bpo-36763: Add _Py_InitializeMain() (GH-13362)

* Add a private _Py_InitializeMain() function.
* Add again _PyCoreConfig._init_main.
* _Py_InitializeFromConfig() now uses _init_main to decide
  if _Py_InitializeMainInterpreter() should be called.
* _PyCoreConfig: rename _frozen to pathconfig_warnings, its value is
  now the opposite of Py_FrozenFlag.
* Add an unit test for _init_main=0 and _Py_InitializeMain().

2 files changed, 10 insertions, 4 deletions

diff --git a/Include/cpython/coreconfig.h b/Include/cpython/coreconfig.h
index a04342e..c2c5566 100644
--- a/Include/cpython/coreconfig.h
+++ b/Include/cpython/coreconfig.h
@@ -398,10 +398,14 @@ typedef struct {
        See PEP 552 "Deterministic pycs" for more details. */
     wchar_t *check_hash_pycs_mode;
 
-    /* If greater than 0, suppress _PyPathConfig_Calculate() warnings.
+    /* If greater than 0, suppress _PyPathConfig_Calculate() warnings on Unix.
+       The parameter has no effect on Windows.
 
-       If set to -1 (default), inherit Py_FrozenFlag value. */
-    int _frozen;
+       If set to -1 (default), inherit !Py_FrozenFlag value. */
+    int pathconfig_warnings;
+
+    /* If equal to 0, stop Python initialization before the "main" phase */
+    int _init_main;
 
 } _PyCoreConfig;
 
@@ -438,7 +442,8 @@ typedef struct {
         .buffered_stdio = -1, \
         ._install_importlib = 1, \
         .check_hash_pycs_mode = NULL, \
-        ._frozen = -1}
+        .pathconfig_warnings = -1, \
+        ._init_main = 1}
 /* Note: _PyCoreConfig_INIT sets other fields to 0/NULL */
 
 #ifdef __cplusplus
diff --git a/Include/cpython/pylifecycle.h b/Include/cpython/pylifecycle.h
index 2366c77..a3ab6c9 100644
--- a/Include/cpython/pylifecycle.h
+++ b/Include/cpython/pylifecycle.h
@@ -40,6 +40,7 @@ PyAPI_FUNC(_PyInitError) _Py_InitializeFromWideArgs(
     const _PyCoreConfig *config,
     int argc,
     wchar_t **argv);
+PyAPI_FUNC(_PyInitError) _Py_InitializeMain(void);
 
 PyAPI_FUNC(int) _Py_RunMain(void);