Fix build on Python 3.14 + GCC 15 by isolating internal C headers

[jerome-benoit]

Python 3.14 introduces C++ templates in dynamic_annotations.h (included via internal/pycore_interp.h). This caused compilation errors ("template with C linkage") because these headers were included inside extern "C" blocks in c_trace_callbacks.h, which is required for Cython/C++ compatibility.

This commit refactors the code to separate the interface from the implementation details:

• Moved internal Python header includes and compatibility macros (for _PyGC_FINALIZED, HAVE_STD_ATOMIC, etc.) from c_trace_callbacks.h to c_trace_callbacks.c.
• c_trace_callbacks.c is now compiled asFix build on Python 3.14 by isolating internal C headers

Python 3.14 introduces C++ templates in dynamic_annotations.h (included via internal/pycore_interp.h). This caused compilation errors ("template with C linkage") because these headers were included inside extern "C" blocks in c_trace_callbacks.h, which is required for Cython/C++ compatibility.

This commit refactors the code to separate the interface from the implementation details:

• Moved internal Python header includes and compatibility macros (for _PyGC_FINALIZED, HAVE_STD_ATOMIC, etc.) from c_trace_callbacks.h to c_trace_callbacks.c.
• c_trace_callbacks.c is now compiled as

[Copilot]

Pull request overview

This PR fixes Python 3.14 build compatibility by refactoring how internal Python headers are included. Python 3.14 introduced C++ templates in dynamic_annotations.h, which caused "template with C linkage" compilation errors when these headers were included inside extern "C" blocks.

Key changes:

• Moved internal Python header includes (pycore_interp.h) and compatibility macros from the header file to the implementation file
• Added extern "C" guards to the header file for C++ compatibility
• Changed Cython to correctly import from the header file instead of the implementation file

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
line_profiler/c_trace_callbacks.h	Removed internal Python headers and compatibility macros; added extern "C" guards for C++ compatibility
line_profiler/c_trace_callbacks.c	Added internal Python headers and compatibility macros previously in the header file
line_profiler/_line_profiler.pyx	Changed Cython import from .c to .h file (correct best practice)

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[jerome-benoit]

@Erotemic: I have no clue on why the wheel build is failing on windows, it's a simple code move with trivial c++ guard additions to comply with cpython API changes. No functional changes.

Without a similar fix, line_profiler cannot be installed on recent distro including python 3.14 as default: fedora 43, ...

[Erotemic]

Hmm, looks like the issue is real though. I'm not sure exactly what it is either.

[lysnikolaou]

Hey folks! I'm currently trying to figure out what it would take for line_profiler to support the free-threaded build of Python 3.14. This problem is blocking me. Could I help move this along?

The CI failure appears to be related to symbol visibility of a couple of inline functions. Moving these function from the .c file to the header file and defining them with static inline ought to fix the issue, I think.

[Erotemic]

@lysnikolaou if you want to fork this and submit a PR with your modifications to test them on CI that would help. I have limited ability to look into the issues at the moment, but I'll review code if the dashboards are green.

[lysnikolaou]

Sure, I can do that. I didn't want to step on any toes and open a PR before @jerome-benoit has signaled whether they're planning to move this forward.