Fix flake8 io deadlock (#757)

Co-authored-by: Carlos Cordoba <[email protected]>

Author: rdugan

pyls/plugins/flake8_lint.py

@@ -58,11 +58,10 @@ def run_flake8(args):
         cmd = ['python', '-m', 'flake8']
         cmd.extend(args)
         p = Popen(cmd, stdout=PIPE, stderr=PIPE)
-    stderr = p.stderr.read().decode()
+    (stdout, stderr) = p.communicate()
     if stderr:
-        log.error("Error while running flake8 '%s'", stderr)
-    stdout = p.stdout
-    return stdout.read().decode()
+        log.error("Error while running flake8 '%s'", stderr.decode())
+    return stdout.decode()
 
 
 def build_args(options, doc_path):

test/plugins/test_flake8_lint.py

@@ -57,6 +57,8 @@ def test_flake8_lint(config):
 
 def test_flake8_config_param(config):
     with patch('pyls.plugins.flake8_lint.Popen') as popen_mock:
+        mock_instance = popen_mock.return_value
+        mock_instance.communicate.return_value = [bytes(), bytes()]
         flake8_conf = '/tmp/some.cfg'
         config.update({'plugins': {'flake8': {'config': flake8_conf}}})
         _name, doc = temp_document(DOC)