Issue #21951: Fixed a crash in Tkinter on AIX when called Tcl command with

empty string or tuple argument.

On some platforms Tcl memory allocator returns NULL when allocating zero-sized
block of memory.

Lib/test/test_tcl.py

@@ -429,7 +429,6 @@ class TclTest(unittest.TestCase):
         self.assertEqual(passValue((1, '2', (3.4,))),
                          (1, '2', (3.4,)) if self.wantobjects else '1 2 3.4')
 
-    @unittest.skipIf(sys.platform.startswith("aix"), 'Issue #21951: crashes on AIX')
     def test_user_command(self):
         result = []
         def testfunc(arg):
@@ -456,9 +455,11 @@ class TclTest(unittest.TestCase):
         check('string')
         check('string\xbd')
         check('string\xe2\x82\xac', u'string\u20ac')
+        check('')
         check(u'string')
         check(u'string\xbd')
         check(u'string\u20ac')
+        check(u'')
         check('str\xc0\x80ing', u'str\x00ing')
         check('str\xc0\x80ing\xe2\x82\xac', u'str\x00ing\u20ac')
         check(u'str\x00ing')

Misc/NEWS

@@ -22,6 +22,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #21951: Fixed a crash in Tkinter on AIX when called Tcl command with
+  empty string or tuple argument.
+
 - Issue #21951: Tkinter now most likely raises MemoryError instead of crash
   if the memory allocation fails.
 

Modules/_tkinter.c

@@ -1052,6 +1052,8 @@ AsObj(PyObject *value)
         Py_ssize_t size, i;
 
         size = PyTuple_Size(value);
+        if (size == 0)
+            return Tcl_NewListObj(0, NULL);
         if (!CHECK_SIZE(size, sizeof(Tcl_Obj *))) {
             PyErr_SetString(PyExc_OverflowError, "tuple is too long");
             return NULL;
@@ -1075,6 +1077,8 @@ AsObj(PyObject *value)
         Tcl_UniChar *outbuf = NULL;
         Py_ssize_t i;
         size_t allocsize;
+        if (size == 0)
+            return Tcl_NewUnicodeObj((const void *)"", 0);
         if (!CHECK_SIZE(size, sizeof(Tcl_UniChar))) {
             PyErr_SetString(PyExc_OverflowError, "string is too long");
             return NULL;