clang warns "warning: redefinition of typedef 'PyTypeObject' is a C11 feature [-Wtypedef-redefinition]"

[colesbury]

BPO	39571
Nosy	@vstinner, @colesbury
PRs	bpo-39571: Fix clang warning on PyTypeObject typedef #18385

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-02-07.00:49:45.257>
created_at = <Date 2020-02-06.17:09:38.996>
labels = ['expert-C-API', '3.9']
title = 'clang warns "warning: redefinition of typedef \'PyTypeObject\' is a C11 feature [-Wtypedef-redefinition]"'
updated_at = <Date 2020-02-07.00:49:45.256>
user = 'https://github.com/colesbury'

bugs.python.org fields:

activity = <Date 2020-02-07.00:49:45.256>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2020-02-07.00:49:45.257>
closer = 'vstinner'
components = ['C API']
creation = <Date 2020-02-06.17:09:38.996>
creator = 'colesbury'
dependencies = []
files = []
hgrepos = []
issue_num = 39571
keywords = ['patch']
message_count = 7.0
messages = ['361497', '361506', '361507', '361509', '361512', '361520', '361521']
nosy_count = 2.0
nosy_names = ['vstinner', 'colesbury']
pr_nums = ['18385']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue39571'
versions = ['Python 3.9']

[colesbury]

A recent commit added a typedef for PyTypeObject in Include/object.h

0e4e735

This duplicates the typedef in Include/cpython/object.h. Building with clang now issues a warning:

./Include/cpython/object.h:274:3: warning: redefinition of typedef 'PyTypeObject' is a C11 feature [-Wtypedef-redefinition]

This is due to the combination of -Wall and -std=c99. GCC will only warn if the -pedantic option is specified.

[vstinner]

Sorry, I only tested GCC and I forgot that clang is more pedantic on duplicated typedef. I looked better with PyTypeObject, but the fix is easy: just revert my change: PR 18384.

[colesbury]

Alternatively I think you can just remove the typedef from Include/cpython/object.h since Include/object.h is always included first. i.e.:

typedef struct _typeobject {
  ...
} PyTypeObject;

to simply

struct _typeobject {
  ...
};

[vstinner]

Alternatively I think you can just remove the typedef from Include/cpython/object.h since Include/object.h is always included first. i.e.:

Oh, nice! I proposed PR 18385. Would you mind to confirm that it fix the issue for you? At least, I tested manually and the clang warning goes away with this change.

[colesbury]

Yes, that fixes the warnings for me. Thanks!

[vstinner]

New changeset f95cd19 by Victor Stinner in branch 'master':
bpo-39571: Fix clang warning on PyTypeObject typedef (GH-18385)
f95cd19

[vstinner]

Thanks Sam Gross for the hint, it's now fixed.