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# Copyright 2020 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
# 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.
"""Script that preprocesses a Python command then runs it.
This script evaluates expressions in the Python command's arguments then invokes
the command.
import argparse
from dataclasses import dataclass
import enum
import logging
import os
from pathlib import Path
import re
import shlex
import subprocess
import sys
from typing import Callable, Dict, Iterable, Iterator, List, NamedTuple
from typing import Optional, Tuple
_LOG = logging.getLogger(__name__)
def _parse_args() -> argparse.Namespace:
"""Parses arguments for this script, splitting out the command to run."""
parser = argparse.ArgumentParser(description=__doc__)
help=('Path to the root of the GN tree; '
'value of rebase_path("//", root_build_dir)'))
help='Value of rebase_path(".", root_build_dir)')
help='Value of default_toolchain')
help='Value of current_toolchain')
parser.add_argument('--module', help='Run this module instead of a script')
help='Environment variables to set as NAME=VALUE')
help='File to touch after the command is run',
help='Capture subcommand output; display only on error',
help='Python script with arguments to run',
return parser.parse_args()
class GnPaths(NamedTuple):
"""The set of paths needed to resolve GN paths to filesystem paths."""
root: Path
build: Path
cwd: Path
# Toolchain label or '' if using the default toolchain
toolchain: str
def resolve(self, gn_path: str) -> Path:
"""Resolves a GN path to a filesystem path."""
if gn_path.startswith('//'):
return self.root.joinpath(gn_path.lstrip('/')).resolve()
return self.cwd.joinpath(gn_path).resolve()
def resolve_paths(self, gn_paths: str, sep: str = ';') -> str:
"""Resolves GN paths to filesystem paths in a delimited string."""
return sep.join(
str(self.resolve(path)) for path in gn_paths.split(sep))
class Label:
"""Represents a GN label."""
name: str
dir: Path
relative_dir: Path
toolchain: Optional['Label']
out_dir: Path
gen_dir: Path
def __init__(self, paths: GnPaths, label: str):
# Use this lambda to set attributes on this frozen dataclass.
set_attr = lambda attr, val: object.__setattr__(self, attr, val)
# Handle explicitly-specified toolchains
if label.endswith(')'):
label, toolchain = label[:-1].rsplit('(', 1)
# Prevent infinite recursion for toolchains
toolchain = paths.toolchain if paths.toolchain != label else ''
set_attr('toolchain', Label(paths, toolchain) if toolchain else None)
# Split off the :target, if provided, or use the last part of the path.
directory, name = label.rsplit(':', 1)
except ValueError:
directory, name = label, label.rsplit('/', 1)[-1]
set_attr('name', name)
# Resolve the directory to an absolute path
set_attr('dir', paths.resolve(directory))
set_attr('relative_dir', self.dir.relative_to(paths.root.resolve()))
'out_dir', / self.toolchain_name() / 'obj' / self.relative_dir)
'gen_dir', / self.toolchain_name() / 'gen' / self.relative_dir)
def gn_label(self) -> str:
label = f'//{self.relative_dir.as_posix()}:{}'
return f'{label}({self.toolchain!r})' if self.toolchain else label
def toolchain_name(self) -> str:
return if self.toolchain else ''
def __repr__(self) -> str:
return self.gn_label()
class _Artifact(NamedTuple):
path: Path
variables: Dict[str, str]
# Matches a non-phony build statement.
_GN_NINJA_BUILD_STATEMENT = re.compile(r'^build (.+):[ \n](?!phony\b)')
# Extensions used for compilation artifacts.
_MAIN_ARTIFACTS = '', '.elf', '.a', '.so', '.dylib', '.exe', '.lib', '.dll'
def _get_artifact(entries: List[str]) -> _Artifact:
"""Attempts to resolve which artifact to use if there are multiple.
Selects artifacts based on extension. This will not work if a toolchain
creates multiple compilation artifacts from one command (e.g. .a and .elf).
assert entries, "There should be at least one entry here!"
if len(entries) == 1:
return _Artifact(Path(entries[0]), {})
filtered = [p for p in entries if Path(p).suffix in _MAIN_ARTIFACTS]
if len(filtered) == 1:
return _Artifact(Path(filtered[0]), {})
raise ExpressionError(
f'Expected 1, but found {len(filtered)} artifacts, after filtering for '
f'extensions {", ".join(repr(e) for e in _MAIN_ARTIFACTS)}: {entries}')
def _parse_build_artifacts(fd) -> Iterator[_Artifact]:
"""Partially parses the build statements in a Ninja file."""
lines = iter(fd)
def next_line():
return next(lines)
except StopIteration:
return None
# Serves as the parse state (only two states)
artifact: Optional[_Artifact] = None
line = next_line()
while line is not None:
if artifact:
if line.startswith(' '): # build variable statements are indented
key, value = (a.strip() for a in line.split('=', 1))
artifact.variables[key] = value
line = next_line()
yield artifact
artifact = None
match = _GN_NINJA_BUILD_STATEMENT.match(line)
if match:
artifact = _get_artifact(
line = next_line()
if artifact:
yield artifact
def _search_target_ninja(ninja_file: Path,
target: Label) -> Tuple[Optional[Path], List[Path]]:
"""Parses the main output file and object files from <target>.ninja."""
artifact: Optional[Path] = None
objects: List[Path] = []
_LOG.debug('Parsing target Ninja file %s for %s', ninja_file, target)
with as fd:
for path, variables in _parse_build_artifacts(fd):
# Older GN used .stamp files when there is no build artifact.
if path.suffix == '.stamp':
if variables:
assert not artifact, f'Multiple artifacts for {target}!'
artifact = Path(path)
return artifact, objects
def _search_toolchain_ninja(ninja_file: Path, paths: GnPaths,
target: Label) -> Optional[Path]:
"""Searches the file for outputs from the provided target.
Files created by an action appear in instead of in their own
<target>.ninja. If the specified target has a single output file in, this function returns its path.
_LOG.debug('Searching toolchain Ninja file %s for %s', ninja_file, target)
# Older versions of GN used a .stamp file to signal completion of a target.
stamp_dir = target.out_dir.relative_to(
stamp_tool = f'{target.toolchain_name()}_stamp'
stamp_statement = f'build {stamp_dir}/{}.stamp: {stamp_tool} '
# Newer GN uses a phony Ninja target to signal completion of a target.
phony_dir = Path(target.toolchain_name(), 'phony',
phony_statement = f'build {phony_dir}/{}: phony '
with as fd:
for line in fd:
for statement in (phony_statement, stamp_statement):
if line.startswith(statement):
output_files = line[len(statement):].strip().split()
if len(output_files) == 1:
return Path(output_files[0])
return None
def _search_ninja_files(
paths: GnPaths,
target: Label) -> Tuple[bool, Optional[Path], List[Path]]:
ninja_file = target.out_dir / f'{}.ninja'
if ninja_file.exists():
return (True, *_search_target_ninja(ninja_file, target))
ninja_file = / target.toolchain_name() / ''
if ninja_file.exists():
return True, _search_toolchain_ninja(ninja_file, paths, target), []
return False, None, []
class TargetInfo:
"""Provides information about a target parsed from a .ninja file."""
label: Label
generated: bool # True if the Ninja files for this target were generated.
artifact: Optional[Path]
object_files: Tuple[Path]
def __init__(self, paths: GnPaths, target: str):
object.__setattr__(self, 'label', Label(paths, target))
generated, artifact, objects = _search_ninja_files(paths, self.label)
object.__setattr__(self, 'generated', generated)
object.__setattr__(self, 'artifact', artifact)
object.__setattr__(self, 'object_files', tuple(objects))
def __repr__(self) -> str:
return repr(self.label)
class ExpressionError(Exception):
"""An error occurred while parsing an expression."""
class _ArgAction(enum.Enum):
OMIT = 1
class _Expression:
def __init__(self, match: re.Match, ending: int):
self._match = match
self._ending = ending
def string(self):
return self._match.string
def end(self) -> int:
return self._ending + len(_ENDING)
def contents(self) -> str:
return self.string[self._match.end():self._ending]
def expression(self) -> str:
return self.string[self._match.start():self.end]
_Actions = Iterator[Tuple[_ArgAction, str]]
def _target_file(paths: GnPaths, expr: _Expression) -> _Actions:
target = TargetInfo(paths, expr.contents())
if not target.generated:
raise ExpressionError(f'Target {target} has not been generated by GN!')
if target.artifact is None:
raise ExpressionError(f'Target {target} has no output file!')
yield _ArgAction.APPEND, str(target.artifact)
def _target_file_if_exists(paths: GnPaths, expr: _Expression) -> _Actions:
target = TargetInfo(paths, expr.contents())
if target.generated:
if target.artifact is None:
raise ExpressionError(f'Target {target} has no output file!')
yield _ArgAction.APPEND, str(target.artifact)
yield _ArgAction.OMIT, ''
def _target_objects(paths: GnPaths, expr: _Expression) -> _Actions:
if expr.expression() != expr.string:
raise ExpressionError(
f'The expression "{expr.expression()}" in "{expr.string}" may '
'expand to multiple arguments, so it cannot be used alongside '
'other text or expressions')
target = TargetInfo(paths, expr.contents())
if not target.generated:
raise ExpressionError(f'Target {target} has not been generated by GN!')
for obj in target.object_files:
yield _ArgAction.EMIT_NEW, str(obj)
# TODO(pwbug/347): Replace expressions with native GN features when possible.
_FUNCTIONS: Dict['str', Callable[[GnPaths, _Expression], _Actions]] = {
'TARGET_FILE': _target_file,
'TARGET_FILE_IF_EXISTS': _target_file_if_exists,
'TARGET_OBJECTS': _target_objects,
_START_EXPRESSION = re.compile(fr'<({"|".join(_FUNCTIONS)})\(')
_ENDING = ')>'
def _expand_arguments(paths: GnPaths, string: str) -> _Actions:
pos = 0
for match in _START_EXPRESSION.finditer(string):
if pos != match.start():
yield _ArgAction.APPEND, string[pos:match.start()]
ending = string.find(_ENDING, match.end())
if ending == -1:
raise ExpressionError(f'Parse error: no terminating "{_ENDING}" '
f'was found for "{string[match.start():]}"')
expression = _Expression(match, ending)
yield from _FUNCTIONS[](paths, expression)
pos = expression.end
if pos < len(string):
yield _ArgAction.APPEND, string[pos:]
def expand_expressions(paths: GnPaths, arg: str) -> Iterable[str]:
"""Expands <FUNCTION(...)> expressions; yields zero or more arguments."""
if arg == '':
return ['']
expanded_args: List[List[str]] = [[]]
for action, piece in _expand_arguments(paths, arg):
if action is _ArgAction.OMIT:
return []
if action is _ArgAction.EMIT_NEW:
return (''.join(arg) for arg in expanded_args if arg)
def main(
gn_root: Path,
current_path: Path,
original_cmd: List[str],
default_toolchain: str,
current_toolchain: str,
module: Optional[str],
env: Optional[List[str]],
capture_output: bool,
touch: Optional[Path],
) -> int:
"""Script entry point."""
if not original_cmd or original_cmd[0] != '--':
_LOG.error('%s requires a command to run', sys.argv[0])
return 1
# GN build scripts are executed from the root build directory.
root_build_dir = Path.cwd().resolve()
tool = current_toolchain if current_toolchain != default_toolchain else ''
paths = GnPaths(root=gn_root.resolve(),
command = [sys.executable]
if module is not None:
command += ['-m', module]
run_args: dict = dict()
if env is not None:
environment = os.environ.copy()
environment.update((k, v) for k, v in (a.split('=', 1) for a in env))
run_args['env'] = environment
if capture_output:
# Combine stdout and stderr so that error messages are correctly
# interleaved with the rest of the output.
run_args['stdout'] = subprocess.PIPE
run_args['stderr'] = subprocess.STDOUT
for arg in original_cmd[1:]:
command += expand_expressions(paths, arg)
except ExpressionError as err:
_LOG.error('%s: %s', sys.argv[0], err)
return 1
_LOG.debug('RUN %s', ' '.join(shlex.quote(arg) for arg in command))
completed_process =, **run_args)
if completed_process.returncode != 0:
_LOG.debug('Command failed; exit code: %d',
if capture_output:
elif touch:
# If a stamp file is provided and the command executed successfully,
# touch the stamp file to indicate a successful run of the command.
touch = touch.resolve()
_LOG.debug('TOUCH %s', touch)
# Create the parent directory in case GN / Ninja hasn't created it.
touch.parent.mkdir(parents=True, exist_ok=True)
return completed_process.returncode
if __name__ == '__main__':