Currently, there are *implicit* dependencies between AST/parser header files. For example, ast.h uses node and mod_ty types but don't include node.h nor Python-ast.h. And parsetok.h uses node and grammer but don't include nor grammar.h.

Because of that, C files have to include header files in the "correct order" and need to include header files even if they don't use directly.

At the end, we get something like pythonrun.c:

#include "Python-ast.h"
#include "pycore_state.h"
#include "grammar.h"
#include "node.h"
#include "token.h"
#include "parsetok.h"
#include "errcode.h"
#include "code.h"
#include "symtable.h"
#include "ast.h"
#include "marshal.h"
#include "osdefs.h"
#include <locale.h>

whereas most header files are useless, pythonrun.c still compiles with:

#include "pycore_state.h"
#include "token.h"      /* INDENT in err_input() */
#include "parsetok.h"   /* PyParser_ParseFileObject() */
#include "errcode.h"    /* E_EOF */
#include "symtable.h"   /* PySymtable_BuildObject() */
#include "ast.h"        /* PyAST_FromNodeObject() */
#include "marshal.h"    /* PyMarshal_ReadLongFromFile */
#include <locale.h>

I propose to add explicit dependencies in header files directly, rather than using black magic in C files.

Attached PR fix this issue.

New changeset 5f2df88b63e50d23914e97ec778861a52abdeaad by Victor Stinner in branch 'master':
bpo-35177: Add dependencies between header files (GH-10361)
https://github.com/python/cpython/commit/5f2df88b63e50d23914e97ec778861a52abdeaad

This change doesn't try to fix "all dependencies issues", but it fix a few of them :-) See bpo-35197 for another example of funny header issue.

Please open a new issues if you see other header dependencies issues. I close this one since the initial bug has been fixed.

Oh, the Yield warning made its come back :-( Example:

  import.c
c:\program files (x86)\windows kits\10\include\10.0.17134.0\um\winbase.h(102): warning C4005: 'Yield': macro redefinition [C:\projects\cpython\PCbuild\pythoncore.vcxproj]
  c:\projects\cpython\include\python-ast.h(549): note: see previous definition of 'Yield'

New changeset 3bb183d7fb83ad6a84ec13dea90f95d67be35c69 by Victor Stinner in branch 'master':
bpo-35177, Python-ast.h: Fix "Yield" compiler warning (GH-10664)
https://github.com/python/cpython/commit/3bb183d7fb83ad6a84ec13dea90f95d67be35c69

Ok, I fixed the "Yield warning" again.