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# Copyright 2018 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
# Defines a Rust procedural macro
#
# Parameters
#
# name
# Name of the crate as defined in its manifest file. If not specified, it is
# assumed to be the same as the target name.
#
# version (optional)
# Semver version of the crate as seen on crates.io.
#
# edition (optional)
# Edition of the Rust language to be used.
# Options are "2015" and "2018". Defaults to "2018".
#
# configs (optional)
# A list of config labels applying to this target.
#
# deps (optional)
# List of rust_library GN targets on which this crate depends.
# Third party crates can be included through paths like
# "//third_party/rust_crates:<cratename>".
#
# source_root (optional)
# Location of the crate root (e.g. `src/main.rs` or `src/lib.rs`).
# This defaults to `./src/main.rs` for binaries and `./src/lib.rs` for libraries,
# and should only be changed when absolutely necessary
# (such as in the case of generated code).
#
# Example of usage:
#
# rustc_macro("foo") {
# deps = [
# "//garnet/public/rust/bar",
# "//third_party/rust_crates:serde",
# "//third_party/rust_crates:slab",
# ]
# }
template("rustc_macro") {
# Compiling procedural macros is... a bit awkward.
#
# Even though they're provided to crates that use them as if they were normal
# external crates, they're actually '.so'/'.dylib's that are compiled for the host machine
# and then linked into the compiler, so they and all their dependencies should
# be built for the host target.
#
# Once this is done, the resulting artifacts are copied into the Fuchsia target
# directories to act as if they had been built for Fuchsia. In order to avoid
# conflicts, the outputs of the original (host) artifact are built with a
# `_proc_macro` suffix added onto the end, which is removed when they're copied
# into the final target directory.
forward_variables_from(invoker, [ "visibility" ])
proc_macro_target = "${target_name}_proc_macro"
# The actual host-target build of the proc macro crate.
if (is_host) {
if (defined(invoker.name)) {
package_name = invoker.name
} else {
package_name = target_name
}
crate_name = string_replace(package_name, "-", "_")
if (!defined(invoker.source_root)) {
source_root = "src/lib.rs"
} else {
source_root = invoker.source_root
}
rust_proc_macro(proc_macro_target) {
configs = []
configs = invoker.configs
not_needed(invoker,
[
"version",
"non_rust_deps",
"force_opt",
])
crate_root = source_root
output_name = crate_name
if (defined(invoker.non_rust_deps)) {
data_deps = invoker.non_rust_deps
}
if (defined(invoker.edition) && invoker.edition == "2015") {
configs -= [ "//build/config:rust_edition_2018" ]
configs += [ "//build/config:rust_edition_2015" ]
}
forward_variables_from(invoker,
[
"deps",
"testonly",
"visibility",
])
}
} else {
not_needed(invoker, "*")
}
# redirect so that users don't need to be aware of host_toolchain requirement
group(target_name) {
public_deps = [ ":${proc_macro_target}($host_toolchain)" ]
}
}