Make fields of initialization config public and implement Default

The structs added in dgrunwald#211 did not have public fields. The
fields need to be public in order to allow modifying them.

Furthermore, instantiating new instances of these structs would
be cumbersome (even with public fields) because there are so
many fields. So, we implement Default to construct new instances
that are zero initialized.

python3-sys/src/initconfig.rs

@@ -14,10 +14,23 @@ pub enum PyStatusType {
 #[repr(C)]
 #[derive(Copy, Clone)]
 pub struct PyStatus {
-    _type: PyStatusType,
-    func: *const c_char,
-    err_msg: *const c_char,
-    exitcode: c_int,
+    pub _type: PyStatusType,
+    pub func: *const c_char,
+    pub err_msg: *const c_char,
+    pub exitcode: c_int,
+}
+
+impl Default for PyStatus {
+    fn default() -> Self {
+        // zeroed() is UB for enums. So we are explicit about
+        // what value it is set to. This probably isn't necessary
+        // as we are dealing with a C-compat struct and 0 is a valid
+        // enum value. But explicit is better than UB.
+        let mut status: Self = unsafe { core::mem::zeroed() };
+        status._type = PyStatusType::_PyStatus_TYPE_OK;
+
+        status
+    }
 }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
@@ -35,8 +48,8 @@ extern "C" {
 #[repr(C)]
 #[derive(Copy, Clone)]
 pub struct PyWideStringList {
-    length: Py_ssize_t,
-    items: *mut *mut wchar_t,
+    pub length: Py_ssize_t,
+    pub items: *mut *mut wchar_t,
 }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
@@ -52,18 +65,24 @@ extern "C" {
 #[repr(C)]
 #[derive(Clone)]
 pub struct PyPreConfig {
-    _config_init: c_int,
-    parse_argv: c_int,
-    isolated: c_int,
-    use_environment: c_int,
-    configure_locale: c_int,
-    coerce_c_locale: c_int,
-    coerce_c_locale_warn: c_int,
+    pub _config_init: c_int,
+    pub parse_argv: c_int,
+    pub isolated: c_int,
+    pub use_environment: c_int,
+    pub configure_locale: c_int,
+    pub coerce_c_locale: c_int,
+    pub coerce_c_locale_warn: c_int,
     #[cfg(windows)]
-    legacy_windows_fs_encoding: c_int,
-    utf8_mode: c_int,
-    dev_mode: c_int,
-    allocator: c_int,
+    pub legacy_windows_fs_encoding: c_int,
+    pub utf8_mode: c_int,
+    pub dev_mode: c_int,
+    pub allocator: c_int,
+}
+
+impl Default for PyPreConfig {
+    fn default() -> Self {
+        unsafe { core::mem::zeroed() }
+    }
 }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
@@ -75,62 +94,68 @@ extern "C" {
 #[repr(C)]
 #[derive(Clone)]
 pub struct PyConfig {
-    _config_init: c_int,
-    isolated: c_int,
-    use_environment: c_int,
-    dev_mode: c_int,
-    install_signal_handlers: c_int,
-    use_hash_seed: c_int,
-    hash_seed: c_ulong,
-    faulthandler: c_int,
-    tracemalloc: c_int,
-    import_time: c_int,
-    show_ref_count: c_int,
-    show_alloc_count: c_int,
-    dump_refs: c_int,
-    malloc_stats: c_int,
-    filesystem_encoding: *mut wchar_t,
-    filesystem_errors: *mut wchar_t,
-    pycache_prefix: *mut wchar_t,
-    parse_argv: c_int,
-    argv: PyWideStringList,
-    program_name: *mut wchar_t,
-    xoptions: PyWideStringList,
-    warnoptions: PyWideStringList,
-    site_import: c_int,
-    bytes_warning: c_int,
-    inspect: c_int,
-    interactive: c_int,
-    optimization_level: c_int,
-    parser_debug: c_int,
-    write_bytecode: c_int,
-    verbose: c_int,
-    quiet: c_int,
-    user_site_directory: c_int,
-    configure_c_stdio: c_int,
-    buffered_stdio: c_int,
-    stdio_encoding: *mut wchar_t,
-    stdio_errors: *mut wchar_t,
+    pub _config_init: c_int,
+    pub isolated: c_int,
+    pub use_environment: c_int,
+    pub dev_mode: c_int,
+    pub install_signal_handlers: c_int,
+    pub use_hash_seed: c_int,
+    pub hash_seed: c_ulong,
+    pub faulthandler: c_int,
+    pub tracemalloc: c_int,
+    pub import_time: c_int,
+    pub show_ref_count: c_int,
+    pub show_alloc_count: c_int,
+    pub dump_refs: c_int,
+    pub malloc_stats: c_int,
+    pub filesystem_encoding: *mut wchar_t,
+    pub filesystem_errors: *mut wchar_t,
+    pub pycache_prefix: *mut wchar_t,
+    pub parse_argv: c_int,
+    pub argv: PyWideStringList,
+    pub program_name: *mut wchar_t,
+    pub xoptions: PyWideStringList,
+    pub warnoptions: PyWideStringList,
+    pub site_import: c_int,
+    pub bytes_warning: c_int,
+    pub inspect: c_int,
+    pub interactive: c_int,
+    pub optimization_level: c_int,
+    pub parser_debug: c_int,
+    pub write_bytecode: c_int,
+    pub verbose: c_int,
+    pub quiet: c_int,
+    pub user_site_directory: c_int,
+    pub configure_c_stdio: c_int,
+    pub buffered_stdio: c_int,
+    pub stdio_encoding: *mut wchar_t,
+    pub stdio_errors: *mut wchar_t,
     #[cfg(windows)]
-    legacy_windows_stdio: c_int,
-    check_hash_pycs_mode: *mut wchar_t,
-    pathconfig_warnings: c_int,
-    pythonpath_env: *mut wchar_t,
-    home: *mut wchar_t,
-    module_search_paths_set: c_int,
-    module_search_paths: PyWideStringList,
-    executable: *mut wchar_t,
-    base_executable: *mut wchar_t,
-    prefix: *mut wchar_t,
-    base_prefix: *mut wchar_t,
-    exec_prefix: *mut wchar_t,
-    base_exec_prefix: *mut wchar_t,
-    skip_source_first_line: c_int,
-    run_command: *mut wchar_t,
-    run_module: *mut wchar_t,
-    run_filename: *mut wchar_t,
-    _install_importlib: c_int,
-    _init_main: c_int,
+    pub legacy_windows_stdio: c_int,
+    pub check_hash_pycs_mode: *mut wchar_t,
+    pub pathconfig_warnings: c_int,
+    pub pythonpath_env: *mut wchar_t,
+    pub home: *mut wchar_t,
+    pub module_search_paths_set: c_int,
+    pub module_search_paths: PyWideStringList,
+    pub executable: *mut wchar_t,
+    pub base_executable: *mut wchar_t,
+    pub prefix: *mut wchar_t,
+    pub base_prefix: *mut wchar_t,
+    pub exec_prefix: *mut wchar_t,
+    pub base_exec_prefix: *mut wchar_t,
+    pub skip_source_first_line: c_int,
+    pub run_command: *mut wchar_t,
+    pub run_module: *mut wchar_t,
+    pub run_filename: *mut wchar_t,
+    pub _install_importlib: c_int,
+    pub _init_main: c_int,
+}
+
+impl Default for PyConfig {
+    fn default() -> Self {
+        unsafe { core::mem::zeroed() }
+    }
 }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]