tools/devshell/build

#!/bin/bash
# Copyright 2017 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.

#### CATEGORY=Build
#### PREBUILTS=${PREBUILT_BAZEL} ${PREBUILT_GN} ${PREBUILT_JQ} ${PREBUILT_NINJA} ${PREBUILT_PYTHON3}
### Run Ninja to build Fuchsia

## usage: fx build [options] [LABELS_OR_TARGETS]... [-- EXTRA_OPTIONS...]
##
## Builds a set of targets after performing a few correctness checks for
## the Fuchsia build. Ninja or Bazel specific options must be provided after
## a -- specifier.
##
## There are three ways to build targets with this command:
##
## - The "GN build mode", which is the default, to build GN or Ninja artifacts
##   by specifying their labels or output paths, respectively, and using
##   a few options specific to this mode (e.g. --toolchain=TOOLCHAIN).
##
## - The "Bazel build mode", which is enabled by using Bazel target labels
##   that begin with @ (e.g. @//src:foo), and Bazel-specific options
##   (e.g. "--config=NAME").
##
## - The "Fint build mode", which is enabled by using --fint-params-path=FILE
##   to point to a fint textproto file describing the build configuration.
##   No other GN or Bazel related arguments are allowed in this mode.
##
## Trying to mix Bazel or GN/Ninja related labels or options is not supported
## and an error message will be printed detailing the issue if this happens.
##
## Some options (e.g. --host) can be used in both modes.
##
## If no Bazel labels or option is used, the build mode defaults to GN, which
## is useful to run Ninja tools, e.g. `fx build -- -t <tool> <tool-options>`.
##
## LABELS_OR_TARGETS is a list whose items can be:
##
##  - GN labels (beginning with //, e.g. //src/foo or //src/foo:bar)
##
##  - Ninja output paths (e.g. host_x64/fidlc) though this use is deprecated
##    and will print a warning.
##
##  - Bazel labels (beginning with @, e.g. @//src/foo or @//src/foo:bar)
##
## Currently only host targets in the Bazel graph that do not depend on GN build
## artifacts are supported. For example, one of:
##
##    fx build --host @//build/bazel/rules/host_tests/tests/cc:static_test
##    fx build --config=host @//build/bazel/rules/host_tests/tests/cc:static_test
##    fx build --fuchsia_platform @//build/bazel/rules/host_tests/tests/cc:dynamic_test
##    fx build --config=fuchsia_platform @//build/bazel/rules/host_tests/tests/cc:dynamic_test
##
## Otherwise, LABELS_OR_TARGETS is a list of Ninja target paths, GN labels
## (beginning with //) or `--toolchain=NAME` options or related aliases (see below).
## For example, the following lines are equivalent ways to ask for the host `zbi`
## tool to be built with Ninja:
##
##    fx build --host //zircon/tools/zbi
##    fx build --host //zircon/tools/zbi:zbi
##    fx build --toolchain=//build/toolchain:host_x64 //zircon/tools/zbi
##    fx build '//zircon/tools/zbi(//build/toolchain:host_x64)'
##    fx build host_x64/zbi
##
## The first line above is favored. Using the last line will print a warning
## instructing the user which (optional) toolchain option + label to use instead.
##
## optional arguments:
##   -h, --help               Print this message. Use '-- --help' to print
##                            Ninja-specific help.
##
##   --no-checks              Disable consistency checks (for fx development only).
##
##   --log=LOGFILE
##   --log LOGFILE            Print debug information to LOGFILE. Please attach
##                            the resulting file when reporting bugs.
##
##   --fint-params-path=PATH
##   --fint-params-path PATH  Path to a fint params file used by an infra
##                            builder. This is useful for reproducing the exact
##                            set of targets built by the infrastructure.
##                            All other options listed below are ignored in this mode.
##
##   --toolchain=TOOLCHAIN    Specify the current GN toolchain suffix to use for
##                            GN labels that appear after this option. It is an error
##                            to use this with any Bazel target label or option.
##
##   --config=NAME            Specify a Bazel --config argument. It is an error to use
##                            this with any GN target label or Ninja output path argument.
##
##   -j <count>               Specify an explicit max job count for both Ninja
##                            and Bazel.
##
##   -q, --quiet              Tell Ninja and Bazel to be quiet.
##
##   --no-status              Suppress dynamic terminal output. Use this for
##                            non-interactive shells. Set automatically if an
##                            agentic runtime is detected by ANTIGRAVITY_AGENT,
##                            ANTIGRAVITY_EDITOR_APP_ROOT, or GEMINI_CLI.
##                            Currently only affects the Ninja build system.
##
##   --skip-auth-check        Bypass pre-flight build service authentication
##                            checks.
##
##   --resultstore[=VAL]      Enable uploading build events to ResultStore.
##                            VAL can be 'all', 'ninja', 'bazel', or 'none'.
##                            If VAL is omitted, 'all' is assumed.
##
##   --no-resultstore         Disable uploading build events to ResultStore.
##
##   --verbose                Print extra information, such as the list of
##                            Ninja targets corresponding to the input GN labels
##                            to build. This does *not* enable Ninja --verbose flag,
##                            use '-- --verbose' to do that.
##
##   --experimental-tui       Enable terminal UI for monitoring build.
##
##   --host                   When building with Ninja, an alias for --toolchain=host.
##                            When building with Bazel, an alias for --config=host
##
##   --default                Alias for --toolchain=default
##                            (incompatible with Bazel build mode)
##
##   --fuchsia                Alias for --toolchain=fuchsia
##                            (incompatible with Bazel build mode)
##
##   --fidl                   Alias for --toolchain=fidl
##                            (incompatible with Bazel build mode)
##
##   -- [ARGS...]             Pass all following arguments directly to Ninja or
##                            Bazel.
##
##   --help-toolchains        Print list of valid TOOLCHAIN values.
##
## Run `fx build -- -h` to see Ninja argument details.

declare -r start_time="${EPOCHREALTIME/./}"

# Note: Do not use $(dirname "${BASH_SOURCE[0]}") to locate the script's
# directory to save about 7ms of startup time. See https://fxbug.dev/42085680
# The fallback is only needed when invoking directly with bash as in:
# `(cd tools/devshell && bash build)`
_script_dir="${BASH_SOURCE[0]%/*}"; if [[ "${_script_dir}" == "${BASH_SOURCE[0]}" ]]; then _script_dir=.; fi
# shellcheck source=/dev/null
source "${_script_dir}/lib/vars.sh" || exit 1
# shellcheck source=/dev/null
source "${_script_dir}/lib/build_api_client.sh" || exit $?
fx-config-read
# shellcheck source=/dev/null
source "${_script_dir}/lib/bazel_utils.sh" || exit $?

# shellcheck source=/dev/null
source "${_script_dir}/lib/metrics.sh" || exit $?

shopt -s extglob

function print-toolchain-help {
  cat <<EOF
Possible --toolchain aliases

  host     Host toolchain    (//build/toolchain:host_$HOST_CPU)
  default  Default toolchain (//build/toolchain/fuchsia:\$TARGET_CPU)
  fuchsia  Default toolchain as well.
  fidl     FIDL toolchain    (//build/fidl:fidling)

Apart from that, the --toolchain value must be a valid GN toolchain
label, such as '//some/toolchain:target'.
EOF
}

function get-ninja-log-timestamp {
  NINJA_LOG_FILE="${FUCHSIA_BUILD_DIR}/.ninja_log"
  if [[ -f "${NINJA_LOG_FILE}" ]]; then
    stat -c "%Y" "${NINJA_LOG_FILE}"
  else
    echo -1
  fi
}

# Validate the command-line arguments to determine whether this is used
# to build Bazel targets, or GN / Ninja ones.
#
# On failure, this prints a human-friendly error message detailing the incompatible
# arguments, then return 1
#
# On success, this sets the global FX_BUILD_MODE variable to either "gn", "bazel",
# "fint" or an empty string if the mode could not be determined.
#
# $1+: command-line arguments
function validate_build_args {
  local gn_options=() gn_labels=() bazel_options=() bazel_targets=()
  local gn_args=()   # gn labels and options, in invocation order.
  local has_fint_params_path
  while [[ $# -gt 0 ]]; do
    case "$1" in
      --config=*)  # A Bazel --config=NAME option
        if [[ "${#gn_labels[@]}" -gt 0 ]]; then
          fx-error "Bazel option $1 cannot be used with GN labels or Ninja paths: ${gn_labels[*]}"
          return 1
        elif [[ "${#gn_options[@]}" -gt 0 ]]; then
          fx-error "Bazel option $1 cannot be used with GN/Ninja options: ${gn_options[*]}"
          return 1
        fi
        bazel_options+=("$1")
        ;;
      @*)  # A Bazel target label.
        if [[ "${#gn_labels[@]}" -gt 0 ]]; then
          fx-error "Bazel target $1 cannot be used with GN labels or Ninja paths: ${gn_labels[*]}"
          return 1
        elif [[ "${#gn_options[@]}" -gt 0 ]]; then
          fx-error "Bazel target $1 cannot be used with GN/Ninja options: ${gn_options[*]}"
          return 1
        fi
        bazel_targets+=("$1")
        ;;
      --fuchsia_platform)
        # This is a short-cut for --config=fuchsia_platform
        bazel_options+=("--config=fuchsia_platform")
        ;;
      --host)
        # This is compatible with both Bazel and GN invocations so ignore it here.
        gn_args+=("$1")
        ;;
      --toolchain=*|--fuchsia|--default|--fidl)  # GN specific options.
        if [[ "${#bazel_targets[@]}" -gt 0 ]]; then
          fx-error "GN option $1 cannot be used with Bazel targets: ${bazel_targets[*]}"
          return 1
        fi
        if [[ "${#bazel_options[@]}" -gt 0 ]]; then
          fx-error "GN option $1 cannot be used with Bazel options: ${bazel_options[*]}"
          return 1
        fi
        gn_options+=("$1")
        gn_args+=("$1")
        ;;
      --)  # Stop parsing after the --
        shift
        break
        ;;
      --fint-params-path|--log|-j)  # Options taking an argument
        if [[ -z "$2" ]]; then
          fx-error "Missing $1 argument, see --help."
          return 1
        fi
        if [[ "$1" == "--fint-params-path" ]]; then
          has_fint_params_path=true
        fi
        shift
        ;;
      --fint-params-path=*)
        has_fint_params_path=true
        ;;
      -*)  # Ignore any other option here.
        ;;
      //*) # A GN label
        if [[ "${#bazel_targets[@]}" -gt 0 ]]; then
          fx-error "GN label $1 cannot be used with Bazel targets: ${bazel_targets[*]}"
          return 1
        fi
        if [[ "${#bazel_options[@]}" -gt 0 ]]; then
          fx-error "GN label $1 cannot be used with Bazel options: ${bazel_options[*]}"
          return 1
        fi
        gn_labels+=("$1")
        gn_args+=("$1")
        ;;
      *)  # Assume this is a Ninja path
        if [[ "${#bazel_targets[@]}" -gt 0 ]]; then
          fx-error "Ninja path $1 cannot be used with Bazel targets: ${bazel_targets[*]}"
          return 1
        fi
        if [[ "${#bazel_options[@]}" -gt 0 ]]; then
          fx-error "Ninja path $1 cannot be used with Bazel options: ${bazel_options[*]}"
          return 1
        fi
        gn_labels+=("$1")  # Not really a label, but good enough for validation.
        gn_args+=("$1")
        ;;
    esac
    shift
  done

  if [[ -n "${has_fint_params_path}" ]]; then
    if [[ "${#bazel_targets[@]}" -gt 0 || "${#bazel_options[@]}" -gt 0 || "${#gn_args[@]}" -gt 0 ]]; then
      fx-error "It's invalid to specify Bazel or GN arguments along with --fint-params-path."
      return 1
    elif [[ "$*" ]]; then
      fx-error "It's invalid to specify extra Ninja flags along with --fint-params-path."
      return 1
    fi
    FX_BUILD_MODE="fint"
  elif [[ "${#bazel_targets[@]}" -gt 0 || "${#bazel_options[@]}" -gt 0 ]]; then
    FX_BUILD_MODE="bazel"
  elif [[ "${#gn_labels[@]}" -gt 0 || "${#gn_options[@]}" -gt 0 ]]; then
    FX_BUILD_MODE="gn"
    # A common mistake is to place a toolchain option after the GN label, thinking it
    # applies to all labels. For example `fx build //src:foo --host` instead of
    # `fx build --host //src:foo`.
    #
    # The latter builds //src:foo for the host, but the former builds //src:foo for Fuchsia,
    # then ignores the --host option. This results in confusing build error messages
    # (see https://fxbug.dev/328421720), so detect this here and make trailing toolchain
    # options an error with an explicit message.
    local last_gn_arg="${gn_args[-1]}"
    if [[ "${last_gn_arg}" =~ --.* ]]; then
      fx-error "Toolchain option ${last_gn_arg} must be followed by at least one GN label"
      return 1
    fi
  else
    FX_BUILD_MODE=""
  fi
}

# Abort script with an error if FX_BUILD_MODE is not "bazel"
function assert_build_mode {
  if [[ "$FX_BUILD_MODE" != "$1" ]]; then
    fx-fatal "Internal validation error (expected $1 build mode, got $FX_BUILD_MODE)! Please contact the Fuchsia build team!"
  fi
}

function _array_to_json_list {
  if [[ "${#@}" -eq 0 ]]; then
    printf "[]"
    return 0
  fi
  local item comma
  printf "["
  for item in "${@}"; do
    printf %s "$comma"
    comma=","
    printf '"%q"' "${item}"
  done
  printf "]"
}

function main {
  local gn_targets=() extra_switches=() bazel_targets=() fx_gen_switches=()
  local log_file is_logging fint_params_path
  local no_checks
  local verbose
  local quiet
  local skip_auth_check=0

  if [[ "${FX_BUILD_QUIET}" == "1" ]]; then
    quiet=true
  fi

  # When tracing, increase verbosity.
  if [[ -o xtrace ]]; then
    verbose="true"
  fi

  validate_build_args "$@" || return 1

  # If the build mode could not be determined, set it to "gn" for
  # now, as this is the most common case, and this allows using
  # Ninja tools with invocations like `fx build -- -t deps ninja_target_path`
  # which is very useful to debug weird build issues.
  if [[ -z "$FX_BUILD_MODE" ]]; then
    FX_BUILD_MODE="gn"
  fi

  # As a special case, set FX_BUILD_DEBUG_VALIDATION=1 in the
  # environment to exit the script immediately when validation passed.
  if [[ "${FX_BUILD_DEBUG_VALIDATION}" == "1" ]]; then
    echo "FX_BUILD_MODE ${FX_BUILD_MODE}"
    return 0
  fi

  is_logging=false
  while [[ $# -gt 0 ]]; do
    case "$1" in
      --log=*)
        log_file="${1#--*=}"
        ;;
      --log)
        if [[ $# -lt 2 ]]; then
          fx-error "Missing --log argument, see --help."
          return 1
        fi
        log_file="$2"
        shift
        ;;
      --fint-params-path)
        assert_build_mode "fint"
        fint_params_path="$2"
        shift
        ;;
      --fint-params-path=*)
        assert_build_mode "fint"
        fint_params_path="${1#--*=}"
        ;;
      # Use -- as a separator for command-line options for Ninja.
      # Anything that follows that goes directly into extra_switches and the loop exits.
      --)
        shift
        extra_switches+=("$@")
        break
        ;;

      --no-checks)
        no_checks=true
        ;;

      --no-status)
        # shellcheck disable=SC2034 # Global variable used by tools/devshell/lib/vars.sh
        FX_BUILD_STATUS=0
        ;;

      --skip-auth-check)
        skip_auth_check=1
        ;;

      --resultstore)
        export FX_BUILD_RESULTSTORE_OVERRIDE="all"
        ;;

      --resultstore=*)
        export FX_BUILD_RESULTSTORE_OVERRIDE="${1#--*=}"
        ;;

      --no-resultstore)
        export FX_BUILD_RESULTSTORE_OVERRIDE="none"
        ;;

      --verbose)
        verbose=true
        quiet=
        unset FX_BUILD_QUIET
        ;;

      --experimental-tui)
        TUI_ENABLED=1
        ;;

      -q|--quiet)
        quiet=true
        ;;

      # As a special case, recognize `-j<count>` and `-j <count>` as valid
      # options. For now pass them directly to fx-run-ninja, which will eventually
      # pass them to Bazel. See https://fxbug.dev/351623259
      -j)
        extra_switches+=("$1" "$2")
        shift
        ;;

      -j*)
        extra_switches+=("$1")
        ;;

      -h|--help)
        fx-print-command-help "${BASH_SOURCE[0]}"
        exit 0
        ;;

      --help-toolchains)
        print-toolchain-help
        exit 0
        ;;

      # When building GN targets, --host is an alias for --toolchain=host
      # When building Bazel targets, --host is an alias for --config=host
      --host)
          if [[ "${FX_BUILD_MODE}" == "bazel" ]]; then
            extra_switches+=(--config=host)
          else
            assert_build_mode "gn"
            gn_targets+=("$1")
          fi
          ;;

      --fuchsia_platform)
        assert_build_mode "bazel"
        extra_switches+=("--config=fuchsia_platform")
        ;;

      --config=*)
        assert_build_mode "bazel"
        extra_switches+=("$1")
        ;;

      # The following options are used to specify GN toolchain for future
      # labels that appear on the command line.
      --fidl|--default|--fuchsia|--toolchain=*)
        assert_build_mode "gn"
        gn_targets+=("$1")
        ;;

      -*)
        fx-error "Unsupported option $1, see 'fx help build' for details."
        exit 1
        ;;
      @*)
        assert_build_mode "bazel"
        bazel_targets+=("$1")
        ;;
      *)  # Assume this is a Ninja path.
        assert_build_mode "gn"
        gn_targets+=("$1")
        ;;
    esac
    shift
  done

  if [[ -n "${log_file}" ]]; then
    if [[ -f "${log_file}" ]]; then
      fx-error "File \"${log_file}\" exists. Please delete the file or specify a different path."
      return 1
    fi
    is_logging=true
  fi

  if [[ -n "${quiet}" ]]; then
    fx_gen_switches+=("--quiet")
    case "${FX_BUILD_MODE}" in
      bazel)
        extra_switches+=("--config=quiet")
        ;;
      gn)
        extra_switches+=("--quiet")
        ;;
    esac
    export FX_BUILD_QUIET=1
  fi

  # Set no_checks=true when running a Ninja tool or printing the Ninja help.
  if [[ "${#gn_targets[@]}" -gt 0 ]]; then
    for arg in "${extra_switches[@]}"; do
      case "${arg}" in
        -h|--help|-t*)
          no_checks=true
          break
      esac
    done
  fi

  if [[ "${HOST_OS}" == "mac" ]]; then
    fx-error "Building Fuchsia on macOS is NOT SUPPORTED."
    fx-error "Please see http://go/local-platform-support-prd for details."
    exit 1
  fi

  if [[ "${is_logging}" = true ]]; then
    # log file header with relevant environment information
    {
      TIMESTAMP="$(date +%Y%m%d_%H%M%S)"
      echo "Build initiated at ${TIMESTAMP}"
      echo
      echo "------ GIT QUICK INFO ------"
      echo "$ git status"
      git --no-optional-locks --git-dir="${FUCHSIA_DIR}/.git" status
      echo
      echo "$ git rev-parse JIRI_HEAD"
      git --no-optional-locks --git-dir="${FUCHSIA_DIR}/.git" rev-parse JIRI_HEAD
      echo
      echo "------ CONTENTS OF args.gn ------"
      echo "$ cat ${FUCHSIA_BUILD_DIR}/args.gn"
      echo
      cat "${FUCHSIA_BUILD_DIR}/args.gn"
      echo
    } >> "${log_file}" 2>&1

    # tee stdout and stderr to log_file
    exec > >(tee -a "${log_file}") 2>&1
  fi

  # A list of reasons to run `fx-gen` when needed.
  local need_fx_gen_for=()

  if [[ -z "${no_checks}" ]]; then
    # If a fuchsia-workspace daemon is running, notify it to suspend its build tasks
    # until this `fx build` invocation completes.
    # This prevents the daemon from building concurrently, which slows down
    # local builds by ~40-100%.
    local -r fuchsia_workspace="${_FUCHSIA_WORKSPACE_CLI:-/google/bin/releases/fuchsia-workspace-cli/fuchsia-workspace}"
    if [[ -x "${fuchsia_workspace}" ]]; then
      # This is a best-effort, non-blocking, fire-and-forget request.
      if [[ -n "${verbose}" ]]; then
        timeout 5s "${fuchsia_workspace}" daemon yield "$$" </dev/null &
      else
        timeout 5s "${fuchsia_workspace}" daemon yield "$$" </dev/null >/dev/null 2>&1 &
      fi
    fi

    # A change to any of these might mean things are now done differently enough
    # that ninja's automatic re-gen rule might not be triggered or might not work
    # properly if it is triggered.  So preemptively force a re-gen if that seems
    # like a plausible possibility.

    # LINT.IfChange(landmine_files)
    local -r landmines=("$PREBUILT_GN"
                        "$FUCHSIA_DIR/tools/devshell/build"
                        "$FUCHSIA_DIR/tools/devshell/lib/bazel_utils.sh"
                        "$FUCHSIA_DIR/tools/devshell/lib/vars.sh"
                        "${FUCHSIA_BUILD_DIR}/args.gn"
                      )
    # LINT.ThenChange(//tools/devshell/tests/subcommands/fx_build_test:landmine_files)

    local mine
    for mine in "${landmines[@]}"; do
      if [[ "$mine" -nt "${FUCHSIA_BUILD_DIR}/build.ninja" ]]; then
        need_fx_gen_for+=("$mine changed")
      fi
    done

    if [[ ! -d "$FUCHSIA_BUILD_DIR" ]]; then
      need_fx_gen_for+=("$FUCHSIA_BUILD_DIR missing")
    fi

    # We have a build directory, execute force clean checker, usually a no-op
    local _verbose_opt=()
    if [[ -n "$verbose" ]]; then
      _verbose_opt=(--verbose)
    fi
    local -r force_clean_status_file="$(mktemp --tmpdir force_clean_status.XXXXXX)"
    "$FUCHSIA_DIR/scripts/fuchsia-vendored-python" -S \
      "$FUCHSIA_DIR/build/force_clean/force_clean_if_needed.py" \
      "${_verbose_opt[@]}" \
      --gn-bin "$PREBUILT_GN" \
      --checkout-dir "$FUCHSIA_DIR" \
      --build-dir "$FUCHSIA_BUILD_DIR" \
      --output-status="${force_clean_status_file}" || return "$?"

    local force_clean_status
    force_clean_status="$(< "${force_clean_status_file}")"
    rm "${force_clean_status_file}"

    if [[ "${is_logging}" == true ]]; then
      echo "force_clean status: ${force_clean_status}"
    fi
    case "${force_clean_status}" in
      clean:*)
        need_fx_gen_for+=("${force_clean_status}")
        ;;
    esac

    if [[ "${#need_fx_gen_for[@]}" != 0 ]]; then
      if [[ "${is_logging}" == true ]]; then
        echo -e "\\n------ RUNNING gn gen ------"
      fi
      if [[ "${#need_fx_gen_for[@]}" == 1 ]]; then
        # A single reason goes on a single line.
        echo >&2 "Re-running 'fx gen' first (${need_fx_gen_for[*]})"
      else
        # For multiple reasons, print one per line before the header.
        printf >&2 "Re-running 'fx gen' first:\n\n"
        for reason in "${need_fx_gen_for[@]}"; do
          printf >&2 "  %s\n" "$reason"
        done
      fi
      fx-gen "${fx_gen_switches[@]}" || return "$?"
    fi
  fi

  local status

  if [[ "${is_logging}" == true ]]; then
    echo -e "\\n------ RUNNING ${FX_BUILD_MODE} ------"
  fi

  # A flag indicating whether a Ninja build is needed, as opposed to
  # running a tool, or in dry-run mode.
  local run_ninja_build=
  if [[ "${FX_BUILD_MODE}" == "bazel" ]]; then
    # `fx build --host|--fuchsia_platform <bazel label>` (used by `fx test` to
    # rebuild a single Bazel test) runs `bazel build` directly instead of
    # through a Ninja bazel_action(). Bazel targets can read GN-built artifacts
    # through the @gn_targets repository, which normally points at whatever the
    # last bazel_action() exposed, so pick its contents explicitly here.
    local has_bazel_host_flag has_bazel_fuchsia_platform_flag bazel_arg
    for bazel_arg in "${extra_switches[@]}"; do
      if [[ "${bazel_arg}" == "--config=host" ]]; then
         has_bazel_host_flag=true
      elif [[ "${bazel_arg}" == "--config=fuchsia_platform" ]]; then
         has_bazel_fuchsia_platform_flag=true
      fi
    done

    local gn_targets_dir
    if [[ -n "${has_bazel_host_flag}" ]]; then
      # Bazel host tests don't need any GN artifacts.
      gn_targets_dir="${FUCHSIA_DIR}/build/bazel/local_repositories/empty_gn_targets"
    elif [[ -n "${has_bazel_fuchsia_platform_flag}" ]]; then
      # Expose the @gn_targets inputs declared on //build/bazel/target_tests
      # (cmc and package-tool, needed by fx_package() and fx_test()). This
      # directory is written by `fx gen`, and the tools themselves are built
      # with Ninja below.
      # TODO(https://fxbug.dev/519243783, https://fxbug.dev/519244675): Point at
      # empty_gn_targets once cmc and package-tool are migrated to Bazel.
      # LINT.IfChange(tests_json_gn_targets_dir)
      gn_targets_dir="${FUCHSIA_BUILD_DIR}/build/bazel/tests_json.gn_targets"
      # LINT.ThenChange(//build/bazel/scripts/bazel_tests_utils.py:tests_json_gn_targets_dir)
    else
      fx-error "Only host or fuchsia_platform Bazel target labels are supported for now, please use --host or --fuchsia_platform flag."
      exit 1
    fi
    extra_switches+=(
      # Override @gn_targets (whose Bzlmod canonical repository name is
      # `gn_targets+`) instead of relying on whatever the workspace symlink was
      # last pointed at.
      --override_repository=gn_targets+="${gn_targets_dir}"
    )
  elif [[ "${FX_BUILD_MODE}" == "gn" ]]; then
    run_ninja_build=true
    for opt in "${extra_switches[@]}"; do
      case "${opt}" in
        -n|--dry-run|-t*)
          run_ninja_build=
          ;;
      esac
    done
  fi

  if [[ -n "${run_ninja_build}" ]]; then
    # LINT.IfChange
    # A file that is only created when the build succeeds.
    local last_build_success_stamp="${FUCHSIA_BUILD_DIR}/last_ninja_build_success.stamp"
    # LINT.ThenChange(//tools/integration/fint/build.go)

    rm -f "${last_build_success_stamp}"

    local -i is_no_op=0
    local -i is_clean_build=0
    local -i ninja_log_timestamp_before
    ninja_log_timestamp_before="$(get-ninja-log-timestamp)"
    if (( ninja_log_timestamp_before < 0 )); then
      is_clean_build=1
    fi
  fi

  if [[ "${FX_BUILD_MODE}" == "fint" ]]; then
    (fx-run-build-command "${is_logging}" \
      --fint-params-path "${fint_params_path}" \
      "ninja")
    status=$?
    exit-with-message
  fi

  # When using any remote build services, do a quick authentication
  # check before starting the build.
  if [[ "$skip_auth_check" == 0 ]]; then
    # Return instead of exit to bypass exit-with-message, since RBE
    # authentication failures do not require a build bug report hint.
    fx-command-run rbe preflight
    local -r preflight_status="$?"
    if [[ "${preflight_status}" -ne 0 ]]; then
      fx-error "RBE preflight check failed. If this is an authentication issue, please run: fx rbe auth"
      return "${preflight_status}"
    fi
  fi

  if [[ "${FX_BUILD_MODE}" == "bazel" ]]; then
      fx-update-bazel-workspace

      # --fuchsia_platform requires the sysroot artifacts and the @gn_targets
      # inputs for //build/bazel/target_tests (cmc, package-tool) to be built
      # with Ninja first. For now do this unconditionally. In the future, this
      # will be optimized by a Ninja sub-build invoked on-demand by Bazel
      # itself.
      # TODO(https://fxbug.dev/519243783, https://fxbug.dev/519244675): Drop
      # target_tests.bazel_inputs once cmc and package-tool are migrated to
      # Bazel.
      if [[ "${has_bazel_fuchsia_platform_flag}" ]]; then
        local ninja_path="$PREBUILT_NINJA"
        # The rsninja.sh script is a wrapper that enables ResultStore features,
        # and is a safe drop-in replacement for the original ninja binary,
        # even when ResultStore is disabled.
        if [[ -x "${ninja_path}" ]]; then
          ninja_path="${FUCHSIA_DIR}/build/resultstore/rsninja.sh"
        fi
        fx-run-ninja "${is_logging}" "${ninja_path}" \
          -C "${FUCHSIA_BUILD_DIR}" \
          phony/zircon/public/sysroot_sdk/sysroot_for_fuchsia_platform \
          phony/build/bazel/target_tests/target_tests.bazel_inputs
      fi

      # Invoke Bazel through fx-run-bazel to ensure a consistent environment and RBE wrapper
      # script, compared with the case where Bazel is called from Ninja.
      local bazel_build_args=(
        "${extra_switches[@]}"
        # The target labels or patterns
        "${bazel_targets[@]}"
      )

      (fx-run-bazel "${is_logging}" "$(fx-get-bazel)" build "${bazel_build_args[@]}")
      status=$?

      # Note: for now, these build events are not tracked as this feature is still experimental.
  else
    if [[ "${#gn_targets[@]}" -gt 0 ]]; then
      local -a gn_labels  # define variable to quiet shellcheck
      fx-command-stdout-to-array gn_labels fx-build-api-client fx_build_args_to_labels --allow-targets --args "${gn_targets[@]}" || return "$?"

      # Convert GN labels to Ninja targets now.
      local -a ninja_targets  # define variable to quiet shellcheck
      fx-command-stdout-to-array ninja_targets fx-build-api-client gn_label_to_ninja_paths --allow-unknown "${gn_labels[@]}" || return "$?"

      # For invalid labels, the above command will print errors to stderr directly and not list them in the result.
      # If ninja_targets is empty, we can stop here.
      if [[ -z "${ninja_targets[*]}" ]]; then
        exit 1
      fi

      if [[ -n "${run_ninja_build}" && -n "${verbose}" ]]; then
        echo "Building Ninja target(s): ${ninja_targets[*]}"
      fi
    else
      ninja_targets=("${gn_targets[@]}")
    fi

    if [[ -n "${run_ninja_build}" ]]; then
      # Write the list of Ninja targets to the build directory. See
      # `//build/api/client last_ninja_artifacts` command.
      #
      # Only update the file when its content changes, to avoid the cache
      # created by `//build/api/client` to be regenerated when not needed.
      local ninja_targets_list="${ninja_targets[*]}"
      # LINT.IfChange
      local ninja_targets_list_file="${FUCHSIA_BUILD_DIR}/last_ninja_build_targets.txt"
      # LINT.ThenChange(//tools/integration/fint/build.go)
      if [[ ! -f "${ninja_targets_list_file}" || "$(<"${ninja_targets_list_file}")" != "${ninja_targets_list}" ]]; then
        printf "%s" "${ninja_targets_list}" > "${ninja_targets_list_file}"
      fi
    fi

    local ninja_path="$PREBUILT_NINJA"
    # The rsninja.sh script is a wrapper that enables ResultStore features,
    # and is a safe drop-in replacement for the original ninja binary,
    # even when ResultStore is disabled.
    if [[ -x "${ninja_path}" ]]; then
      ninja_path="${FUCHSIA_DIR}/build/resultstore/rsninja.sh"
    fi

    fx-run-ninja "${is_logging}" "${ninja_path}" \
      -C "${FUCHSIA_BUILD_DIR}" \
      "${extra_switches[@]}" "${ninja_targets[@]}"

    status=$?
    local -i ninja_log_timestamp_after
    ninja_log_timestamp_after="$(get-ninja-log-timestamp)"
    if [[ "${ninja_log_timestamp_before}" == "${ninja_log_timestamp_after}" ]]; then
      is_no_op=1
    fi

    "${PREBUILT_PYTHON3}" "$FUCHSIA_DIR/tools/devshell/contrib/lib/count-ninja-actions.py" --validate-ninja-log-version || exit $?

    if [[ "${status}" == 0 && -n "${run_ninja_build}" ]]; then
      touch "${last_build_success_stamp}"
    fi

    declare -r end_time="${EPOCHREALTIME/./}"
    track-build-event "${start_time}" "${end_time}" "${status}" "${extra_switches[*]}" "${ninja_targets[*]}" "${FUCHSIA_BUILD_DIR}" "${is_no_op}" "${is_clean_build}" "${quiet}"&

  fi
  exit-with-message
}

function exit-with-message {
  if [[ "${is_logging}" = true ]]; then
    fx-warn "Debug log saved to ${log_file}. Please attach this file when reporting a bug"
  elif [[ "${status}" -ne 0 ]]; then
    echo >&2 "Hint: run \`fx build\` with the option \`--log LOGFILE\` to generate a debug log if you are reporting a bug."
  fi
  exit "${status}"
}

main "$@"