bpo-43868: Remove PyOS_ReadlineFunctionPointer from the stable ABI list (GH-25442)

The inclusion of PyOS_ReadlineFunctionPointer in python3dll.c was a mistake.

According to PEP 384:
> functions expecting FILE* are not part of the ABI, to avoid depending
> on a specific version of the Microsoft C runtime DLL on Windows.

https://bugs.python.org/issue43868

Author: encukou

Doc/whatsnew/3.10.rst

@@ -1740,6 +1740,12 @@ Removed
   Use Python :mod:`symtable` module instead.
   (Contributed by Victor Stinner in :issue:`43244`.)
 
+* Remove :c:func:`PyOS_ReadlineFunctionPointer` from the limited C API headers
+  and from ``python3.dll``, the library that provides the stable ABI on
+  Windows. Since the function takes a ``FILE*`` argument, its ABI stability
+  cannot be guaranteed.
+  (Contributed by Petr Viktorin in :issue:`43868`.)
+
 * Remove ``ast.h``, ``asdl.h``, and ``Python-ast.h`` header files.
   These functions were undocumented and excluded from the limited C API.
   Most names defined by these header files were not prefixed by ``Py`` and so

Include/cpython/pythonrun.h

@@ -118,3 +118,4 @@ PyAPI_FUNC(PyObject *) PyRun_FileFlags(FILE *fp, const char *p, int s, PyObject
 /* Stuff with no proper home (yet) */
 PyAPI_FUNC(char *) PyOS_Readline(FILE *, FILE *, const char *);
 PyAPI_DATA(PyThreadState*) _PyOS_ReadlineTState;
+PyAPI_DATA(char) *(*PyOS_ReadlineFunctionPointer)(FILE *, FILE *, const char *);

Include/pythonrun.h

@@ -16,7 +16,6 @@ PyAPI_FUNC(void) PyErr_Display(PyObject *, PyObject *, PyObject *);
 
 /* Stuff with no proper home (yet) */
 PyAPI_DATA(int) (*PyOS_InputHook)(void);
-PyAPI_DATA(char) *(*PyOS_ReadlineFunctionPointer)(FILE *, FILE *, const char *);
 
 /* Stack size, in "pointers" (so we get extra safety margins
    on 64-bit platforms).  On a 32-bit platform, this translates

Misc/NEWS.d/next/C API/2021-04-16-18-15-56.bpo-43868.twQ7KH.rst

@@ -0,0 +1,3 @@
+:c:func:`PyOS_ReadlineFunctionPointer` is no longer exported by limited C API
+headers and by ``python3.dll`` on Windows. Like any function that takes
+``FILE*``, it is not part of the stable ABI.

PC/python3dll.c

@@ -808,7 +808,6 @@ EXPORT_DATA(PyODictIter_Type)
 EXPORT_DATA(PyODictKeys_Type)
 EXPORT_DATA(PyODictValues_Type)
 EXPORT_DATA(PyOS_InputHook)
-EXPORT_DATA(PyOS_ReadlineFunctionPointer)
 EXPORT_DATA(PyProperty_Type)
 EXPORT_DATA(PyRange_Type)
 EXPORT_DATA(PyRangeIter_Type)