pw_build/python_script.gni

# Copyright 2019 The Pigweed Authors
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may not
# use this file except in compliance with the License. You may obtain a copy of
# the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations under
# the License.

# Defines an action to run a Python script.
#
# This wraps a regular Python script action with an invocation of a script-
# runner script which resolves GN paths to filesystem paths and locates output
# files for binary targets.
#
# The interface to this template is identical to that of a regular "action"
# which runs a Python script, except for two key differences:
#
#   1. Regular GN actions typically require a call to rebase_path to resolve
#      GN paths to filesystem paths. This template requires that all paths
#      remain GN paths, but are made absolute.
#
#      This means that an "action" argument of the form:
#
#        rebase_path("my/relative/path:optional_target", root_build_dir)
#
#      Becomes:
#
#        get_path_info("my/relative/path:optional_target", "abspath")
#
#   2. The behavior of the runner script depends on whether a provided path is a
#      regular build path or an output path (starting with "$root_out_dir").
#      If an output path is provided and the path has a target, the script
#      assumes that the target refers to a file built by Ninja and tries to
#      locate it within the output directory.
#
# Additionally, this template can accept a boolean "stamp" argument. If set to
# true, the script runner will touch a file to indicate the success of the run.
# This is provided so that individual Python scripts are not required to define
# an output file if they do not have one.
#
# Path resolution examples (assuming the build directory is //out):
#
#           BEFORE                     AFTER
#
#   //my_module              ../my_module
#   //my_module:foo          ../my_module:foo
#   //my_module/file.txt     ../my_module/file.txt
#   $root_out_dir/my_module  ../out/obj/my_module
#   $target_out_dir          ../out/obj/my_module      (in //my_module/BUILD.gn)
#   $target_out_dir/out.json ../out/obj/my_module/out.json
#   $target_out_dir:foo      ../out/obj/my_module/foo.elf  (toolchain-dependent)
#   $target_out_dir:foo      ../out/obj/my_module/foo.exe  (toolchain-dependent)
#
template("pw_python_script") {
  assert(defined(invoker.script), "pw_python_script requires a script to run")

  _script_args = [
    # GN root directory relative to the build directory (in which the runner
    # script is invoked).
    "--gn-root",
    rebase_path("//", root_build_dir),

    # Output directory root, used to determine whether to search for a binary.
    "--out-dir",
    root_out_dir,
  ]

  if (defined(invoker.inputs)) {
    _inputs = invoker.inputs
  } else {
    _inputs = []
  }

  # List the script to run as an input so that the action is re-run when it is
  # modified.
  _inputs += [ invoker.script ]

  if (defined(invoker.outputs)) {
    _outputs = invoker.outputs
  } else {
    _outputs = []
  }

  # If a stamp file is requested, add it as an output of the runner script.
  if (defined(invoker.stamp) && invoker.stamp) {
    _stamp_file = "$target_gen_dir/$target_name.pw_pystamp"
    _outputs += [ _stamp_file ]
    _script_args += [
      "--touch",
      _stamp_file,
    ]
  }

  # "--" indicates the end of arguments to the runner script.
  # Everything beyond this point is interpreted as the command and arguments
  # of the Python script to run.
  _script_args += [ "--" ]

  _script_args += [ get_path_info(invoker.script, "abspath") ]
  if (defined(invoker.args)) {
    _script_args += invoker.args
  }

  action(target_name) {
    _ignore_vars = [
      "script",
      "args",
      "inputs",
      "outputs",
    ]
    forward_variables_from(invoker, "*", _ignore_vars)

    script = "$dir_pw_build/py/python_runner.py"
    args = _script_args
    inputs = _inputs
    outputs = _outputs
  }
}