Use empty structs instead of empty enums for opaque types.

Empty enums are uninhabited types and can cause issues like rust-lang/rust#74840

This fixes the compiler warning: static of uninhabited type

Author: dgrunwald

python27-sys/src/dictobject.rs

@@ -3,7 +3,7 @@ use libc::{c_char, c_int};
 use crate::object::*;
 use crate::pyport::Py_ssize_t;
 
-//pub enum PyDictObject { /* representation hidden */ }
+//#[repr(C)] pub struct PyDictObject { /* representation hidden */ }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
 extern "C" {

python27-sys/src/longobject.rs

@@ -3,7 +3,7 @@ use libc::{c_char, c_double, c_int, c_long, c_longlong, c_ulong, c_ulonglong, c_
 use crate::object::*;
 use crate::pyport::Py_ssize_t;
 
-//enum PyLongObject { /* representation hidden */ }
+//#[repr(C)] struct PyLongObject { /* representation hidden */ }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
 extern "C" {

python27-sys/src/pyarena.rs

@@ -3,7 +3,7 @@ use libc::{c_int, c_void, size_t};
 use crate::object::PyObject;
 
 #[allow(missing_copy_implementations)]
-pub enum PyArena {}
+#[repr(C)] pub struct PyArena { _private: [u8; 0] }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
 extern "C" {

python27-sys/src/pystate.rs

@@ -3,7 +3,7 @@ use libc::{c_int, c_long};
 use crate::frameobject::PyFrameObject;
 use crate::object::PyObject;
 
-pub enum PyInterpreterState {}
+#[repr(C)] pub struct PyInterpreterState { _private: [u8; 0] }
 
 pub type Py_tracefunc = unsafe extern "C" fn(
     arg1: *mut PyObject,

python27-sys/src/pythonrun.rs

@@ -22,11 +22,13 @@ pub struct PyCompilerFlags {
 }
 
 #[allow(missing_copy_implementations)]
-pub enum Struct__mod {}
+#[repr(C)] pub struct Struct__mod { _private: [u8; 0] }
+
 #[allow(missing_copy_implementations)]
-pub enum Struct__node {}
+#[repr(C)] pub struct Struct__node { _private: [u8; 0] }
+
 #[allow(missing_copy_implementations)]
-pub enum Struct_symtable {}
+#[repr(C)] pub struct Struct_symtable { _private: [u8; 0] }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
 extern "C" {

python27-sys/src/setobject.rs

@@ -3,7 +3,7 @@ use libc::c_int;
 use crate::object::*;
 use crate::pyport::Py_ssize_t;
 
-//enum PySetObject { /* representation hidden */ }
+//#[repr(C)] pub struct PySetObject { _private: [u8; 0] }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
 extern "C" {

python3-sys/src/code.rs

@@ -5,7 +5,8 @@ use crate::object::*;
 use crate::pyport::Py_ssize_t;
 
 #[cfg(Py_3_8)]
-pub enum _PyOpcache {}
+#[repr(C)]
+pub struct _PyOpcache { _private: [u8; 0] }
 
 #[repr(C)]
 #[derive(Copy)]

python3-sys/src/frameobject.rs

@@ -14,7 +14,8 @@ pub struct PyTryBlock {
 }
 
 #[cfg(Py_LIMITED_API)]
-pub enum PyFrameObject {}
+#[repr(C)]
+pub struct PyFrameObject { _private: [u8; 0] }
 
 #[cfg(not(Py_LIMITED_API))]
 #[repr(C)]

python3-sys/src/longobject.rs

@@ -3,7 +3,8 @@ use libc::{c_char, c_double, c_int, c_long, c_longlong, c_ulong, c_ulonglong, c_
 use crate::object::*;
 use crate::pyport::Py_ssize_t;
 
-pub enum PyLongObject {}
+#[repr(C)]
+pub struct PyLongObject { _private: [u8; 0] }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
 extern "C" {

python3-sys/src/object.rs

@@ -201,7 +201,8 @@ pub type vectorcallfunc = unsafe extern "C" fn(
 ) -> *mut crate::object::PyObject;
 
 #[cfg(Py_LIMITED_API)]
-pub enum PyTypeObject {}
+#[repr(C)]
+pub struct PyTypeObject { _private: [u8; 0] }
 
 #[cfg(not(Py_LIMITED_API))]
 mod typeobject {

python3-sys/src/pyarena.rs

@@ -1 +1,2 @@
-pub enum PyArena {}
+#[repr(C)]
+pub struct PyArena { _private: [u8; 0] }

python3-sys/src/pystate.rs

@@ -8,8 +8,11 @@ use crate::object::PyObject;
 #[cfg(Py_3_6)]
 pub const MAX_CO_EXTRA_USERS: libc::c_int = 255;
 
-pub enum PyInterpreterState {}
-pub enum PyThreadState {}
+#[repr(C)]
+pub struct PyInterpreterState { _private: [u8; 0] }
+
+#[repr(C)]
+pub struct PyThreadState { _private: [u8; 0] }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
 extern "C" {

python3-sys/src/pythonrun.rs

@@ -37,7 +37,9 @@ pub struct PyCompilerFlags {
 }
 
 #[cfg(not(Py_LIMITED_API))]
-pub enum _mod {}
+#[repr(C)]
+pub struct _mod { _private: [u8; 0] }
+
 
 #[cfg(not(Py_LIMITED_API))]
 #[cfg_attr(windows, link(name = "pythonXY"))]
@@ -116,8 +118,11 @@ extern "C" {
     ) -> *mut _mod;
 }
 
-pub enum symtable {}
-pub enum _node {}
+#[repr(C)]
+pub struct symtable { _private: [u8; 0] }
+
+#[repr(C)]
+pub struct _node { _private: [u8; 0] }
 
 #[inline]
 #[deprecated(since = "0.5.2", note = "Deprecated since Python 3.9")]

python3-sys/src/weakrefobject.rs

@@ -2,7 +2,8 @@ use libc::c_int;
 
 use crate::object::*;
 
-pub enum PyWeakReference {}
+#[repr(C)]
+pub struct PyWeakReference { _private: [u8; 0] }
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
 extern "C" {