[clock] Add a centralised Clock, responsible for anything related to …

…time

This makes time quite easier to mock during integration tests :-)

pyproject.toml

@@ -49,7 +49,7 @@ includes = "src"
 asyncio_mode = "auto"
 testpaths = ["tests"]
 markers = [
-    "integration_test: marks tests as slow integration tests(deselect with '-m \"not integration_test\"')",
+    "integration_test: marks tests as slow integration tests (deselect with '-m \"not integration_test\"')",
 ]
 
 [build-system]

sandbox/scroll_to_widget.py

@@ -35,7 +35,7 @@ class Introduction(Widget):
     }
     """
 
-    def render(self) -> RenderableType:
+    def render(self, styles) -> RenderableType:
         return Text(
             "Press keys 0 to 9 to scroll to the Placeholder with that ID.",
             justify="center",

src/textual/_animator.py

@@ -7,6 +7,7 @@
 
 from dataclasses import dataclass
 
+from . import _clock
 from ._easing import DEFAULT_EASING, EASING
 from ._timer import Timer
 from ._types import MessageTarget
@@ -179,9 +180,9 @@ def animate(
             raise AttributeError(
                 f"Can't animate attribute {attribute!r} on {obj!r}; attribute does not exist"
             )
-        assert not all(
-            (duration, speed)
-        ), "An Animation should have a duration OR a speed, received both"
+        assert (duration is not None and speed is None) or (
+            duration is None and speed is not None
+        ), "An Animation should have a duration OR a speed"
 
         if final_value is ...:
             final_value = value
@@ -247,4 +248,4 @@ def _get_time(self) -> float:
         """Get the current wall clock time, via the internal Timer."""
         # N.B. We could remove this method and always call `self._timer.get_time()` internally,
         # but it's handy to have in mocking situations
-        return self._timer.get_time()
+        return _clock.get_time()

src/textual/_clock.py

@@ -0,0 +1,58 @@
+import asyncio
+from time import monotonic
+
+
+"""
+A module that serves as the single source of truth for everything time-related in a Textual app.
+Having this logic centralised makes it easier to simulate time in integration tests, 
+by mocking the few functions exposed by this module.
+"""
+
+
+# N.B. This class and its singleton instance have to be hidden APIs because we want to be able to mock time,
+# even for Python modules that imported functions such as `get_time` *before* we mocked this internal _Clock.
+# (so mocking public APIs such as `get_time` wouldn't affect direct references to then that were done during imports)
+class _Clock:
+    def get_time(self) -> float:
+        return monotonic()
+
+    async def aget_time(self) -> float:
+        return self.get_time()
+
+    async def sleep(self, seconds: float) -> None:
+        await asyncio.sleep(seconds)
+
+
+# That's our target for mocking time! :-)
+_clock = _Clock()
+
+
+def get_time() -> float:
+    """
+    Get the current wall clock time.
+
+    Returns:
+        float: the value (in fractional seconds) of a monotonic clock, i.e. a clock that cannot go backwards.
+    """
+    return _clock.get_time()
+
+
+async def aget_time() -> float:
+    """
+    Asynchronous version of `get_time`. Useful in situations where we want asyncio to be
+    able to "do things" elsewhere right before we fetch the time.
+
+    Returns:
+        float: the value (in fractional seconds) of a monotonic clock, i.e. a clock that cannot go backwards.
+    """
+    return await _clock.aget_time()
+
+
+async def sleep(seconds: float) -> None:
+    """
+    Coroutine that completes after a given time (in seconds).
+
+    Args:
+        seconds (float): the duration we should wait for before unblocking the awaiter
+    """
+    return await _clock.sleep(seconds)

src/textual/_timer.py

@@ -5,23 +5,19 @@
 from asyncio import (
     CancelledError,
     Event,
-    sleep,
     Task,
 )
-from time import monotonic
 from typing import Awaitable, Callable, Union
 
 from rich.repr import Result, rich_repr
 
 from . import events
 from ._callback import invoke
+from . import _clock
 from ._types import MessageTarget
 
 TimerCallback = Union[Callable[[], Awaitable[None]], Callable[[], None]]
 
-# /!\ This should only be changed in an "integration tests" context, in which we mock time
-_TIMERS_CAN_SKIP: bool = True
-
 
 class EventTargetGone(Exception):
     pass
@@ -106,32 +102,23 @@ def resume(self) -> None:
         """Result a paused timer."""
         self._active.set()
 
-    @staticmethod
-    def get_time() -> float:
-        """Get the current wall clock time."""
-        # N.B. This method will likely be a mocking target in integration tests.
-        return monotonic()
-
-    @staticmethod
-    async def _sleep(duration: float) -> None:
-        # N.B. This method will likely be a mocking target in integration tests.
-        await sleep(duration)
-
     async def _run(self) -> None:
         """Run the timer."""
         count = 0
         _repeat = self._repeat
         _interval = self._interval
-        start = self.get_time()
+        start = await _clock.aget_time()
         try:
             while _repeat is None or count <= _repeat:
                 next_timer = start + ((count + 1) * _interval)
-                if self._skip and _TIMERS_CAN_SKIP and next_timer < self.get_time():
+                now = await _clock.aget_time()
+                if self._skip and next_timer < now:
                     count += 1
                     continue
-                wait_time = max(0, next_timer - self.get_time())
+                now = await _clock.aget_time()
+                wait_time = max(0, next_timer - now)
                 if wait_time:
-                    await self._sleep(wait_time)
+                    await _clock.sleep(wait_time)
                 count += 1
                 try:
                     await self._tick(next_timer=next_timer, count=count)

src/textual/message.py

@@ -1,10 +1,10 @@
 from __future__ import annotations
 
-from time import monotonic
 from typing import ClassVar
 
 import rich.repr
 
+from . import _clock
 from .case import camel_to_snake
 from ._types import MessageTarget
 
@@ -39,7 +39,7 @@ def __init__(self, sender: MessageTarget) -> None:
 
         self.sender = sender
         self.name = camel_to_snake(self.__class__.__name__.replace("Message", ""))
-        self.time = self._get_time()
+        self.time = _clock.get_time()
         self._forwarded = False
         self._no_default_action = False
         self._stop_propagation = False
@@ -99,9 +99,3 @@ def stop(self, stop: bool = True) -> Message:
         """
         self._stop_propagation = stop
         return self
-
-    @staticmethod
-    def _get_time() -> float:
-        """Get the current wall clock time."""
-        # N.B. This method will likely be a mocking target in integration tests.
-        return monotonic()