Only enable line tracing when building with Cython tracing (#660)

Author: bdraco

CHANGES/660.packaging.rst

@@ -0,0 +1,6 @@
+Fixed an issue where ``frozenlist`` binary wheels would be built with debugging symbols and line tracing enabled, which significantly impacted performance. Line tracing is now disabled by default and can only be enabled explicitly -- by :user:`bdraco`.
+
+This change ensures that production builds are optimized for performance. Developers who need line tracing for debugging purposes can still enable it by:
+
+1. Setting the ``FROZENLIST_CYTHON_TRACING`` environment variable
+2. Using the ``--config-setting=with-cython-tracing=true`` option with pip

packaging/pep517_backend/_backend.py

@@ -291,7 +291,7 @@ def maybe_prebuild_c_extensions(
     with build_dir_ctx:
         config = _get_local_cython_config()
 
-        cythonize_args = _make_cythonize_cli_args_from_config(config)
+        cythonize_args = _make_cythonize_cli_args_from_config(config, cython_line_tracing_requested)
         with _patched_cython_env(config['env'], cython_line_tracing_requested):
             _cythonize_cli_cmd(cythonize_args)
         with patched_distutils_cmd_install():

packaging/pep517_backend/_cython_configuration.py

@@ -17,10 +17,20 @@
 class Config(TypedDict):
     env: dict[str, str]
     flags: dict[str, bool]
-    kwargs: dict[str, str]
+    kwargs: dict[str, str | dict[str, str]]
     src: list[str]
 
 
+def _configure_cython_line_tracing(config_kwargs: dict[str, str | dict[str, str]], cython_line_tracing_requested: bool) -> None:
+    """Configure Cython line tracing directives if requested."""
+    # If line tracing is requested, add it to the directives
+    if cython_line_tracing_requested:
+        directives = config_kwargs.setdefault('directive', {})
+        assert isinstance(directives, dict)  # Type narrowing for mypy
+        directives['linetrace'] = 'True'
+        directives['profile'] = 'True'
+
+
 def get_local_cython_config() -> Config:
     """Grab optional build dependencies from pyproject.toml config.
 
@@ -78,11 +88,15 @@ def get_local_cython_config() -> Config:
     return config_mapping['tool']['local']['cythonize']  # type: ignore[no-any-return]
 
 
-def make_cythonize_cli_args_from_config(config: Config) -> list[str]:
+def make_cythonize_cli_args_from_config(config: Config, cython_line_tracing_requested: bool = False) -> list[str]:
     py_ver_arg = f'-{_python_version_tuple.major!s}'
 
     cli_flags = get_enabled_cli_flags_from_config(config['flags'])
-    cli_kwargs = get_cli_kwargs_from_config(config['kwargs'])
+
+    config_kwargs = config['kwargs']
+    _configure_cython_line_tracing(config_kwargs, cython_line_tracing_requested)
+
+    cli_kwargs = get_cli_kwargs_from_config(config_kwargs)
 
     return cli_flags + [py_ver_arg] + cli_kwargs + ['--'] + config['src']
 

packaging/pep517_backend/_transformers.py

@@ -16,7 +16,9 @@ def _emit_opt_pairs(opt_pair: Tuple[str, Union[str, Dict[str, str]]]) -> Iterato
     yield from ("=".join(map(str, (flag_opt,) + pair)) for pair in sub_pairs)
 
 
-def get_cli_kwargs_from_config(kwargs_map: Mapping[str, str]) -> List[str]:
+def get_cli_kwargs_from_config(
+    kwargs_map: Mapping[str, Union[str, Dict[str, str]]],
+) -> List[str]:
     """Make a list of options with values from config."""
     return list(chain.from_iterable(map(_emit_opt_pairs, kwargs_map.items())))
 

pyproject.toml

@@ -48,7 +48,6 @@ keep-going = false
 # https://cython.rtfd.io/en/latest/src/userguide/source_files_and_compilation.html#compiler-directives
 embedsignature = "True"
 emit_code_comments = "True"
-linetrace = "True"  # Implies `profile=True`
 
 [tool.local.cythonize.kwargs.compile-time-env]
 # This section can contain compile time env vars