gh-127651: Use __file__ in diagnostics if origin is missing

Lib/test/test_import/__init__.py

@@ -815,6 +815,14 @@ def test_frozen_module_from_import_error(self):
             str(cm.exception),
         )
 
+        expected_error = (
+            b"cannot import name 'this_will_never_exist' "
+            b"from 'sys' (unknown location)"
+        )
+        popen = script_helper.spawn_python("-c", "from sys import this_will_never_exist")
+        stdout, stderr = popen.communicate()
+        self.assertIn(expected_error, stdout)
+
 
         scripts = [
             """
@@ -834,11 +842,11 @@ def test_frozen_module_from_import_error(self):
             with self.subTest(script=script):
                 expected_error = (
                     b"cannot import name 'this_will_never_exist' "
-                    b"from 'os' \\(unknown location\\)"
+                    b"from 'os' (unknown location)"
                 )
                 popen = script_helper.spawn_python("-c", script)
                 stdout, stderr = popen.communicate()
-                self.assertRegex(stdout, expected_error)
+                self.assertIn(expected_error, stdout)
 
     def test_script_shadowing_stdlib(self):
         script_errors = [

Python/ceval.c

@@ -2859,6 +2859,20 @@ _PyEval_ImportFrom(PyThreadState *tstate, PyObject *v, PyObject *name)
         }
     }
 
+    if (origin == NULL) {
+        // Fall back to __file__ for diagnostics if we don't have
+        // an origin that is a location
+        origin = PyModule_GetFilenameObject(v);
+        if (origin == NULL) {
+            if (!PyErr_ExceptionMatches(PyExc_SystemError)) {
+                goto done;
+            }
+            // PyModule_GetFilenameObject raised "module filename missing"
+            _PyErr_Clear(tstate);
+        }
+        assert(origin == NULL || PyUnicode_Check(origin));
+    }
+
     if (is_possibly_shadowing_stdlib) {
         assert(origin);
         errmsg = PyUnicode_FromFormat(
@@ -2903,19 +2917,6 @@ _PyEval_ImportFrom(PyThreadState *tstate, PyObject *v, PyObject *name)
         }
         else {
             assert(rc == 0);
-            if (origin == NULL) {
-                // Fall back to __file__ for diagnostics if we don't have
-                // an origin that is a location
-                origin = PyModule_GetFilenameObject(v);
-                if (origin == NULL) {
-                    if (!PyErr_ExceptionMatches(PyExc_SystemError)) {
-                        goto done;
-                    }
-                    // PyModule_GetFilenameObject raised "module filename missing"
-                    _PyErr_Clear(tstate);
-                }
-                assert(origin == NULL || PyUnicode_Check(origin));
-            }
             if (origin) {
                 errmsg = PyUnicode_FromFormat(
                     "cannot import name %R from %R (%S)",
@@ -2932,9 +2933,11 @@ _PyEval_ImportFrom(PyThreadState *tstate, PyObject *v, PyObject *name)
     }
 
 done_with_errmsg:
-    /* NULL checks for errmsg, mod_name, origin done by PyErr_SetImportError. */
-    _PyErr_SetImportErrorWithNameFrom(errmsg, mod_name, origin, name);
-    Py_DECREF(errmsg);
+    if (errmsg != NULL) {
+        /* NULL checks for errmsg, mod_name, origin done by _PyErr_SetImportErrorWithNameFrom */
+        _PyErr_SetImportErrorWithNameFrom(errmsg, mod_name, origin, name);
+        Py_DECREF(errmsg);
+    }
 
 done:
     Py_XDECREF(origin);