# 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/fuchsia_library_fuzzer.gni")
import("//build/fuzzing/host_library_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 are the same as `executable`, plus:
#
#   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.
#
#   test_inputs
#     Same meaning as for `host_library_fuzzer` when building for host, ignored otherwise.
#
# Example:
#
# In src/lib.rs:
#   fuzz!("my_fuzzer", (input: ArbitraryType), { ... });
#
# In BUILD.gn:
#   rustc_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
  }

  staticlib_vars = [
    "deps",
    "version",
    "edition",
    "source_root",
    "enforce_source_listing",
    "sources",
    "inputs",
    "features",
    "rustenv",
  ]

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

    # https://fxbug.dev/42176112: rustc multiple codegen units seems incompatible
    # with fuzzing.
    configs = [ "//build/config/rust:one_codegen_unit" ]
  }

  rustc_staticlib(fuzzer_lib) {
    testonly = true
    visibility = [ ":*" ]
    forward_variables_from(invoker, staticlib_vars)
    configs = []
    configs = [ ":$fuzzer_cfg" ] + invoker.configs
    original_target_name = _original_target_name
    disable_rustdoc = true
  }
  staticlib_vars += [ "configs" ]

  # https://fxbug.dev/42176112: rustc multiple codegen units are incompatible with fuzzing.
  ignored_parameters = []
  if (is_fuchsia) {
    ignored_parameters += [ "test_inputs" ]
    fuchsia_library_fuzzer(target_name) {
      forward_variables_from(invoker, "*", staticlib_vars + ignored_parameters)
      deps = [ ":$fuzzer_lib" ]
      configs += [ "//build/config/rust:one_codegen_unit" ]
    }
  } else {
    # TODO(https://fxbug.dev/42056966): Remove once all fuzzers are using explicit manifests.
    host_library_fuzzer(target_name) {
      forward_variables_from(invoker, "*", staticlib_vars + ignored_parameters)
      deps = [ ":$fuzzer_lib" ]
      configs += [ "//build/config/rust:one_codegen_unit" ]
    }
  }
  not_needed(invoker, ignored_parameters)
}

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