bpo-34725: Adds _Py_SetProgramFullPath so embedders may override sys.executable (GH-9861)

Author: zooba

Include/pylifecycle.h

@@ -44,6 +44,8 @@ PyAPI_FUNC(void) Py_SetPythonHome(const wchar_t *);
 PyAPI_FUNC(wchar_t *) Py_GetPythonHome(void);
 
 #ifndef Py_LIMITED_API
+PyAPI_FUNC(void) _Py_SetProgramFullPath(const wchar_t *);
+
 /* Only used by applications that embed the interpreter and need to
  * override the standard encoding determination mechanism
  */

Misc/NEWS.d/next/C API/2018-10-13-16-30-54.bpo-34725.j52rIS.rst

@@ -0,0 +1 @@
+Adds _Py_SetProgramFullPath so embedders may override sys.executable

Modules/main.c

@@ -1206,6 +1206,25 @@ config_init_program_name(_PyCoreConfig *config)
 }
 
 
+static _PyInitError
+config_init_executable(_PyCoreConfig *config)
+{
+    assert(config->executable == NULL);
+
+    /* If Py_SetProgramFullPath() was called, use its value */
+    const wchar_t *program_full_path = _Py_path_config.program_full_path;
+    if (program_full_path != NULL) {
+        config->executable = _PyMem_RawWcsdup(program_full_path);
+        if (config->executable == NULL) {
+            return _Py_INIT_NO_MEMORY();
+        }
+        return _Py_INIT_OK();
+    }
+
+    return _Py_INIT_OK();
+}
+
+
 static void
 pymain_header(_PyMain *pymain)
 {
@@ -2350,6 +2369,13 @@ _PyCoreConfig_Read(_PyCoreConfig *config)
         }
     }
 
+    if (config->executable == NULL) {
+        err = config_init_executable(config);
+        if (_Py_INIT_FAILED(err)) {
+            return err;
+        }
+    }
+
     if (config->utf8_mode < 0 || config->coerce_c_locale < 0) {
         config_init_locale(config);
     }

Python/pathconfig.c

@@ -205,6 +205,27 @@ Py_SetProgramName(const wchar_t *program_name)
 }
 
 
+void
+_Py_SetProgramFullPath(const wchar_t *program_full_path)
+{
+    if (program_full_path == NULL || program_full_path[0] == L'\0') {
+        return;
+    }
+
+    PyMemAllocatorEx old_alloc;
+    _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
+
+    PyMem_RawFree(_Py_path_config.program_full_path);
+    _Py_path_config.program_full_path = _PyMem_RawWcsdup(program_full_path);
+
+    PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
+
+    if (_Py_path_config.program_full_path == NULL) {
+        Py_FatalError("Py_SetProgramFullPath() failed: out of memory");
+    }
+}
+
+
 wchar_t *
 Py_GetPath(void)
 {