gh-109853: Fix sys.path[0] For Subinterpreters (gh-109994)

This change makes sure sys.path[0] is set properly for subinterpreters. Before, it wasn't getting set at all. This PR does not address the broader concerns from gh-109853.

1 files changed, 28 insertions, 10 deletions

diff --git a/Modules/main.c b/Modules/main.c
index 05bedff..8184bed 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -556,6 +556,11 @@ pymain_run_python(int *exitcode)
         goto error;
     }
 
+    // XXX Calculate config->sys_path_0 in getpath.py.
+    // The tricky part is that we can't check the path importers yet
+    // at that point.
+    assert(config->sys_path_0 == NULL);
+
     if (config->run_filename != NULL) {
         /* If filename is a package (ex: directory or ZIP file) which contains
            __main__.py, main_importer_path is set to filename and will be
@@ -571,24 +576,37 @@ pymain_run_python(int *exitcode)
     // import readline and rlcompleter before script dir is added to sys.path
     pymain_import_readline(config);
 
+    PyObject *path0 = NULL;
     if (main_importer_path != NULL) {
-        if (pymain_sys_path_add_path0(interp, main_importer_path) < 0) {
-            goto error;
-        }
+        path0 = Py_NewRef(main_importer_path);
     }
     else if (!config->safe_path) {
-        PyObject *path0 = NULL;
         int res = _PyPathConfig_ComputeSysPath0(&config->argv, &path0);
         if (res < 0) {
             goto error;
         }
-
-        if (res > 0) {
-            if (pymain_sys_path_add_path0(interp, path0) < 0) {
-                Py_DECREF(path0);
-                goto error;
-            }
+        else if (res == 0) {
+            Py_CLEAR(path0);
+        }
+    }
+    // XXX Apply config->sys_path_0 in init_interp_main().  We have
+    // to be sure to get readline/rlcompleter imported at the correct time.
+    if (path0 != NULL) {
+        wchar_t *wstr = PyUnicode_AsWideCharString(path0, NULL);
+        if (wstr == NULL) {
             Py_DECREF(path0);
+            goto error;
+        }
+        config->sys_path_0 = _PyMem_RawWcsdup(wstr);
+        PyMem_Free(wstr);
+        if (config->sys_path_0 == NULL) {
+            Py_DECREF(path0);
+            goto error;
+        }
+        int res = pymain_sys_path_add_path0(interp, path0);
+        Py_DECREF(path0);
+        if (res < 0) {
+            goto error;
         }
     }