subprocess: Fix patched functions with optional arguments

Since [1] we monkey patch subprocess module and it uncovered one issue -
the previous patched_function implementation would produce functions
with all optional arguments lacking their default values which made them
required. This is an issue on Python 3 where there's at least one
optional explicit argument in at least one of the functions
(check_call), on Python 2 the function signature has *args and **kwargs
so it wasn't an issue.

This patch is contributed by Smarkets Limited.

[1] 614a20462a

eventlet/green/subprocess.py

@@ -119,7 +119,11 @@ class Popen(subprocess_orig.Popen):
 # Borrow subprocess.call() and check_call(), but patch them so they reference
 # OUR Popen class rather than subprocess.Popen.
 def patched_function(function):
-    return FunctionType(six.get_function_code(function), globals())
+    new_function = FunctionType(six.get_function_code(function), globals())
+    if six.PY3:
+        new_function.__kwdefaults__ = function.__kwdefaults__
+    new_function.__defaults__ = function.__defaults__
+    return new_function
 
 
 call = patched_function(subprocess_orig.call)

tests/subprocess_test.py

@@ -83,3 +83,13 @@ def test_patched_communicate_290():
     # with AttributeError module `select` has no `poll` on Linux
     # unpatched methods are removed for safety reasons in commit f63165c0e3
     tests.run_isolated('subprocess_patched_communicate.py')
+
+
+def test_check_call_without_timeout_works():
+    # There was a regression that'd result in the following exception:
+    # TypeError: check_call() missing 1 required keyword-only argument: 'timeout'
+    subprocess.check_call(
+        ['ls'],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+    )