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fix: support Python 3.13 PyConfig layout #1335

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fix: support Python 3.13 PyConfig layout #1335

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68 changes: 48 additions & 20 deletions eden/scm/lib/commands/cmdpy/src/python.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -134,18 +134,40 @@ pub fn py_initialize(args: &[String], sapling_home: Option<&String>) {

check_status!(ffi::Py_PreInitialize(&pre_config), None);

let mut config = ffi::PyConfig::default();
// python3-sys 0.7.2 is missing fields added in Python 3.13 (cpu_count,
// sys_path_0), making the Rust PyConfig struct ~12 bytes too small.
// PyConfig_InitPythonConfig writes the full C struct, so we need extra
// space to prevent a buffer overflow. The overflow_guard absorbs this.
//
// The missing cpu_count field also shifts the C offsets of all later
// fields (executable, prefix, module_search_paths, etc.) relative to
// the Rust struct. We avoid accessing any shifted field directly:
// - executable: computed automatically by PyConfig_Read
// - module_search_paths: only set for Python 3.10
// - prefix: only set for static_libpython builds
// Fields we DO set (install_signal_handlers, site_import, parse_argv,
// user_site_directory, argv) all precede cpu_count and are unaffected.
#[repr(C, align(8))]
struct PyConfigStorage {
inner: ffi::PyConfig,
_overflow_guard: [u64; 8],
}
let mut storage = PyConfigStorage {
inner: ffi::PyConfig::default(),
_overflow_guard: [0u64; 8],
};
let config = (&mut storage as *mut PyConfigStorage).cast::<ffi::PyConfig>();

// Ideally we could use PyConfig_InitIsolatedConfig, but we rely on some
// of the vanilla initialization logic to find the std lib, at least.
ffi::PyConfig_InitPythonConfig(&mut config);
ffi::PyConfig_InitPythonConfig(config);

config.install_signal_handlers = 0;
config.site_import = 0;
config.parse_argv = 0;
(*config).install_signal_handlers = 0;
(*config).site_import = 0;
(*config).parse_argv = 0;

// This allows IPython to be installed in user site dir.
config.user_site_directory = 1;
(*config).user_site_directory = 1;

// This assumes Python has been pre-initialized, and filesystem encoding
// is utf-8 (both done above).
Expand All @@ -156,15 +178,15 @@ pub fn py_initialize(args: &[String], sapling_home: Option<&String>) {
}
}

check_status!(
ffi::PyConfig_SetString(&mut config, &mut config.executable, to_wide(&args[0])),
Some(config)
);

// Note: we intentionally skip setting config.executable here. On
// Python < 3.13 it was set to args[0] (current_exe), but PyConfig_Read
// computes it automatically. On Python >= 3.13, the field offset is
// wrong in python3-sys 0.7.2 due to the missing cpu_count field.
// argv is before cpu_count in the struct layout, so it's safe.
for arg in args.iter() {
check_status!(
ffi::PyWideStringList_Append(&mut config.argv, to_wide(arg)),
Some(config)
ffi::PyWideStringList_Append(&mut (*config).argv, to_wide(arg)),
None
);
}
Comment on lines 186 to 191

Expand All @@ -178,13 +200,19 @@ pub fn py_initialize(args: &[String], sapling_home: Option<&String>) {
let exe_dir = exe_dir.to_str().expect("utf-8 exe dir");
// "prefix" affects many other paths.
// See https://docs.python.org/3/c-api/init_config.html#init-path-config
//
// WARNING: On Python 3.13+, config.prefix has the wrong Rust offset
// due to the missing cpu_count field in python3-sys 0.7.2. This code
// path (static_libpython) is not used on standard OSS builds, so this

@quark-zju quark-zju Jun 11, 2026

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This is not true, though. The manylinux build does use static libpython.

// is acceptable for now. A proper fix requires vendoring python3-sys
// or migrating to PyO3.
check_status!(
ffi::PyConfig_SetString(&mut config, &mut config.prefix, to_wide(exe_dir)),
Some(config)
None
);
Comment on lines +203 to 212
}

check_status!(ffi::PyConfig_Read(&mut config), Some(config));
check_status!(ffi::PyConfig_Read(config), None);

// "3.10.9 (v3.10.9:1dd9be6584, Dec 6 2022, 14:37:36) [Clang 13.0.0 (clang-1300.0.29.30)]"
let version = CStr::from_ptr(ffi::Py_GetVersion());
Expand All @@ -203,10 +231,10 @@ pub fn py_initialize(args: &[String], sapling_home: Option<&String>) {
if minor_version == Some(10) {
if let Some(home) = sapling_home {
// This tells Py_Main to not overwrite sys.path and to copy our below value.
config.module_search_paths_set = 1;
(*config).module_search_paths_set = 1;
check_status!(
ffi::PyWideStringList_Append(&mut config.module_search_paths, to_wide(home)),
Some(config)
ffi::PyWideStringList_Append(&mut (*config).module_search_paths, to_wide(home)),
None
);
}
}
Expand All @@ -217,9 +245,9 @@ pub fn py_initialize(args: &[String], sapling_home: Option<&String>) {
ffi::PyImport_FrozenModules = EXTRA_FROZEN_MODULES.0.as_ptr() as _;
}

check_status!(ffi::Py_InitializeFromConfig(&config), Some(config));
check_status!(ffi::Py_InitializeFromConfig(config), None);

ffi::PyConfig_Clear(&mut config);
ffi::PyConfig_Clear(config);
}
}

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