Hide some API if _Py_OPAQUE_PYOBJECT is defined

API that's removed when _Py_OPAQUE_PYOBJECT is defined:

    - PyObject_HEAD
    - _PyObject_EXTRA_INIT
    - PyObject_HEAD_INIT
    - PyObject_VAR_HEAD
    - struct _object (i.e. PyObject) (opaque)
    - struct PyVarObject (opaque)
    - Py_SIZE
    - Py_SET_TYPE
    - Py_SET_SIZE
    - PyModuleDef_Base (opaque)
    - PyModuleDef_HEAD_INIT
    - PyModuleDef (opaque)
    - _Py_IsImmortal
    - _Py_IsStaticImmortal

Note that the `_Py_IsImmortal` removal means _Py_OPAQUE_PYOBJECT
only works with limited API 3.14+ now.

Author: encukou

Include/moduleobject.h

@@ -36,6 +36,7 @@ PyAPI_FUNC(PyObject *) PyModuleDef_Init(PyModuleDef*);
 PyAPI_DATA(PyTypeObject) PyModuleDef_Type;
 #endif
 
+#ifndef _Py_OPAQUE_PYOBJECT
 typedef struct PyModuleDef_Base {
   PyObject_HEAD
   /* The function used to re-initialize the module.
@@ -63,6 +64,7 @@ typedef struct PyModuleDef_Base {
     0,        /* m_index */      \
     _Py_NULL, /* m_copy */       \
   }
+#endif  // _Py_OPAQUE_PYOBJECT
 
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03050000
 /* New in 3.5 */
@@ -104,6 +106,8 @@ struct PyModuleDef_Slot {
 PyAPI_FUNC(int) PyUnstable_Module_SetGIL(PyObject *module, void *gil);
 #endif
 
+
+#ifndef _Py_OPAQUE_PYOBJECT
 struct PyModuleDef {
   PyModuleDef_Base m_base;
   const char* m_name;
@@ -115,6 +119,7 @@ struct PyModuleDef {
   inquiry m_clear;
   freefunc m_free;
 };
+#endif  // _Py_OPAQUE_PYOBJECT
 
 #ifdef __cplusplus
 }

Include/object.h

@@ -56,6 +56,11 @@ whose size is determined when the object is allocated.
 #  define Py_REF_DEBUG
 #endif
 
+#if defined(_Py_OPAQUE_PYOBJECT) && !defined(Py_LIMITED_API)
+#   error "_Py_OPAQUE_PYOBJECT only makes sense with Py_LIMITED_API"
+#endif
+
+#ifndef _Py_OPAQUE_PYOBJECT
 /* PyObject_HEAD defines the initial segment of every PyObject. */
 #define PyObject_HEAD                   PyObject ob_base;
 
@@ -99,6 +104,8 @@ whose size is determined when the object is allocated.
  * not necessarily a byte count.
  */
 #define PyObject_VAR_HEAD      PyVarObject ob_base;
+#endif // !defined(_Py_OPAQUE_PYOBJECT)
+
 #define Py_INVALID_SIZE (Py_ssize_t)-1
 
 /* PyObjects are given a minimum alignment so that the least significant bits
@@ -112,7 +119,9 @@ whose size is determined when the object is allocated.
  * by hand.  Similarly every pointer to a variable-size Python object can,
  * in addition, be cast to PyVarObject*.
  */
-#ifndef Py_GIL_DISABLED
+#ifdef _Py_OPAQUE_PYOBJECT
+  /* PyObject is opaque */
+#elif !defined(Py_GIL_DISABLED)
 struct _object {
 #if (defined(__GNUC__) || defined(__clang__)) \
         && !(defined __STDC_VERSION__ && __STDC_VERSION__ >= 201112L)
@@ -168,15 +177,18 @@ struct _object {
     Py_ssize_t ob_ref_shared;   // shared (atomic) reference count
     PyTypeObject *ob_type;
 };
-#endif
+#endif // !defined(_Py_OPAQUE_PYOBJECT)
 
 /* Cast argument to PyObject* type. */
 #define _PyObject_CAST(op) _Py_CAST(PyObject*, (op))
 
-typedef struct {
+#ifndef _Py_OPAQUE_PYOBJECT
+struct PyVarObject {
     PyObject ob_base;
     Py_ssize_t ob_size; /* Number of items in variable part */
-} PyVarObject;
+};
+#endif
+typedef struct PyVarObject PyVarObject;
 
 /* Cast argument to PyVarObject* type. */
 #define _PyVarObject_CAST(op) _Py_CAST(PyVarObject*, (op))
@@ -286,6 +298,7 @@ PyAPI_FUNC(PyTypeObject*) Py_TYPE(PyObject *ob);
 PyAPI_DATA(PyTypeObject) PyLong_Type;
 PyAPI_DATA(PyTypeObject) PyBool_Type;
 
+#ifndef _Py_OPAQUE_PYOBJECT
 // bpo-39573: The Py_SET_SIZE() function must be used to set an object size.
 static inline Py_ssize_t Py_SIZE(PyObject *ob) {
     assert(Py_TYPE(ob) != &PyLong_Type);
@@ -295,6 +308,7 @@ static inline Py_ssize_t Py_SIZE(PyObject *ob) {
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
 #  define Py_SIZE(ob) Py_SIZE(_PyObject_CAST(ob))
 #endif
+#endif // !defined(_Py_OPAQUE_PYOBJECT)
 
 static inline int Py_IS_TYPE(PyObject *ob, PyTypeObject *type) {
     return Py_TYPE(ob) == type;
@@ -304,6 +318,7 @@ static inline int Py_IS_TYPE(PyObject *ob, PyTypeObject *type) {
 #endif
 
 
+#ifndef _Py_OPAQUE_PYOBJECT
 static inline void Py_SET_TYPE(PyObject *ob, PyTypeObject *type) {
     ob->ob_type = type;
 }
@@ -323,6 +338,7 @@ static inline void Py_SET_SIZE(PyVarObject *ob, Py_ssize_t size) {
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
 #  define Py_SET_SIZE(ob, size) Py_SET_SIZE(_PyVarObject_CAST(ob), (size))
 #endif
+#endif // !defined(_Py_OPAQUE_PYOBJECT)
 
 
 /*

Include/refcount.h

@@ -117,6 +117,7 @@ PyAPI_FUNC(Py_ssize_t) Py_REFCNT(PyObject *ob);
     #endif
 #endif
 
+#ifndef _Py_OPAQUE_PYOBJECT
 static inline Py_ALWAYS_INLINE int _Py_IsImmortal(PyObject *op)
 {
 #if defined(Py_GIL_DISABLED)
@@ -140,6 +141,7 @@ static inline Py_ALWAYS_INLINE int _Py_IsStaticImmortal(PyObject *op)
 #endif
 }
 #define _Py_IsStaticImmortal(op) _Py_IsStaticImmortal(_PyObject_CAST(op))
+#endif // !defined(_Py_OPAQUE_PYOBJECT)
 
 // Py_SET_REFCNT() implementation for stable ABI
 PyAPI_FUNC(void) _Py_SetRefcnt(PyObject *ob, Py_ssize_t refcnt);