Issue #25791: Warn when __package__ != __spec__.parent.

In a previous change, __spec__.parent was prioritized over
__package__. That is a backwards-compatibility break, but we do
eventually want __spec__ to be the ground truth for module details. So
this change reverts the change in semantics and instead raises an
ImportWarning when __package__ != __spec__.parent to give people time
to adjust to using spec objects.

2 files changed, 121 insertions, 93 deletions

diff --git a/Python/import.c b/Python/import.c
index c1071c0..22f9d21 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -1415,60 +1415,79 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *given_globals,
         goto error;
     }
     else if (level > 0) {
+        package = _PyDict_GetItemId(globals, &PyId___package__);
         spec = _PyDict_GetItemId(globals, &PyId___spec__);
-        if (spec != NULL) {
-            package = PyObject_GetAttrString(spec, "parent");
-        }
+
         if (package != NULL && package != Py_None) {
+            Py_INCREF(package);
             if (!PyUnicode_Check(package)) {
+                PyErr_SetString(PyExc_TypeError, "package must be a string");
+                goto error;
+            }
+            else if (spec != NULL) {
+                int equal;
+                PyObject *parent = PyObject_GetAttrString(spec, "parent");
+                if (parent == NULL) {
+                    goto error;
+                }
+
+                equal = PyObject_RichCompareBool(package, parent, Py_EQ);
+                Py_DECREF(parent);
+                if (equal < 0) {
+                    goto error;
+                }
+                else if (equal == 0) {
+                    if (PyErr_WarnEx(PyExc_ImportWarning,
+                            "__package__ != __spec__.parent", 1) < 0) {
+                        goto error;
+                    }
+                }
+            }
+        }
+        else if (spec != NULL) {
+            package = PyObject_GetAttrString(spec, "parent");
+            if (package == NULL) {
+                goto error;
+            }
+            else if (!PyUnicode_Check(package)) {
                 PyErr_SetString(PyExc_TypeError,
                         "__spec__.parent must be a string");
                 goto error;
             }
         }
         else {
-            package = _PyDict_GetItemId(globals, &PyId___package__);
-            if (package != NULL && package != Py_None) {
-                Py_INCREF(package);
-                if (!PyUnicode_Check(package)) {
-                    PyErr_SetString(PyExc_TypeError, "package must be a string");
-                    goto error;
-                }
+            if (PyErr_WarnEx(PyExc_ImportWarning,
+                        "can't resolve package from __spec__ or __package__, "
+                        "falling back on __name__ and __path__", 1) < 0) {
+                goto error;
             }
-            else {
-                if (PyErr_WarnEx(PyExc_ImportWarning,
-                            "can't resolve package from __spec__ or __package__, "
-                            "falling back on __name__ and __path__", 1) < 0) {
-                    goto error;
-                }
 
-                package = _PyDict_GetItemId(globals, &PyId___name__);
-                if (package == NULL) {
-                    PyErr_SetString(PyExc_KeyError, "'__name__' not in globals");
-                    goto error;
-                }
+            package = _PyDict_GetItemId(globals, &PyId___name__);
+            if (package == NULL) {
+                PyErr_SetString(PyExc_KeyError, "'__name__' not in globals");
+                goto error;
+            }
 
-                Py_INCREF(package);
-                if (!PyUnicode_Check(package)) {
-                    PyErr_SetString(PyExc_TypeError, "__name__ must be a string");
+            Py_INCREF(package);
+            if (!PyUnicode_Check(package)) {
+                PyErr_SetString(PyExc_TypeError, "__name__ must be a string");
+                goto error;
+            }
+
+            if (_PyDict_GetItemId(globals, &PyId___path__) == NULL) {
+                PyObject *partition = NULL;
+                PyObject *borrowed_dot = _PyUnicode_FromId(&single_dot);
+                if (borrowed_dot == NULL) {
                     goto error;
                 }
-
-                if (_PyDict_GetItemId(globals, &PyId___path__) == NULL) {
-                    PyObject *partition = NULL;
-                    PyObject *borrowed_dot = _PyUnicode_FromId(&single_dot);
-                    if (borrowed_dot == NULL) {
-                        goto error;
-                    }
-                    partition = PyUnicode_RPartition(package, borrowed_dot);
-                    Py_DECREF(package);
-                    if (partition == NULL) {
-                        goto error;
-                    }
-                    package = PyTuple_GET_ITEM(partition, 0);
-                    Py_INCREF(package);
-                    Py_DECREF(partition);
+                partition = PyUnicode_RPartition(package, borrowed_dot);
+                Py_DECREF(package);
+                if (partition == NULL) {
+                    goto error;
                 }
+                package = PyTuple_GET_ITEM(partition, 0);
+                Py_INCREF(package);
+                Py_DECREF(partition);
             }
         }
 
diff --git a/Python/importlib.h b/Python/importlib.h
index 709c5fd..e4ef835 100644
--- a/Python/importlib.h
+++ b/Python/importlib.h
@@ -1787,43 +1787,52 @@ const unsigned char _Py_M__importlib[] = {
     115,116,228,3,0,0,115,34,0,0,0,0,10,15,1,12,
     1,12,1,13,1,15,1,16,1,13,1,15,1,21,1,3,
     1,17,1,18,4,21,1,15,1,3,1,26,1,114,195,0,
-    0,0,99,1,0,0,0,0,0,0,0,3,0,0,0,5,
-    0,0,0,67,0,0,0,115,128,0,0,0,124,0,0,106,
-    0,0,100,1,0,131,1,0,125,1,0,124,1,0,100,2,
-    0,107,9,0,114,34,0,124,1,0,106,1,0,83,124,0,
-    0,106,0,0,100,3,0,131,1,0,125,2,0,124,2,0,
-    100,2,0,107,8,0,114,124,0,116,2,0,106,3,0,100,
-    4,0,116,4,0,100,5,0,100,6,0,131,2,1,1,124,
-    0,0,100,7,0,25,125,2,0,100,8,0,124,0,0,107,
-    7,0,114,124,0,124,2,0,106,5,0,100,9,0,131,1,
-    0,100,10,0,25,125,2,0,124,2,0,83,41,11,122,167,
-    67,97,108,99,117,108,97,116,101,32,119,104,97,116,32,95,
-    95,112,97,99,107,97,103,101,95,95,32,115,104,111,117,108,
-    100,32,98,101,46,10,10,32,32,32,32,95,95,112,97,99,
-    107,97,103,101,95,95,32,105,115,32,110,111,116,32,103,117,
-    97,114,97,110,116,101,101,100,32,116,111,32,98,101,32,100,
-    101,102,105,110,101,100,32,111,114,32,99,111,117,108,100,32,
-    98,101,32,115,101,116,32,116,111,32,78,111,110,101,10,32,
-    32,32,32,116,111,32,114,101,112,114,101,115,101,110,116,32,
-    116,104,97,116,32,105,116,115,32,112,114,111,112,101,114,32,
-    118,97,108,117,101,32,105,115,32,117,110,107,110,111,119,110,
-    46,10,10,32,32,32,32,114,95,0,0,0,78,114,134,0,
-    0,0,122,89,99,97,110,39,116,32,114,101,115,111,108,118,
-    101,32,112,97,99,107,97,103,101,32,102,114,111,109,32,95,
-    95,115,112,101,99,95,95,32,111,114,32,95,95,112,97,99,
-    107,97,103,101,95,95,44,32,102,97,108,108,105,110,103,32,
-    98,97,99,107,32,111,110,32,95,95,110,97,109,101,95,95,
-    32,97,110,100,32,95,95,112,97,116,104,95,95,114,140,0,
-    0,0,233,3,0,0,0,114,1,0,0,0,114,131,0,0,
-    0,114,121,0,0,0,114,33,0,0,0,41,6,114,42,0,
-    0,0,114,123,0,0,0,114,142,0,0,0,114,143,0,0,
-    0,114,176,0,0,0,114,122,0,0,0,41,3,218,7,103,
-    108,111,98,97,108,115,114,88,0,0,0,114,170,0,0,0,
-    114,10,0,0,0,114,10,0,0,0,114,11,0,0,0,218,
-    17,95,99,97,108,99,95,95,95,112,97,99,107,97,103,101,
-    95,95,4,4,0,0,115,22,0,0,0,0,7,15,1,12,
-    1,7,1,15,1,12,1,9,2,13,1,10,1,12,1,19,
-    1,114,198,0,0,0,99,5,0,0,0,0,0,0,0,9,
+    0,0,99,1,0,0,0,0,0,0,0,3,0,0,0,7,
+    0,0,0,67,0,0,0,115,214,0,0,0,124,0,0,106,
+    0,0,100,1,0,131,1,0,125,1,0,124,0,0,106,0,
+    0,100,2,0,131,1,0,125,2,0,124,1,0,100,3,0,
+    107,9,0,114,128,0,124,2,0,100,3,0,107,9,0,114,
+    124,0,124,1,0,124,2,0,106,1,0,107,3,0,114,124,
+    0,116,2,0,106,3,0,100,4,0,106,4,0,100,5,0,
+    124,1,0,155,2,0,100,6,0,124,2,0,106,1,0,155,
+    2,0,100,7,0,103,5,0,131,1,0,116,5,0,100,8,
+    0,100,9,0,131,2,1,1,124,1,0,83,124,2,0,100,
+    3,0,107,9,0,114,147,0,124,2,0,106,1,0,83,116,
+    2,0,106,3,0,100,10,0,116,5,0,100,8,0,100,9,
+    0,131,2,1,1,124,0,0,100,11,0,25,125,1,0,100,
+    12,0,124,0,0,107,7,0,114,210,0,124,1,0,106,6,
+    0,100,13,0,131,1,0,100,14,0,25,125,1,0,124,1,
+    0,83,41,15,122,167,67,97,108,99,117,108,97,116,101,32,
+    119,104,97,116,32,95,95,112,97,99,107,97,103,101,95,95,
+    32,115,104,111,117,108,100,32,98,101,46,10,10,32,32,32,
+    32,95,95,112,97,99,107,97,103,101,95,95,32,105,115,32,
+    110,111,116,32,103,117,97,114,97,110,116,101,101,100,32,116,
+    111,32,98,101,32,100,101,102,105,110,101,100,32,111,114,32,
+    99,111,117,108,100,32,98,101,32,115,101,116,32,116,111,32,
+    78,111,110,101,10,32,32,32,32,116,111,32,114,101,112,114,
+    101,115,101,110,116,32,116,104,97,116,32,105,116,115,32,112,
+    114,111,112,101,114,32,118,97,108,117,101,32,105,115,32,117,
+    110,107,110,111,119,110,46,10,10,32,32,32,32,114,134,0,
+    0,0,114,95,0,0,0,78,218,0,122,32,95,95,112,97,
+    99,107,97,103,101,95,95,32,33,61,32,95,95,115,112,101,
+    99,95,95,46,112,97,114,101,110,116,32,40,122,4,32,33,
+    61,32,250,1,41,114,140,0,0,0,233,3,0,0,0,122,
+    89,99,97,110,39,116,32,114,101,115,111,108,118,101,32,112,
+    97,99,107,97,103,101,32,102,114,111,109,32,95,95,115,112,
+    101,99,95,95,32,111,114,32,95,95,112,97,99,107,97,103,
+    101,95,95,44,32,102,97,108,108,105,110,103,32,98,97,99,
+    107,32,111,110,32,95,95,110,97,109,101,95,95,32,97,110,
+    100,32,95,95,112,97,116,104,95,95,114,1,0,0,0,114,
+    131,0,0,0,114,121,0,0,0,114,33,0,0,0,41,7,
+    114,42,0,0,0,114,123,0,0,0,114,142,0,0,0,114,
+    143,0,0,0,114,115,0,0,0,114,176,0,0,0,114,122,
+    0,0,0,41,3,218,7,103,108,111,98,97,108,115,114,170,
+    0,0,0,114,88,0,0,0,114,10,0,0,0,114,10,0,
+    0,0,114,11,0,0,0,218,17,95,99,97,108,99,95,95,
+    95,112,97,99,107,97,103,101,95,95,4,4,0,0,115,30,
+    0,0,0,0,7,15,1,15,1,12,1,27,1,42,2,13,
+    1,4,1,12,1,7,2,9,2,13,1,10,1,12,1,19,
+    1,114,200,0,0,0,99,5,0,0,0,0,0,0,0,9,
     0,0,0,5,0,0,0,67,0,0,0,115,227,0,0,0,
     124,4,0,100,1,0,107,2,0,114,27,0,116,0,0,124,
     0,0,131,1,0,125,5,0,110,54,0,124,1,0,100,2,
@@ -1870,17 +1879,17 @@ const unsigned char _Py_M__importlib[] = {
     111,117,108,100,32,104,97,118,101,32,97,32,39,108,101,118,
     101,108,39,32,111,102,32,50,41,46,10,10,32,32,32,32,
     114,33,0,0,0,78,114,121,0,0,0,41,8,114,187,0,
-    0,0,114,198,0,0,0,218,9,112,97,114,116,105,116,105,
+    0,0,114,200,0,0,0,218,9,112,97,114,116,105,116,105,
     111,110,114,168,0,0,0,114,14,0,0,0,114,21,0,0,
     0,114,1,0,0,0,114,195,0,0,0,41,9,114,15,0,
-    0,0,114,197,0,0,0,218,6,108,111,99,97,108,115,114,
+    0,0,114,199,0,0,0,218,6,108,111,99,97,108,115,114,
     193,0,0,0,114,171,0,0,0,114,89,0,0,0,90,8,
     103,108,111,98,97,108,115,95,114,170,0,0,0,90,7,99,
     117,116,95,111,102,102,114,10,0,0,0,114,10,0,0,0,
     114,11,0,0,0,218,10,95,95,105,109,112,111,114,116,95,
-    95,25,4,0,0,115,26,0,0,0,0,11,12,1,15,2,
+    95,31,4,0,0,115,26,0,0,0,0,11,12,1,15,2,
     24,1,12,1,18,1,6,3,12,1,23,1,6,1,4,4,
-    35,3,40,2,114,201,0,0,0,99,1,0,0,0,0,0,
+    35,3,40,2,114,203,0,0,0,99,1,0,0,0,0,0,
     0,0,2,0,0,0,3,0,0,0,67,0,0,0,115,53,
     0,0,0,116,0,0,106,1,0,124,0,0,131,1,0,125,
     1,0,124,1,0,100,0,0,107,8,0,114,43,0,116,2,
@@ -1891,8 +1900,8 @@ const unsigned char _Py_M__importlib[] = {
     0,0,114,77,0,0,0,114,150,0,0,0,41,2,114,15,
     0,0,0,114,88,0,0,0,114,10,0,0,0,114,10,0,
     0,0,114,11,0,0,0,218,18,95,98,117,105,108,116,105,
-    110,95,102,114,111,109,95,110,97,109,101,60,4,0,0,115,
-    8,0,0,0,0,1,15,1,12,1,16,1,114,202,0,0,
+    110,95,102,114,111,109,95,110,97,109,101,66,4,0,0,115,
+    8,0,0,0,0,1,15,1,12,1,16,1,114,204,0,0,
     0,99,2,0,0,0,0,0,0,0,12,0,0,0,12,0,
     0,0,67,0,0,0,115,74,1,0,0,124,1,0,97,0,
     0,124,0,0,97,1,0,116,2,0,116,1,0,131,1,0,
@@ -1937,7 +1946,7 @@ const unsigned char _Py_M__importlib[] = {
     0,114,21,0,0,0,218,5,105,116,101,109,115,114,178,0,
     0,0,114,76,0,0,0,114,151,0,0,0,114,82,0,0,
     0,114,161,0,0,0,114,132,0,0,0,114,137,0,0,0,
-    114,1,0,0,0,114,202,0,0,0,114,5,0,0,0,114,
+    114,1,0,0,0,114,204,0,0,0,114,5,0,0,0,114,
     77,0,0,0,41,12,218,10,115,121,115,95,109,111,100,117,
     108,101,218,11,95,105,109,112,95,109,111,100,117,108,101,90,
     11,109,111,100,117,108,101,95,116,121,112,101,114,15,0,0,
@@ -1948,10 +1957,10 @@ const unsigned char _Py_M__importlib[] = {
     101,97,100,95,109,111,100,117,108,101,90,14,119,101,97,107,
     114,101,102,95,109,111,100,117,108,101,114,10,0,0,0,114,
     10,0,0,0,114,11,0,0,0,218,6,95,115,101,116,117,
-    112,67,4,0,0,115,50,0,0,0,0,9,6,1,6,3,
+    112,73,4,0,0,115,50,0,0,0,0,9,6,1,6,3,
     12,1,28,1,15,1,15,1,9,1,15,1,9,2,3,1,
     15,1,17,3,13,1,13,1,15,1,15,2,13,1,20,3,
-    3,1,16,1,13,2,11,1,16,3,12,1,114,206,0,0,
+    3,1,16,1,13,2,11,1,16,3,12,1,114,208,0,0,
     0,99,2,0,0,0,0,0,0,0,3,0,0,0,3,0,
     0,0,67,0,0,0,115,87,0,0,0,116,0,0,124,0,
     0,124,1,0,131,2,0,1,116,1,0,106,2,0,106,3,
@@ -1963,15 +1972,15 @@ const unsigned char _Py_M__importlib[] = {
     112,111,114,116,108,105,98,32,97,115,32,116,104,101,32,105,
     109,112,108,101,109,101,110,116,97,116,105,111,110,32,111,102,
     32,105,109,112,111,114,116,46,114,33,0,0,0,78,41,11,
-    114,206,0,0,0,114,14,0,0,0,114,175,0,0,0,114,
+    114,208,0,0,0,114,14,0,0,0,114,175,0,0,0,114,
     113,0,0,0,114,151,0,0,0,114,161,0,0,0,218,26,
     95,102,114,111,122,101,110,95,105,109,112,111,114,116,108,105,
     98,95,101,120,116,101,114,110,97,108,114,119,0,0,0,218,
     8,95,105,110,115,116,97,108,108,114,21,0,0,0,114,1,
-    0,0,0,41,3,114,204,0,0,0,114,205,0,0,0,114,
-    207,0,0,0,114,10,0,0,0,114,10,0,0,0,114,11,
-    0,0,0,114,208,0,0,0,114,4,0,0,115,12,0,0,
-    0,0,2,13,2,16,1,16,3,12,1,6,1,114,208,0,
+    0,0,0,41,3,114,206,0,0,0,114,207,0,0,0,114,
+    209,0,0,0,114,10,0,0,0,114,10,0,0,0,114,11,
+    0,0,0,114,210,0,0,0,120,4,0,0,115,12,0,0,
+    0,0,2,13,2,16,1,16,3,12,1,6,1,114,210,0,
     0,0,41,51,114,3,0,0,0,114,119,0,0,0,114,12,
     0,0,0,114,16,0,0,0,114,17,0,0,0,114,59,0,
     0,0,114,41,0,0,0,114,48,0,0,0,114,31,0,0,
@@ -1987,8 +1996,8 @@ const unsigned char _Py_M__importlib[] = {
     0,114,172,0,0,0,114,174,0,0,0,114,177,0,0,0,
     114,182,0,0,0,114,192,0,0,0,114,183,0,0,0,114,
     185,0,0,0,114,186,0,0,0,114,187,0,0,0,114,195,
-    0,0,0,114,198,0,0,0,114,201,0,0,0,114,202,0,
-    0,0,114,206,0,0,0,114,208,0,0,0,114,10,0,0,
+    0,0,0,114,200,0,0,0,114,203,0,0,0,114,204,0,
+    0,0,114,208,0,0,0,114,210,0,0,0,114,10,0,0,
     0,114,10,0,0,0,114,10,0,0,0,114,11,0,0,0,
     218,8,60,109,111,100,117,108,101,62,8,0,0,0,115,96,
     0,0,0,6,17,6,2,12,8,12,4,19,20,6,2,6,
@@ -1996,6 +2005,6 @@ const unsigned char _Py_M__importlib[] = {
     8,12,11,12,12,12,16,12,36,19,27,19,101,24,26,9,
     3,18,45,18,60,12,18,12,17,12,25,12,29,12,23,12,
     16,19,73,19,77,19,13,12,9,12,9,15,40,12,17,6,
-    1,10,2,12,27,12,6,18,24,12,32,12,21,24,35,12,
+    1,10,2,12,27,12,6,18,24,12,32,12,27,24,35,12,
     7,12,47,
 };