chore(mypy): re-enable the mypy gate in Travis (falconry#1698)

.travis.yml

@@ -15,10 +15,8 @@ matrix:
           env: TOXENV=pep8
         - python: 3.8
           env: TOXENV=pep8-examples
-        # TODO(vytas): Re-enable once we have fixed mypy warnings.
-        #   They have been lurking for a while, just underreported.
-        # - python: 3.8
-        #   env: TOXENV=mypy
+        - python: 3.8
+          env: TOXENV=mypy
           # NOTE(kgriffs):  3.5.2 is the default Python 3 version on Ubuntu 16.04
           #   so we pin to that for testing to make sure we are working around
           #   and quirks that were fixed in later micro versions.

falcon/asgi/response.py

@@ -14,7 +14,7 @@
 
 """ASGI Response class."""
 
-from asyncio.coroutines import CoroWrapper
+from asyncio.coroutines import CoroWrapper  # type: ignore
 from inspect import iscoroutine, iscoroutinefunction
 
 from falcon import _UNSET

falcon/media/handlers.py

@@ -63,4 +63,4 @@ def find_by_media_type(self, media_type, default):
     'application/json': JSONHandler(),
     'application/json; charset=UTF-8': JSONHandler(),
     MEDIA_URLENCODED: URLEncodedFormHandler(),
-})
+})  # type: ignore

falcon/testing/helpers.py

@@ -116,7 +116,7 @@ class ASGIRequestEventEmitter:
 
     # TODO(kgriffs): If this pattern later becomes useful elsewhere,
     #   factor out into a standalone helper class.
-    _branch_decider = defaultdict(bool)
+    _branch_decider = defaultdict(bool)  # type: defaultdict
 
     def __init__(self, body=None, disconnect_at=None, chunk_size=4096):
         if body is None:

falcon/util/misc.py

@@ -85,7 +85,7 @@ def decorator(func):
 ):
     _lru_cache_safe = _lru_cache_nop  # pragma: nocover
 else:
-    _lru_cache_safe = functools.lru_cache
+    _lru_cache_safe = functools.lru_cache  # type: ignore
 
 
 def is_python_func(func):

falcon/util/sync.py

@@ -1,9 +1,9 @@
 import asyncio
-from collections.abc import Coroutine
 from concurrent.futures import ThreadPoolExecutor
 from functools import partial, wraps
 import inspect
 import os
+from typing import Callable
 
 
 __all__ = [
@@ -29,7 +29,7 @@
     """Gets the running asyncio event loop."""
 
 
-def wrap_sync_to_async_unsafe(func) -> Coroutine:
+def wrap_sync_to_async_unsafe(func) -> Callable:
     """Wrap a callable in a coroutine that executes the callable directly.
 
     This helper makes it easier to use synchronous callables with ASGI
@@ -59,7 +59,7 @@ async def wrapper(*args, **kwargs):
     return wrapper
 
 
-def wrap_sync_to_async(func, threadsafe=None) -> Coroutine:
+def wrap_sync_to_async(func, threadsafe=None) -> Callable:
     """Wrap a callable in a coroutine that executes the callable in the background.
 
     This helper makes it easier to call functions that can not be