bpo-43795: Don't list private names in the limited API (GH-26740)

* Remove struct _node from the stable ABI list

This struct was removed along with the old parser in Python 3.9 (PEP 617)

* Stable ABI list: Use the public name "PyFrameObject" rather than "_frame"

* Ensure limited API doesn't contain private names

Names prefixed by an underscore are private by definition.

* Add a blurb

Doc/data/stable_abi.dat

@@ -272,6 +272,7 @@ function,PyFloat_GetInfo,3.2,
 function,PyFloat_GetMax,3.2,
 function,PyFloat_GetMin,3.2,
 var,PyFloat_Type,3.2,
+type,PyFrameObject,3.2,
 function,PyFrame_GetCode,3.10,
 function,PyFrame_GetLineNumber,3.10,
 function,PyFrozenSet_New,3.2,
@@ -825,8 +826,6 @@ function,Py_XNewRef,3.10,
 type,Py_intptr_t,3.2,
 type,Py_ssize_t,3.2,
 type,Py_uintptr_t,3.2,
-type,_frame,3.2,
-type,_node,3.2,
 type,allocfunc,3.2,
 type,binaryfunc,3.2,
 type,descrgetfunc,3.2,

Misc/NEWS.d/next/C API/2021-06-15-16-28-18.bpo-43795.fy0AXK.rst

@@ -0,0 +1,3 @@
+The list in :ref:`stable-abi-list` now shows the public name
+:c:struct:`PyFrameObject` rather than ``_frame``. The non-existing
+entry ``_node`` no longer appears in the list.

Misc/stable_abi.txt

@@ -38,12 +38,10 @@ struct PyThreadState
     added 3.2
 struct PyInterpreterState
     added 3.2
-struct _frame
+struct PyFrameObject
     added 3.2
 struct symtable
     added 3.2
-struct _node
-    added 3.2
 struct PyWeakReference
     added 3.2
 struct PyLongObject

Tools/scripts/stable_abi.py

@@ -492,6 +492,16 @@ def gcc_get_limited_api_definitions(headers):
     )
     return stable_data | stable_exported_data | stable_functions
 
+def check_private_names(manifest):
+    """Ensure limited API doesn't contain private names
+
+    Names prefixed by an underscore are private by definition.
+    """
+    for name, item in manifest.contents.items():
+        if name.startswith('_') and not item.abi_only:
+            raise ValueError(
+                f'`{name}` is private (underscore-prefixed) and should be '
+                + 'removed from the stable ABI list or or marked `abi_only`')
 
 def main():
     parser = argparse.ArgumentParser(
@@ -557,6 +567,8 @@ def main():
     with args.file.open() as file:
         manifest = parse_manifest(file)
 
+    check_private_names(manifest)
+
     # Remember results of all actions (as booleans).
     # At the end we'll check that at least one action was run,
     # and also fail if any are false.