bpo-43244: Remove the pyarena.h header (GH-25007)

Remove the pyarena.h header file with functions:

* PyArena_New()
* PyArena_Free()
* PyArena_Malloc()
* PyArena_AddPyObject()

These functions were undocumented, excluded from the limited C API,
and were only used internally by the compiler.

Add pycore_pyarena.h header. Rename functions:

* PyArena_New() => _PyArena_New()
* PyArena_Free() => _PyArena_Free()
* PyArena_Malloc() => _PyArena_Malloc()
* PyArena_AddPyObject() => _PyArena_AddPyObject()

3 files changed, 71 insertions, 4 deletions

diff --git a/Include/internal/pycore_asdl.h b/Include/internal/pycore_asdl.h
index 4df0e34..c0b07c3 100644
--- a/Include/internal/pycore_asdl.h
+++ b/Include/internal/pycore_asdl.h
@@ -8,6 +8,8 @@ extern "C" {
 #  error "this header requires Py_BUILD_CORE define"
 #endif
 
+#include "pycore_pyarena.h"       // _PyArena_Malloc()
+
 typedef PyObject * identifier;
 typedef PyObject * string;
 typedef PyObject * object;
@@ -65,7 +67,7 @@ asdl_ ## NAME ## _seq *_Py_asdl_ ## NAME ## _seq_new(Py_ssize_t size, PyArena *a
         return NULL; \
     } \
     n += sizeof(asdl_ ## NAME ## _seq); \
-    seq = (asdl_ ## NAME ## _seq *)PyArena_Malloc(arena, n); \
+    seq = (asdl_ ## NAME ## _seq *)_PyArena_Malloc(arena, n); \
     if (!seq) { \
         PyErr_NoMemory(); \
         return NULL; \
diff --git a/Include/internal/pycore_compile.h b/Include/internal/pycore_compile.h
index f6caec3..e8859bb 100644
--- a/Include/internal/pycore_compile.h
+++ b/Include/internal/pycore_compile.h
@@ -8,7 +8,8 @@ extern "C" {
 #  error "this header requires Py_BUILD_CORE define"
 #endif
 
-struct _mod;   // Type defined in pycore_ast.h
+struct _arena;   // Type defined in pycore_pyarena.h
+struct _mod;     // Type defined in pycore_ast.h
 
 // Export the symbol for test_peg_generator (built as a library)
 PyAPI_FUNC(PyCodeObject*) _PyAST_Compile(
@@ -16,7 +17,7 @@ PyAPI_FUNC(PyCodeObject*) _PyAST_Compile(
     PyObject *filename,
     PyCompilerFlags *flags,
     int optimize,
-    PyArena *arena);
+    struct _arena *arena);
 extern PyFutureFeatures* _PyFuture_FromAST(
     struct _mod * mod,
     PyObject *filename
@@ -31,7 +32,7 @@ typedef struct {
 
 extern int _PyAST_Optimize(
     struct _mod *,
-    PyArena *arena,
+    struct _arena *arena,
     _PyASTOptimizeState *state);
 
 #ifdef __cplusplus
diff --git a/Include/internal/pycore_pyarena.h b/Include/internal/pycore_pyarena.h
new file mode 100644
index 0000000..d78972a
--- /dev/null
+++ b/Include/internal/pycore_pyarena.h
@@ -0,0 +1,64 @@
+/* An arena-like memory interface for the compiler.
+ */
+
+#ifndef Py_INTERNAL_PYARENA_H
+#define Py_INTERNAL_PYARENA_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "this header requires Py_BUILD_CORE define"
+#endif
+
+typedef struct _arena PyArena;
+
+/* _PyArena_New() and _PyArena_Free() create a new arena and free it,
+   respectively.  Once an arena has been created, it can be used
+   to allocate memory via _PyArena_Malloc().  Pointers to PyObject can
+   also be registered with the arena via _PyArena_AddPyObject(), and the
+   arena will ensure that the PyObjects stay alive at least until
+   _PyArena_Free() is called.  When an arena is freed, all the memory it
+   allocated is freed, the arena releases internal references to registered
+   PyObject*, and none of its pointers are valid.
+   XXX (tim) What does "none of its pointers are valid" mean?  Does it
+   XXX mean that pointers previously obtained via _PyArena_Malloc() are
+   XXX no longer valid?  (That's clearly true, but not sure that's what
+   XXX the text is trying to say.)
+
+   _PyArena_New() returns an arena pointer.  On error, it
+   returns a negative number and sets an exception.
+   XXX (tim):  Not true.  On error, _PyArena_New() actually returns NULL,
+   XXX and looks like it may or may not set an exception (e.g., if the
+   XXX internal PyList_New(0) returns NULL, _PyArena_New() passes that on
+   XXX and an exception is set; OTOH, if the internal
+   XXX block_new(DEFAULT_BLOCK_SIZE) returns NULL, that's passed on but
+   XXX an exception is not set in that case).
+*/
+PyAPI_FUNC(PyArena*) _PyArena_New(void);
+PyAPI_FUNC(void) _PyArena_Free(PyArena *);
+
+/* Mostly like malloc(), return the address of a block of memory spanning
+ * `size` bytes, or return NULL (without setting an exception) if enough
+ * new memory can't be obtained.  Unlike malloc(0), _PyArena_Malloc() with
+ * size=0 does not guarantee to return a unique pointer (the pointer
+ * returned may equal one or more other pointers obtained from
+ * _PyArena_Malloc()).
+ * Note that pointers obtained via _PyArena_Malloc() must never be passed to
+ * the system free() or realloc(), or to any of Python's similar memory-
+ * management functions.  _PyArena_Malloc()-obtained pointers remain valid
+ * until _PyArena_Free(ar) is called, at which point all pointers obtained
+ * from the arena `ar` become invalid simultaneously.
+ */
+PyAPI_FUNC(void*) _PyArena_Malloc(PyArena *, size_t size);
+
+/* This routine isn't a proper arena allocation routine.  It takes
+ * a PyObject* and records it so that it can be DECREFed when the
+ * arena is freed.
+ */
+PyAPI_FUNC(int) _PyArena_AddPyObject(PyArena *, PyObject *);
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERNAL_PYARENA_H */