bpo-38234: Py_SetPath() uses the program full path (GH-16357)

Py_SetPath() now sets sys.executable to the program full path
(Py_GetProgramFullPath()), rather than to the program name
(Py_GetProgramName()).

Fix also memory leaks in pathconfig_set_from_config().

Doc/c-api/init.rst

@@ -472,8 +472,8 @@ Process-wide parameters
    dependent delimiter character, which is ``':'`` on Unix and Mac OS X, ``';'``
    on Windows.
 
-   This also causes :data:`sys.executable` to be set only to the raw program
-   name (see :c:func:`Py_SetProgramName`) and for :data:`sys.prefix` and
+   This also causes :data:`sys.executable` to be set to the program
+   full path (see :c:func:`Py_GetProgramFullPath`) and for :data:`sys.prefix` and
    :data:`sys.exec_prefix` to be empty.  It is up to the caller to modify these
    if required after calling :c:func:`Py_Initialize`.
 
@@ -483,6 +483,10 @@ Process-wide parameters
    The path argument is copied internally, so the caller may free it after the
    call completes.
 
+   .. versionchanged:: 3.8
+      The program full path is now used for :data:`sys.executable`, instead
+      of the program name.
+
 
 .. c:function:: const char* Py_GetVersion()
 

Doc/whatsnew/3.8.rst

@@ -1347,6 +1347,11 @@ Build and C API Changes
   parameter for indicating the number of positional-only arguments.
   (Contributed by Pablo Galindo in :issue:`37221`.)
 
+* :c:func:`Py_SetPath` now sets :data:`sys.executable` to the program full
+  path (:c:func:`Py_GetProgramFullPath`) rather than to the program name
+  (:c:func:`Py_GetProgramName`).
+  (Contributed by Victor Stinner in :issue:`38234`.)
+
 
 Deprecated
 ==========

Misc/NEWS.d/next/C API/2019-09-24-17-09-48.bpo-38234.d0bhEA.rst

@@ -0,0 +1,3 @@
+:c:func:`Py_SetPath` now sets :data:`sys.executable` to the program full
+path (:c:func:`Py_GetProgramFullPath`) rather than to the program name
+(:c:func:`Py_GetProgramName`).

Python/pathconfig.c

@@ -23,6 +23,7 @@ wchar_t *_Py_dll_path = NULL;
 static int
 copy_wstr(wchar_t **dst, const wchar_t *src)
 {
+    assert(*dst == NULL);
     if (src != NULL) {
         *dst = _PyMem_RawWcsdup(src);
         if (*dst == NULL) {
@@ -172,6 +173,7 @@ pathconfig_set_from_config(_PyPathConfig *pathconfig, const PyConfig *config)
     _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
     if (config->module_search_paths_set) {
+        PyMem_RawFree(pathconfig->module_search_path);
         pathconfig->module_search_path = _PyWideStringList_Join(&config->module_search_paths, DELIM);
         if (pathconfig->module_search_path == NULL) {
             goto no_memory;
@@ -180,6 +182,8 @@ pathconfig_set_from_config(_PyPathConfig *pathconfig, const PyConfig *config)
 
 #define COPY_CONFIG(PATH_ATTR, CONFIG_ATTR) \
         if (config->CONFIG_ATTR) { \
+            PyMem_RawFree(pathconfig->PATH_ATTR); \
+            pathconfig->PATH_ATTR = NULL; \
             if (copy_wstr(&pathconfig->PATH_ATTR, config->CONFIG_ATTR) < 0) { \
                 goto no_memory; \
             } \
@@ -455,16 +459,15 @@ Py_SetPath(const wchar_t *path)
     PyMemAllocatorEx old_alloc;
     _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
-    /* Getting the program name calls pathconfig_global_init() */
-    wchar_t *program_name = _PyMem_RawWcsdup(Py_GetProgramName());
+    /* Getting the program full path calls pathconfig_global_init() */
+    wchar_t *program_full_path = _PyMem_RawWcsdup(Py_GetProgramFullPath());
 
     PyMem_RawFree(_Py_path_config.program_full_path);
     PyMem_RawFree(_Py_path_config.prefix);
     PyMem_RawFree(_Py_path_config.exec_prefix);
     PyMem_RawFree(_Py_path_config.module_search_path);
 
-    /* Copy program_name to program_full_path  */
-    _Py_path_config.program_full_path = program_name;
+    _Py_path_config.program_full_path = program_full_path;
     _Py_path_config.prefix = _PyMem_RawWcsdup(L"");
     _Py_path_config.exec_prefix = _PyMem_RawWcsdup(L"");
     _Py_path_config.module_search_path = _PyMem_RawWcsdup(path);