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, 25 insertions, 0 deletions

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index f3ed77e5162..c0323763f44 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -1209,6 +1209,31 @@ init_interp_main(PyThreadState *tstate)
         }
     }
 
+    if (!is_main_interp) {
+        // The main interpreter is handled in Py_Main(), for now.
+        if (config->sys_path_0 != NULL) {
+            PyObject *path0 = PyUnicode_FromWideChar(config->sys_path_0, -1);
+            if (path0 == NULL) {
+                return _PyStatus_ERR("can't initialize sys.path[0]");
+            }
+            PyObject *sysdict = interp->sysdict;
+            if (sysdict == NULL) {
+                Py_DECREF(path0);
+                return _PyStatus_ERR("can't initialize sys.path[0]");
+            }
+            PyObject *sys_path = PyDict_GetItemWithError(sysdict, &_Py_ID(path));
+            if (sys_path == NULL) {
+                Py_DECREF(path0);
+                return _PyStatus_ERR("can't initialize sys.path[0]");
+            }
+            int res = PyList_Insert(sys_path, 0, path0);
+            Py_DECREF(path0);
+            if (res) {
+                return _PyStatus_ERR("can't initialize sys.path[0]");
+            }
+        }
+    }
+
     assert(!_PyErr_Occurred(tstate));
 
     return _PyStatus_OK();