Add missing type hints to `synapse.logging.context` (#11556)

1 files changed, 103 insertions, 46 deletions

diff --git a/synapse/logging/context.py b/synapse/logging/context.py
index d8ae3188b7..25e78cc82f 100644
--- a/synapse/logging/context.py
+++ b/synapse/logging/context.py
@@ -22,20 +22,33 @@ them.
 
 See doc/log_contexts.rst for details on how this works.
 """
-import inspect
 import logging
 import threading
 import typing
 import warnings
-from typing import TYPE_CHECKING, Optional, Tuple, TypeVar, Union
+from types import TracebackType
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Awaitable,
+    Callable,
+    Optional,
+    Tuple,
+    Type,
+    TypeVar,
+    Union,
+    overload,
+)
 
 import attr
 from typing_extensions import Literal
 
 from twisted.internet import defer, threads
+from twisted.python.threadpool import ThreadPool
 
 if TYPE_CHECKING:
     from synapse.logging.scopecontextmanager import _LogContextScope
+    from synapse.types import ISynapseReactor
 
 logger = logging.getLogger(__name__)
 
@@ -66,7 +79,7 @@ except Exception:
 
 
 # a hook which can be set during testing to assert that we aren't abusing logcontexts.
-def logcontext_error(msg: str):
+def logcontext_error(msg: str) -> None:
     logger.warning(msg)
 
 
@@ -223,22 +236,19 @@ class _Sentinel:
     def __str__(self) -> str:
         return "sentinel"
 
-    def copy_to(self, record):
-        pass
-
-    def start(self, rusage: "Optional[resource.struct_rusage]"):
+    def start(self, rusage: "Optional[resource.struct_rusage]") -> None:
         pass
 
-    def stop(self, rusage: "Optional[resource.struct_rusage]"):
+    def stop(self, rusage: "Optional[resource.struct_rusage]") -> None:
         pass
 
-    def add_database_transaction(self, duration_sec):
+    def add_database_transaction(self, duration_sec: float) -> None:
         pass
 
-    def add_database_scheduled(self, sched_sec):
+    def add_database_scheduled(self, sched_sec: float) -> None:
         pass
 
-    def record_event_fetch(self, event_count):
+    def record_event_fetch(self, event_count: int) -> None:
         pass
 
     def __bool__(self) -> Literal[False]:
@@ -379,7 +389,12 @@ class LoggingContext:
             )
         return self
 
-    def __exit__(self, type, value, traceback) -> None:
+    def __exit__(
+        self,
+        type: Optional[Type[BaseException]],
+        value: Optional[BaseException],
+        traceback: Optional[TracebackType],
+    ) -> None:
         """Restore the logging context in thread local storage to the state it
         was before this context was entered.
         Returns:
@@ -399,17 +414,6 @@ class LoggingContext:
         # recorded against the correct metrics.
         self.finished = True
 
-    def copy_to(self, record) -> None:
-        """Copy logging fields from this context to a log record or
-        another LoggingContext
-        """
-
-        # we track the current request
-        record.request = self.request
-
-        # we also track the current scope:
-        record.scope = self.scope
-
     def start(self, rusage: "Optional[resource.struct_rusage]") -> None:
         """
         Record that this logcontext is currently running.
@@ -626,7 +630,12 @@ class PreserveLoggingContext:
     def __enter__(self) -> None:
         self._old_context = set_current_context(self._new_context)
 
-    def __exit__(self, type, value, traceback) -> None:
+    def __exit__(
+        self,
+        type: Optional[Type[BaseException]],
+        value: Optional[BaseException],
+        traceback: Optional[TracebackType],
+    ) -> None:
         context = set_current_context(self._old_context)
 
         if context != self._new_context:
@@ -711,16 +720,61 @@ def nested_logging_context(suffix: str) -> LoggingContext:
     )
 
 
-def preserve_fn(f):
+R = TypeVar("R")
+
+
+@overload
+def preserve_fn(  # type: ignore[misc]
+    f: Callable[..., Awaitable[R]],
+) -> Callable[..., "defer.Deferred[R]"]:
+    # The `type: ignore[misc]` above suppresses
+    # "Overloaded function signatures 1 and 2 overlap with incompatible return types"
+    ...
+
+
+@overload
+def preserve_fn(f: Callable[..., R]) -> Callable[..., "defer.Deferred[R]"]:
+    ...
+
+
+def preserve_fn(
+    f: Union[
+        Callable[..., R],
+        Callable[..., Awaitable[R]],
+    ]
+) -> Callable[..., "defer.Deferred[R]"]:
     """Function decorator which wraps the function with run_in_background"""
 
-    def g(*args, **kwargs):
+    def g(*args: Any, **kwargs: Any) -> "defer.Deferred[R]":
         return run_in_background(f, *args, **kwargs)
 
     return g
 
 
-def run_in_background(f, *args, **kwargs) -> defer.Deferred:
+@overload
+def run_in_background(  # type: ignore[misc]
+    f: Callable[..., Awaitable[R]], *args: Any, **kwargs: Any
+) -> "defer.Deferred[R]":
+    # The `type: ignore[misc]` above suppresses
+    # "Overloaded function signatures 1 and 2 overlap with incompatible return types"
+    ...
+
+
+@overload
+def run_in_background(
+    f: Callable[..., R], *args: Any, **kwargs: Any
+) -> "defer.Deferred[R]":
+    ...
+
+
+def run_in_background(
+    f: Union[
+        Callable[..., R],
+        Callable[..., Awaitable[R]],
+    ],
+    *args: Any,
+    **kwargs: Any,
+) -> "defer.Deferred[R]":
     """Calls a function, ensuring that the current context is restored after
     return from the function, and that the sentinel context is set once the
     deferred returned by the function completes.
@@ -751,6 +805,10 @@ def run_in_background(f, *args, **kwargs) -> defer.Deferred:
     # At this point we should have a Deferred, if not then f was a synchronous
     # function, wrap it in a Deferred for consistency.
     if not isinstance(res, defer.Deferred):
+        # `res` is not a `Deferred` and not a `Coroutine`.
+        # There are no other types of `Awaitable`s we expect to encounter in Synapse.
+        assert not isinstance(res, Awaitable)
+
         return defer.succeed(res)
 
     if res.called and not res.paused:
@@ -778,13 +836,14 @@ def run_in_background(f, *args, **kwargs) -> defer.Deferred:
     return res
 
 
-def make_deferred_yieldable(deferred):
-    """Given a deferred (or coroutine), make it follow the Synapse logcontext
-    rules:
+T = TypeVar("T")
+
 
-    If the deferred has completed (or is not actually a Deferred), essentially
-    does nothing (just returns another completed deferred with the
-    result/failure).
+def make_deferred_yieldable(deferred: "defer.Deferred[T]") -> "defer.Deferred[T]":
+    """Given a deferred, make it follow the Synapse logcontext rules:
+
+    If the deferred has completed, essentially does nothing (just returns another
+    completed deferred with the result/failure).
 
     If the deferred has not yet completed, resets the logcontext before
     returning a deferred. Then, when the deferred completes, restores the
@@ -792,16 +851,6 @@ def make_deferred_yieldable(deferred):
 
     (This is more-or-less the opposite operation to run_in_background.)
     """
-    if inspect.isawaitable(deferred):
-        # If we're given a coroutine we convert it to a deferred so that we
-        # run it and find out if it immediately finishes, it it does then we
-        # don't need to fiddle with log contexts at all and can return
-        # immediately.
-        deferred = defer.ensureDeferred(deferred)
-
-    if not isinstance(deferred, defer.Deferred):
-        return deferred
-
     if deferred.called and not deferred.paused:
         # it looks like this deferred is ready to run any callbacks we give it
         # immediately. We may as well optimise out the logcontext faffery.
@@ -823,7 +872,9 @@ def _set_context_cb(result: ResultT, context: LoggingContext) -> ResultT:
     return result
 
 
-def defer_to_thread(reactor, f, *args, **kwargs):
+def defer_to_thread(
+    reactor: "ISynapseReactor", f: Callable[..., R], *args: Any, **kwargs: Any
+) -> "defer.Deferred[R]":
     """
     Calls the function `f` using a thread from the reactor's default threadpool and
     returns the result as a Deferred.
@@ -855,7 +906,13 @@ def defer_to_thread(reactor, f, *args, **kwargs):
     return defer_to_threadpool(reactor, reactor.getThreadPool(), f, *args, **kwargs)
 
 
-def defer_to_threadpool(reactor, threadpool, f, *args, **kwargs):
+def defer_to_threadpool(
+    reactor: "ISynapseReactor",
+    threadpool: ThreadPool,
+    f: Callable[..., R],
+    *args: Any,
+    **kwargs: Any,
+) -> "defer.Deferred[R]":
     """
     A wrapper for twisted.internet.threads.deferToThreadpool, which handles
     logcontexts correctly.
@@ -897,7 +954,7 @@ def defer_to_threadpool(reactor, threadpool, f, *args, **kwargs):
         assert isinstance(curr_context, LoggingContext)
         parent_context = curr_context
 
-    def g():
+    def g() -> R:
         with LoggingContext(str(curr_context), parent_context=parent_context):
             return f(*args, **kwargs)