
-			HOST_CXXFLAGS=${BUILD_CXXFLAGS}
-	fi
-
 	set -- cargo build $(usex debug "" --release) ${ECARGO_ARGS[@]} "$@"
 	einfo "${@}"
-	"${@}" || die "cargo build failed"
+	cargo_env "${@}" || die "cargo build failed"
 }
 
 # @FUNCTION: cargo_src_install
@@ -564,16 +618,13 @@ cargo_src_compile() {
 cargo_src_install() {
 	debug-print-function ${FUNCNAME} "$@"
 
-	[[ ${_CARGO_GEN_CONFIG_HAS_RUN} ]] || \
-		die "FATAL: please call cargo_gen_config before using ${FUNCNAME}"
-
 	set -- cargo install $(has --path ${@} || echo --path ./) \
 		--root "${ED}/usr" \
 		${GIT_CRATES[@]:+--frozen} \
 		$(usex debug --debug "") \
 		${ECARGO_ARGS[@]} "$@"
 	einfo "${@}"
-	"${@}" || die "cargo install failed"
+	cargo_env "${@}" || die "cargo install failed"
 
 	rm -f "${ED}/usr/.crates.toml" || die
 	rm -f "${ED}/usr/.crates2.json" || die
@@ -585,12 +636,9 @@ cargo_src_install() {
 cargo_src_test() {
 	debug-print-function ${FUNCNAME} "$@"
 
-	[[ ${_CARGO_GEN_CONFIG_HAS_RUN} ]] || \
-		die "FATAL: please call cargo_gen_config before using ${FUNCNAME}"
-
 	set -- cargo test $(usex debug "" --release) ${ECARGO_ARGS[@]} "$@"
 	einfo "${@}"
-	"${@}" || die "cargo test failed"
+	cargo_env "${@}" || die "cargo test failed"
 }
 
 fi