# Copyright 2020 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.

import("//build/fuzzing/fuzzer.gni")
import("//build/rust/rustc_staticlib.gni")

# Defines a Rust fuzzer
#
# The template creates a Rust static library with fuzz target functions enabled
# and provides it to the usual `fuzzer` template. This can create three
# different outputs based on the toolchain variant applied to the target:
#
#   - If the toolchain variant is "rust-*san-fuzzer", this will build a fuzzer
#     which instruments the Rust code of the target and its dependencies.
#
#   - If the toolchain variant is "*san-fuzzer", this will build a fuzzer which
#     instruments the C/C++ code of the target and its dependencies.
#
#   - Otherwise, it will build an uninstrumented unit test that ensures the
#     fuzzer code can build and link.
#
# Parameters:
#
#   rustfunction (optional)
#     Name of the fuzz target function. Defaults to the GN target name.
#     See also https://llvm.org/docs/LibFuzzer.html#fuzz-target.
#
#   version
#   edition
#   configs
#   data_deps
#   deps
#   source_root
#   enforce_source_listing
#   sources
#   inputs
#   features
#   rustenv
#   disable_rbe
#     Same meaning as for rustc_staticlib.
#
#   cmx
#   dictionary
#   options
#   executable parameters, except deps
#     Same meaning as for fuzzer.
#
# Example:
#
# In src/lib.rs:
#   fuzz!("my_fuzzer", (input: ArbitraryType), { ... });
#
# In BUILD.gn:
#   rust_fuzzer("my_fuzzer") {}
#
template("rustc_fuzzer") {
  fuzzer_name = target_name
  fuzzer_lib = "${fuzzer_name}_lib"
  fuzzer_cfg = "${fuzzer_name}_cfg"

  rustfunction = target_name
  if (defined(invoker.rustfunction)) {
    rustfunction = invoker.rustfunction
  }

  if (defined(invoker.original_target_name)) {
    _original_target_name = invoker.original_target_name
  } else {
    _original_target_name = target_name
  }

  config(fuzzer_cfg) {
    visibility = [ ":*" ]
    rustflags = [
      "--cfg=fuzz",
      "--cfg=fuzz_target=\"$rustfunction\"",
    ]

    # fxbug.dev/94239: rustc multiple codegen units seems incompatible
    # with fuzzing.
    configs = [ "//build/config/rust:one_codegen_unit" ]
  }

  rustc_staticlib(fuzzer_lib) {
    forward_variables_from(invoker,
                           [
                             "version",
                             "edition",
                             "source_root",
                             "enforce_source_listing",
                             "sources",
                             "inputs",
                             "features",
                             "rustenv",
                           ])
    visibility = [ ":*" ]
    testonly = true
    configs = []
    configs += invoker.configs
    configs += [ ":$fuzzer_cfg" ]
    deps = [
      "//src/lib/fuzzing/rust:fuzz",
      "//third_party/rust_crates:arbitrary",
    ]
    if (defined(invoker.deps)) {
      deps += invoker.deps
    }
    original_target_name = _original_target_name
  }

  fuzzer(fuzzer_name) {
    non_rust_deps = []
    forward_variables_from(invoker,
                           "*",
                           [
                             "version",
                             "edition",
                             "deps",
                             "source_root",
                             "sources",
                             "inputs",
                             "features",
                             "configs",
                           ])
    deps = [ ":$fuzzer_lib" ]
    deps += non_rust_deps

    # fxbug.dev/94239: rustc multiple codegen units seems incompatible
    # with fuzzing.
    configs += [ "//build/config/rust:one_codegen_unit" ]
  }
}

set_defaults("rustc_fuzzer") {
  configs = default_common_binary_configs + default_rust_configs
}