From acb3e8e8a797a1fd321322d27114ef15ff99d440 Mon Sep 17 00:00:00 2001
From: Anton Lodder <alodder@opusonesolutions.com>
Date: Thu, 10 Jan 2019 14:12:50 -0500
Subject: [PATCH 1/3] Test rewriting assertion when __name__ fails

Pytest rewrites assertions so that the items on each
side of a comoparison will have easier-to-read names
in case of an assertion error.

Before doing this, it checks to make sure the object
doesn't have a __name__ attribute; however, it uses
`hasattr` so if the objects __getattr__ is broken then
the test failure message will be the stack trace
for this failure instead of a rewritten assertion.
---
 testing/test_assertrewrite.py | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/testing/test_assertrewrite.py b/testing/test_assertrewrite.py
index 4187e365b6d..840fda2ca9a 100644
--- a/testing/test_assertrewrite.py
+++ b/testing/test_assertrewrite.py
@@ -180,6 +180,27 @@ class X(object):
 
         assert getmsg(f, {"cls": X}) == "assert cls == 42"
 
+    def test_dont_rewrite_if_hasattr_fails(self):
+        class Y(object):
+            """ A class whos getattr fails, but not with `AttributeError` """
+
+            def __getattr__(self, attribute_name):
+                raise KeyError()
+
+            def __repr__(self):
+                return "Y"
+
+            def __init__(self):
+                self.foo = 3
+
+        def f():
+            assert cls().foo == 2  # noqa
+
+        message = getmsg(f, {"cls": Y})
+        assert "assert 3 == 2" in message
+        assert "+  where 3 = Y.foo" in message
+        assert "+    where Y = cls()" in message
+
     def test_assert_already_has_message(self):
         def f():
             assert False, "something bad!"

From 3241fc31030cc2d9cc9870fb388fabcab541fbe5 Mon Sep 17 00:00:00 2001
From: Anton Lodder <alodder@opusonesolutions.com>
Date: Thu, 10 Jan 2019 14:13:17 -0500
Subject: [PATCH 2/3] Don't fail if hasattr fails when rewriting assertions

When rewriting assertions, pytest makes a call to
`__name__` on each object in a comparision. If one of
the objects has reimplemented `__getattr__`, they could
fail trying to fetch `__name__` with an error other than
`AttributeError`, which is what `hasattr` catches.

In this case, the stack trace for the failed `__getattr__`
call will show up in the pytest output, even though
it isn't related to the test failing.

This change fixes that by catching exceptions
that `hasattr` throws.
---
 src/_pytest/assertion/rewrite.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/_pytest/assertion/rewrite.py b/src/_pytest/assertion/rewrite.py
index 1d2c27ed152..df8b9becbb4 100644
--- a/src/_pytest/assertion/rewrite.py
+++ b/src/_pytest/assertion/rewrite.py
@@ -525,7 +525,13 @@ def _format_assertmsg(obj):
 
 
 def _should_repr_global_name(obj):
-    return not hasattr(obj, "__name__") and not callable(obj)
+    if callable(obj):
+        return False
+
+    try:
+        return not hasattr(obj, "__name__")
+    except Exception:
+        return True
 
 
 def _format_boolop(explanations, is_or):

From 77da4f118c81a6c28b4be0f931fa4d8bd512fb69 Mon Sep 17 00:00:00 2001
From: Anton Lodder <alodder@opusonesolutions.com>
Date: Thu, 10 Jan 2019 14:27:10 -0500
Subject: [PATCH 3/3] Add changelog 4631 and AUTHOR credits for Anton Lodder

---
 AUTHORS                   | 1 +
 changelog/4631.bugfix.rst | 1 +
 2 files changed, 2 insertions(+)
 create mode 100644 changelog/4631.bugfix.rst

diff --git a/AUTHORS b/AUTHORS
index 7ce822b4329..06947d17be9 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -24,6 +24,7 @@ Andy Freeland
 Anthon van der Neut
 Anthony Shaw
 Anthony Sottile
+Anton Lodder
 Antony Lee
 Armin Rigo
 Aron Coyle
diff --git a/changelog/4631.bugfix.rst b/changelog/4631.bugfix.rst
new file mode 100644
index 00000000000..df929e8afd4
--- /dev/null
+++ b/changelog/4631.bugfix.rst
@@ -0,0 +1 @@
+Don't rewrite assertion when ``__getattr__`` is broken