bpo-35742: Fix test_envar_unimportable in test_builtin. (GH-11561)

Handle the case of an empty module name in PYTHONBREAKPOINT.

Fixes a regression introduced in bpo-34756.
(cherry picked from commit 3607ef43c4a1a24d44f39ff54a77fc0af5bfa09a)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

1 files changed, 15 insertions, 10 deletions

diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 75e4f4bf29..cdc2edf038 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -134,11 +134,14 @@ sys_breakpointhook(PyObject *self, PyObject *const *args, Py_ssize_t nargs, PyOb
         modulepath = PyUnicode_FromString("builtins");
         attrname = envar;
     }
-    else {
+    else if (last_dot != envar) {
         /* Split on the last dot; */
         modulepath = PyUnicode_FromStringAndSize(envar, last_dot - envar);
         attrname = last_dot + 1;
     }
+    else {
+        goto warn;
+    }
     if (modulepath == NULL) {
         PyMem_RawFree(envar);
         return NULL;
@@ -156,27 +159,29 @@ sys_breakpointhook(PyObject *self, PyObject *const *args, Py_ssize_t nargs, PyOb
     Py_DECREF(fromlist);
 
     if (module == NULL) {
-        goto error;
+        if (PyErr_ExceptionMatches(PyExc_ImportError)) {
+            goto warn;
+        }
+        PyMem_RawFree(envar);
+        return NULL;
     }
 
     PyObject *hook = PyObject_GetAttrString(module, attrname);
     Py_DECREF(module);
 
     if (hook == NULL) {
-        goto error;
+        if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
+            goto warn;
+        }
+        PyMem_RawFree(envar);
+        return NULL;
     }
     PyMem_RawFree(envar);
     PyObject *retval = _PyObject_FastCallKeywords(hook, args, nargs, keywords);
     Py_DECREF(hook);
     return retval;
 
-  error:
-    if (!PyErr_ExceptionMatches(PyExc_ImportError)
-        && !PyErr_ExceptionMatches(PyExc_AttributeError))
-    {
-        PyMem_RawFree(envar);
-        return NULL;
-    }
+  warn:
     /* If any of the imports went wrong, then warn and ignore. */
     PyErr_Clear();
     int status = PyErr_WarnFormat(