# Copyright 2021 The Chromium Project. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import("//build/config/chrome_build.gni")
import("//build/config/compiler/compiler.gni")
import("//build/toolchain/toolchain.gni")

if (is_android) {
  import("//build/config/android/config.gni")
}

declare_args() {
  # Whether to allow Rust code to be part of the Chromium *build process*.
  # This can be used to create Rust test binaries, even if the flag below
  # is false.
  enable_rust = false

  # Whether to allow Rust code to contribute to the main Chromium binaries.
  enable_rust_in_chromium = false

  # Use unverified, untrusted, Rust toolchains from the internet
  # (which support more platforms and options than those we trust for real
  # builds).
  use_unverified_rust_toolchain = false

  # If using an unverified Rust toolchain, use this prefix for where to find
  # the binaries.
  rust_bin_dir = ""

  # Use LTO when using rustc to link binaries. Experimental. Currently incompatible
  # with the options we use in our C++ toolchain to split LTO units.
  # This has no effect on the production of normal Chrome binaries, which are
  # linked by clang/lld rather than rustc.
  # https://crbug.com/1229419
  use_lto_in_rustc_linking = false

  # Use goma for Rust builds. Experimental. The only known problem is
  # b/193072381, but then again, we don't expect a build speedup before much
  # more work is done.
  use_goma_rust = false
}

# Rust code may end up being linked into a final executable by:
# * rustc (which calls lld)
# * our pre-existing C++ linker invocations
# At the moment, this first pipeline is incompatible with the ldflags we use
# for thin LTO, due to some problem in escaping gn rules. There's a further
# problem with -lunwind on Android.
# However, Rust code is still useful if it's contributing to our existing
# C++ linker invocations, so this doesn't disable Rust entirely. It does
# disable Rust unit test executables, so we do need to fix this.
# https://crbug.com/1229423
rustc_can_link = !use_thin_lto && !is_android

# Has a Rust toolchain available in the build by default.
toolchain_has_official_rust =
    (!is_nacl &&
     (is_android && (target_cpu == "arm" || target_cpu == "arm64" ||
                     target_cpu == "x64" || target_cpu == "x86"))) ||
    (is_linux && target_cpu == "x64")

toolchain_has_rust = enable_rust && (toolchain_has_official_rust ||
                                     use_unverified_rust_toolchain)

# We use the Rust linker for building test executables, so we only build them
# if we're able to use the Rust linker. We could use the C++ linker for this
# too, we've just not set up GN to do so at the moment.
build_rust_unit_tests = rustc_can_link

if (use_unverified_rust_toolchain) {
  assert(rust_bin_dir != "")
  rust_prefix = "$rust_bin_dir/"
} else if (toolchain_has_official_rust) {
  if (host_os != "linux") {
#     assert(false,
#            "Attempt to use standard Rust toolchain on an unsupported platform")
  }
  rust_prefix =
      rebase_path("//third_party/android_rust_toolchain/toolchain/1.54.0/bin/")
}

assert(!toolchain_has_rust || defined(rust_prefix))

# Figure out the Rust target triple (aka 'rust_abi_target')
#
# This is here rather than in the toolchain files because it's used
# also by //build/rust/std to find the Rust standard library.
#
# The list of architectures supported by Rust is here:
# https://doc.rust-lang.org/nightly/rustc/platform-support.html
# Although most of these are not yet supported by our limited
# official Rust toolchain (see 'toolchain_has_official_rust' above)
# it's useful to be able to experiment with our other platforms,
# so we try to be comprehensive here.
#
# It's OK if rust_abi_target is blank. That means we're building for the host
# and the host stdlib will be used.
rust_abi_target = ""
if (is_android) {
  import("//build/config/android/abi.gni")
  rust_abi_target = android_abi_target
  if (rust_abi_target == "arm-linux-androideabi") {
    # Android clang target specifications mostly match Rust, but this
    # is an exception
    rust_abi_target = "armv7-linux-androideabi"
  }
} else if (is_fuchsia) {
  if (target_cpu == "arm64") {
    rust_abi_target = "aarch64-fuchsia"
  } else if (target_cpu == "x64") {
    rust_abi_target = "x86_64-fuchsia"
  } else {
    assert(false, "Architecture not supported")
  }
} else if (is_ios) {
  if (target_cpu == "arm64") {
    rust_abi_target = "aarch64-apple-ios"
  } else if (target_cpu == "arm") {
    # There's also an armv7s-apple-ios, which targets a more recent ARMv7
    # generation CPU found in later iPhones. We'll go with the older one for
    # maximal compatibility. As we come to support all the different platforms
    # with Rust, we might want to be more precise here.
    rust_abi_target = "armv7-apple-ios"
  } else if (target_cpu == "x64") {
    rust_abi_target = "x86_64-apple-ios"
  } else if (target_cpu == "x86") {
    rust_abi_target = "i386-apple-ios"
  } else {
    assert(false, "Architecture not supported")
  }
}

# Arguments for Rust invocation.
# This is common between gcc/clang, Mac and Windows toolchains so specify once,
# here. This is not the complete command-line: toolchains should add -o
# and probably --emit arguments too.
rustc_common_args = "--crate-name {{crate_name}} {{source}} --crate-type {{crate_type}} {{rustflags}} {{rustdeps}} {{externs}}"