# HG changeset patch
# Parent 4e84e45e191b3b063387fdd68075f47f4576e215
Issue #22836: Keep exception reports sensible despite errors

diff -r 4e84e45e191b Doc/c-api/exceptions.rst
--- a/Doc/c-api/exceptions.rst	Fri Dec 19 11:21:56 2014 -0500
+++ b/Doc/c-api/exceptions.rst	Sat Dec 20 04:17:36 2014 +0000
@@ -74,8 +74,8 @@
    :meth:`__del__` method.
 
    The function is called with a single argument *obj* that identifies the context
-   in which the unraisable exception occurred. The repr of *obj* will be printed in
-   the warning message.
+   in which the unraisable exception occurred. If possible,
+   the repr of *obj* will be printed in the warning message.
 
 
 Raising exceptions
diff -r 4e84e45e191b Lib/test/test_exceptions.py
--- a/Lib/test/test_exceptions.py	Fri Dec 19 11:21:56 2014 -0500
+++ b/Lib/test/test_exceptions.py	Sat Dec 20 04:17:36 2014 +0000
@@ -7,9 +7,10 @@
 import weakref
 import errno
 
-from test.support import (TESTFN, captured_output, check_impl_detail,
+from test.support import (TESTFN, captured_stderr, check_impl_detail,
                           check_warnings, cpython_only, gc_collect, run_unittest,
                           no_tracing, unlink)
+from test.script_helper import assert_python_failure
 
 class NaiveException(Exception):
     def __init__(self, x):
@@ -816,7 +817,7 @@
         class MyException(Exception, metaclass=Meta):
             pass
 
-        with captured_output("stderr") as stderr:
+        with captured_stderr() as stderr:
             try:
                 raise KeyError()
             except MyException as e:
@@ -945,6 +946,66 @@
             os.listdir(__file__)
         self.assertEqual(cm.exception.errno, errno.ENOTDIR, cm.exception)
 
+    def test_unraisable(self):
+        '''Check for sensible reports from PyErr_WriteUnraisable() (Issue
+        22836)'''
+        class BrokenDel:
+            def __del__(self):
+                raise Exception("del is broken")
+        class BrokenRepr(BrokenDel):
+            def __repr__(self):
+                raise Exception("repr() is broken")
+        class BrokenException(Exception):
+            def __str__(self):
+                raise BrokenException("Exception is broken")
+        class BrokenExceptionDel:
+            def __del__(self):
+                raise BrokenException()
+        for test_class in (BrokenDel, BrokenRepr, BrokenExceptionDel):
+            with self.subTest(test_class):
+                obj = test_class()
+                with captured_stderr() as stderr:
+                    del obj
+                stderr = stderr.getvalue()
+                self.assertIn("Exception ignored", stderr)
+                if test_class is not BrokenRepr:
+                    self.assertIn(test_class.__del__.__qualname__, stderr)
+                self.assertIn("raise", stderr)
+                if test_class is BrokenExceptionDel:
+                    self.assertIn("BrokenException:", stderr)
+                else:
+                    self.assertIn("Exception: del is broken", stderr)
+                self.assertTrue(stderr.endswith("\n"))
+
+    def test_unhandled(self):
+        '''Check for sensible reporting of unhandled exceptions'''
+        tests = (
+            dict(
+                desc="Working exception",
+                script=r'''raise Exception("dummy message")''',
+                details=(b"line", b"Exception: dummy message"),
+            ),
+            dict(
+                desc="Broken exception",
+                script=
+                    '''class BrokenException(Exception):\n'''
+                    '''    def __str__(self):\n'''
+                    '''        raise Exception("Exception is broken")\n'''
+                    '''raise BrokenException()\n''',
+                details=(b"line", b"BrokenException:"),
+            ),
+        )
+        for test in tests:
+            with self.subTest(test["desc"]):
+                # Avoid conflicting with potential debug output on stderr
+                script = '''import sys; sys.stderr = sys.stdout\n'''
+                script += test["script"]
+                [rc, report, _] = assert_python_failure("-c", script)
+                self.assertEqual(1, rc)
+                for detail in test["details"]:
+                    self.assertIn(detail, report)
+                self.assertTrue(report.endswith(b"\n"))
+
 
 class ImportErrorTests(unittest.TestCase):
 
diff -r 4e84e45e191b Python/errors.c
--- a/Python/errors.c	Fri Dec 19 11:21:56 2014 -0500
+++ b/Python/errors.c	Sat Dec 20 04:17:36 2014 +0000
@@ -910,8 +910,12 @@
     if (obj) {
         if (PyFile_WriteString("Exception ignored in: ", f) < 0)
             goto done;
-        if (PyFile_WriteObject(obj, f, 0) < 0)
-            goto done;
+        if (PyFile_WriteObject(obj, f, 0) < 0) {
+            PyErr_Clear();
+            if (PyFile_WriteString("<repr() failed>", f) < 0) {
+                goto done;
+            }
+        }
         if (PyFile_WriteString("\n", f) < 0)
             goto done;
     }
@@ -956,8 +960,12 @@
     if (v && v != Py_None) {
         if (PyFile_WriteString(": ", f) < 0)
             goto done;
-        if (PyFile_WriteObject(v, f, Py_PRINT_RAW) < 0)
-            goto done;
+        if (PyFile_WriteObject(v, f, Py_PRINT_RAW) < 0) {
+            PyErr_Clear();
+            if (PyFile_WriteString("<str() failed>", f) < 0) {
+                goto done;
+            }
+        }
     }
     if (PyFile_WriteString("\n", f) < 0)
         goto done;
diff -r 4e84e45e191b Python/pythonrun.c
--- a/Python/pythonrun.c	Fri Dec 19 11:21:56 2014 -0500
+++ b/Python/pythonrun.c	Sat Dec 20 04:17:36 2014 +0000
@@ -764,8 +764,11 @@
         /* only print colon if the str() of the
            object is not the empty string
         */
-        if (s == NULL)
+        if (s == NULL) {
+            PyErr_Clear();
             err = -1;
+            err += PyFile_WriteString(": <str() failed>", f);
+        }
         else if (!PyUnicode_Check(s) ||
             PyUnicode_GetLength(s) != 0)
             err = PyFile_WriteString(": ", f);
@@ -774,6 +777,9 @@
         Py_XDECREF(s);
     }
     /* try to write a newline in any case */
+    if (err < 0) {
+        PyErr_Clear();
+    }
     err += PyFile_WriteString("\n", f);
     Py_XDECREF(tb);
     Py_DECREF(value);