[3.5] bpo-29403: Fix mock's broken autospec behavior on method-bound builtin functions (GH-3)

Cython will, in the right circumstances, offer a MethodType instance
where im_func is a builtin function. Any instance of MethodType is
automatically assumed to be a Python-defined function (more
specifically, a function that has an inspectable signature), but
_set_signature was still conservative in its assumptions. As a result
_set_signature would return early with None instead of a mock since
the im_func had no inspectable signature. This causes problems
deeper inside mock, as _set_signature is assumed to _always_
return a mock, and nothing checked its return value.

In similar corner cases, autospec will simply not check the spec of the
function, so _set_signature is amended to now return early with the
original, not-wrapped mock object.

Patch by Aaron Gallagher.

(cherry picked from commit 856cbcc12f2e4cca93af5dc7ed6bcea4dd942f10)

1 files changed, 2 insertions, 0 deletions

diff --git a/Misc/NEWS.d/next/Library/2017-07-20-02-29-49.bpo-29403.3RinCV.rst b/Misc/NEWS.d/next/Library/2017-07-20-02-29-49.bpo-29403.3RinCV.rst
new file mode 100644
index 0000000..95bcd10
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-07-20-02-29-49.bpo-29403.3RinCV.rst
@@ -0,0 +1,2 @@
+Fix ``unittest.mock``'s autospec to not fail on method-bound builtin
+functions.  Patch by Aaron Gallagher.