When building from scratch on Windows I get this warning:

c:\program files (x86)\windows kits\10\include\10.0.17763.0\um\winbase.h(103): warning C4005: 'Yield': macro redefinition [C:\Users\gvanrossum\cpython\PCbuild\pythoncore.vcxproj]

I know there is at least one place where we try to prevent this warning, e.g. in Include/internal/pycore_ast.h there's this line:

#undef Yield   /* undefine macro conflicting with <winbase.h> */

But apparently this isn't enough, or the error comes from a different file, or some rearrangement of header files made this #undef ineffective.

Victor, is it possible that your https://github.com/python/cpython/pull/24933 reintroduced this warning?

Steve, what can I do to diagnose this better? (The warning doesn't tell me where winbase.h was included.)

This issue should be fixed:

commit d36d6a9c1808e87628ebaa855d4bec80130189f4
Author: Victor Stinner <vstinner@python.org>
Date:   Wed Apr 7 13:01:09 2021 +0200

    bpo-43244: Remove Yield macro from pycore_ast.h (GH-25243)
    
    * pycore_ast.h no longer defines the Yield macro.
    * Fix a compiler warning on Windows: "warning C4005: 'Yield': macro
      redefinition".
    * Python-ast.c now defines directly functions with their real
      _Py_xxx() name, rather than xxx().
    * Remove "#undef Yield" in C files including pycore_ast.h.

Fixing this super annoying Yield warning was one of my motivation for moving Python-ast.h to the internal C API (pycore_ast.h) :-D I disliked that Python-ast.h defined tons of symbols without "Py" (or "_Py") prefix:

commit 94faa0724f8cbae6867c491c8e465e35f4fdbfbb
Author: Victor Stinner <vstinner@python.org>
Date:   Tue Mar 23 20:47:40 2021 +0100

    bpo-43244: Remove ast.h, asdl.h, Python-ast.h headers (GH-24933)
    
    These functions were undocumented and excluded from the limited C
    API.
    
    Most names defined by these header files were not prefixed by "Py"
    and so could create names conflicts. For example, Python-ast.h
    defined a "Yield" macro which was conflict with the "Yield" name used
    by the Windows <winbase.h> header.
    
    Use the Python ast module instead.
    
    * Move Include/asdl.h to Include/internal/pycore_asdl.h.
    * Move Include/Python-ast.h to Include/internal/pycore_ast.h.
    * Remove ast.h header file.
    * pycore_symtable.h no longer includes Python-ast.h.

Thanks! Dup of bpo-43244.