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Include/cpython/pyarena.h declares 4 functions which are implemented in Python/pyarena.c. The header file exists to access these functions from the compiler. IMO there was no intent to expose these functions to the public Python C API.
Moreover, the PEP 384 explicitly excludes this API from the stable ABI (from the limited C API).
I propose to move these functions to the internal C API.
Since these functions are no even documented, I don't think that a deprecation period is needed.
Note: The PR 24550 moved Include/pyarena.h to Include/cpython/pyarena.h.

New changeset b4536e1c6abe4c6219177a89e16575d05ea22f64 by Victor Stinner in branch 'master':
bpo-43244: Rename pycore_ast.h to pycore_ast_state.h (GH-24907)
https://github.com/python/cpython/commit/b4536e1c6abe4c6219177a89e16575d05ea22f64

New changeset 526fdeb2278b61653df704d7cfcaedde504dee48 by Victor Stinner in branch 'master':
bpo-43244: Add pycore_ast.h header file (GH-24908)
https://github.com/python/cpython/commit/526fdeb2278b61653df704d7cfcaedde504dee48

New changeset e0bf70d08c4a4a68782702e747e6bf7670667591 by Victor Stinner in branch 'master':
bpo-43244: Fix test_peg_generator for PyAST_Validate() (GH-24912)
https://github.com/python/cpython/commit/e0bf70d08c4a4a68782702e747e6bf7670667591

New changeset 6af528b4ab342805534c0bfe61d84ed7bb519468 by Victor Stinner in branch 'master':
bpo-43244: Fix test_peg_generators on Windows (GH-24913)
https://github.com/python/cpython/commit/6af528b4ab342805534c0bfe61d84ed7bb519468

New changeset eec8e61992fb654d4cf58de4d727c18622b8303e by Victor Stinner in branch 'master':
bpo-43244: Remove the PyAST_Validate() function (GH-24911)
https://github.com/python/cpython/commit/eec8e61992fb654d4cf58de4d727c18622b8303e

The work on this issue started in Python 3.9 with bpo-21120 which excluded Python-ast.h, ast.h and asdl.h from the limited C API: commit 421a72af4deaec96a49a79951b9c2546a2faa13d.

New changeset 28ad12f8fe889a741661eb99daacebd9243cc1ba by Victor Stinner in branch 'master':
bpo-43244: Remove symtable.h header file (GH-24910)
https://github.com/python/cpython/commit/28ad12f8fe889a741661eb99daacebd9243cc1ba

New changeset 94faa0724f8cbae6867c491c8e465e35f4fdbfbb by Victor Stinner in branch 'master':
bpo-43244: Remove ast.h, asdl.h, Python-ast.h headers (GH-24933)
https://github.com/python/cpython/commit/94faa0724f8cbae6867c491c8e465e35f4fdbfbb

New changeset a81fca6ec8e0f748f8eafa12fb12cf9e12df465c by Victor Stinner in branch 'master':
bpo-43244: Add pycore_compile.h header file (GH-25000)
https://github.com/python/cpython/commit/a81fca6ec8e0f748f8eafa12fb12cf9e12df465c

New changeset 57364ce34e0492fbc8b0a6b8c882f384bb489457 by Victor Stinner in branch 'master':
bpo-43244: Remove parser_interface.h header file (GH-25001)
https://github.com/python/cpython/commit/57364ce34e0492fbc8b0a6b8c882f384bb489457

New changeset 8370e07e1e5b626e78ddc7aadbfaf248976c4454 by Victor Stinner in branch 'master':
bpo-43244: Remove the pyarena.h header (GH-25007)
https://github.com/python/cpython/commit/8370e07e1e5b626e78ddc7aadbfaf248976c4454

Ok, the whole C API related to parser, compiler, AST, ASDL and PyArena moved to the internal C API. So we will have more freedom to evolve it!

In short, this issue is a follow-up of bpo-40939.
These C API removal are related to the final step of the PEP 617 "New PEG parser for CPython": removal of the PyParser C API.
* The PyParser C API produced "node*" objects, like PyParser_SimpleParseFile(FILE*) => node*. This C API was removed in Python 3.10: bpo-40939 "Remove the old parser".
* The AST C API takes "node*" as input: PyAST_FromNode(node*) => mod_ty. I removed these APIs.
* symtable takes "mod_ty" as input.
* ASDL and PyArena API were only useful for the removed AST C APIs.
I searched for removed functions in the top PyPI 4000 projects, there is a single project on 4000: typed_ast. This typed_ast project is special, it copies directly code from CPython. Even after the C API removed, typed_ast can continue to use the internal C API, it only has to define the Py_BUILD_CORE_MODULE macro.

New changeset d36d6a9c1808e87628ebaa855d4bec80130189f4 by Victor Stinner in branch 'master':
bpo-43244: Remove Yield macro from pycore_ast.h (GH-25243)
https://github.com/python/cpython/commit/d36d6a9c1808e87628ebaa855d4bec80130189f4

typed-ast was updated for these changes and to avoid including explicitly pydebug.h (it's included by Python.h: see bpo-35134 change): https://github.com/python/typed_ast/pull/158 

New changeset d27f8d2e07d31670af469ef387a37bc9e96ea8ad by Victor Stinner in branch 'master':
bpo-43244: Rename pycore_ast.h functions to _PyAST_xxx() (GH-25252)
https://github.com/python/cpython/commit/d27f8d2e07d31670af469ef387a37bc9e96ea8ad

"Remove Yield macro from pycore_ast.h"
I'm happy that this one is gone, it was a common and annoying compiler warning on Windows!

I marked bpo-35197 as a duplicate of this issue.