Add type hints to twisted.internet.defer

.coveragerc

@@ -13,3 +13,6 @@ source=
 [report]
 precision = 2
 ignore_errors = True
+exclude_lines =
+    if TYPE_CHECKING
+    \s*\.\.\.$

mypy.ini

@@ -1,6 +1,6 @@
 [mypy]
 
-namespace_packages=True
+namespace_packages = True
 plugins=mypy_zope:plugin
 
 ignore_missing_imports = True
@@ -20,6 +20,18 @@ warn_return_any          = True
 warn_unreachable         = True
 warn_unused_ignores      = True
 
+# These are too strict for us at the moment
+
+disallow_any_decorated      = False
+disallow_any_explicit       = False
+disallow_any_expr           = False
+disallow_any_generics       = False
+disallow_any_unimported     = False
+disallow_subclassing_any    = False
+disallow_untyped_calls      = False
+disallow_untyped_decorators = False
+strict_equality             = False
+
 # Disable some checks until the effected modules fully adopt mypy
 
 [mypy-twisted._threads.*]
@@ -149,10 +161,6 @@ check_untyped_defs = False
 allow_untyped_defs = True
 check_untyped_defs = False
 
-[mypy-twisted.internet.defer]
-allow_untyped_defs = True
-check_untyped_defs = False
-
 [mypy-twisted.internet.endpoints]
 allow_untyped_defs = True
 check_untyped_defs = False

setup.cfg

@@ -32,6 +32,7 @@ install_requires =
     Automat >= 0.8.0
     hyperlink >= 17.1.1
     attrs >= 19.2.0
+    typing_extensions >= 3.6.5
     twisted-iocpsupport ~= 1.0.0; platform_system == "Windows"
 include_package_data = True
 zip_safe = False

src/twisted/application/twist/test/test_options.py

@@ -47,7 +47,7 @@ def patchOpen(self) -> None:
         """
         self.opened: List[Tuple[str, Optional[str]]] = []
 
-        def fakeOpen(name: str, mode: Optional[str] = None) -> object:
+        def fakeOpen(name: str, mode: Optional[str] = None) -> TextIO:
             if name == "nocanopen":
                 raise OSError(None, None, name)
 

src/twisted/internet/base.py

@@ -292,19 +292,21 @@ class ThreadedResolver:
 
     def __init__(self, reactor: "ReactorBase") -> None:
         self.reactor = reactor
-        self._runningQueries: Dict[Deferred, Tuple[Deferred, IDelayedCall]] = {}
+        self._runningQueries: Dict[
+            Deferred[str], Tuple[Deferred[str], IDelayedCall]
+        ] = {}
 
     def _fail(self, name: str, err: str) -> Failure:
         lookupError = error.DNSLookupError(f"address {name!r} not found: {err}")
         return Failure(lookupError)
 
-    def _cleanup(self, name: str, lookupDeferred: Deferred) -> None:
+    def _cleanup(self, name: str, lookupDeferred: Deferred[str]) -> None:
         userDeferred, cancelCall = self._runningQueries[lookupDeferred]
         del self._runningQueries[lookupDeferred]
         userDeferred.errback(self._fail(name, "timeout error"))
 
     def _checkTimeout(
-        self, result: object, name: str, lookupDeferred: Deferred
+        self, result: str, name: str, lookupDeferred: Deferred[str]
     ) -> None:
         try:
             userDeferred, cancelCall = self._runningQueries[lookupDeferred]
@@ -321,7 +323,7 @@ def _checkTimeout(
 
     def getHostByName(
         self, name: str, timeout: Sequence[int] = (1, 3, 11, 45)
-    ) -> Deferred:
+    ) -> Deferred[str]:
         """
         See L{twisted.internet.interfaces.IResolverSimple.getHostByName}.
 
@@ -333,7 +335,7 @@ def getHostByName(
             timeoutDelay = sum(timeout)
         else:
             timeoutDelay = 60
-        userDeferred = defer.Deferred()
+        userDeferred = defer.Deferred()  # type: Deferred[str]
         lookupDeferred = threads.deferToThreadPool(
             self.reactor,
             cast(IReactorThreads, self.reactor).getThreadPool(),
@@ -352,7 +354,7 @@ def getHostByName(
 class BlockingResolver:
     def getHostByName(
         self, name: str, timeout: Sequence[int] = (1, 3, 11, 45)
-    ) -> Deferred:
+    ) -> Deferred[str]:
         try:
             address = socket.gethostbyname(name)
         except OSError:
@@ -487,7 +489,7 @@ def fireEvent(self) -> None:
         """
         self.state = "BEFORE"
         self.finishedBefore = []
-        beforeResults: List[object] = []
+        beforeResults: List[Deferred[object]] = []
         while self.before:
             callable, args, kwargs = self.before.pop(0)
             self.finishedBefore.append((callable, args, kwargs))
@@ -691,7 +693,9 @@ def getWriters(self) -> List[IWriteDescriptor]:
         )
 
     # IReactorCore
-    def resolve(self, name: str, timeout: Sequence[int] = (1, 3, 11, 45)) -> Deferred:
+    def resolve(
+        self, name: str, timeout: Sequence[int] = (1, 3, 11, 45)
+    ) -> Deferred[str]:
         """
         Return a Deferred that will resolve a hostname."""
         if not name: