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Disallow absolute deadlines for relative cancel scopes #3403

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3 changes: 3 additions & 0 deletions newsfragments/3403.deprecated.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Trying to use absolute deadlines on a `trio.CancelScope` constructed
with a relative deadline now raises, after being deprecated since Trio
0.27.0.
Comment on lines +1 to +3
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@CoolCat467 CoolCat467 Mar 3, 2026

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Maybe have a small snippet about how to port old code if this wasn't already mentioned in 0.27.0's release notes, though I wouldn't expect many people to encounter that since it's been depreciated for quite a bit now.

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@jakkdl jakkdl Mar 5, 2026

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The correct solution is to create a new CancelScope, or calculate what the relative time would be with the help of trio.current_time(), or often simply just simplifying code that previously needlessly set absolute deadlines with cs.deadline = trio.current_time() + 5.
But I think the resolutions are varied and simple enough that it's not worth trying to cater too much to it.

20 changes: 6 additions & 14 deletions src/trio/_core/_run.py
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Expand Up @@ -808,13 +808,9 @@ def deadline(self) -> float:
"""
if self._relative_deadline != inf:
assert self._deadline == inf
warnings.warn(
DeprecationWarning(
"unentered relative cancel scope does not have an absolute deadline. Use `.relative_deadline`",
),
stacklevel=2,
raise RuntimeError(
"Unentered relative cancel scope does not have an absolute deadline."
)
return current_time() + self._relative_deadline
return self._deadline

@deadline.setter
Expand All @@ -823,13 +819,9 @@ def deadline(self, new_deadline: float) -> None:
raise ValueError("deadline must not be NaN")
if self._relative_deadline != inf:
assert self._deadline == inf
warnings.warn(
DeprecationWarning(
"unentered relative cancel scope does not have an absolute deadline. Transforming into an absolute cancel scope. First set `.relative_deadline = math.inf` if you do want an absolute cancel scope.",
),
stacklevel=2,
raise RuntimeError(
"Unentered relative cancel scope does not have an absolute deadline."
)
self._relative_deadline = inf
with self._might_change_registered_deadline():
self._deadline = float(new_deadline)

Expand All @@ -852,7 +844,7 @@ def relative_deadline(self) -> float:
elif self._deadline != inf:
assert self._relative_deadline == inf
raise RuntimeError(
"unentered non-relative cancel scope does not have a relative deadline",
"Unentered non-relative cancel scope does not have a relative deadline",
)
return self._relative_deadline

Expand All @@ -868,7 +860,7 @@ def relative_deadline(self, new_relative_deadline: float) -> None:
elif self._deadline != inf:
assert self._relative_deadline == inf
raise RuntimeError(
"unentered non-relative cancel scope does not have a relative deadline",
"Unentered non-relative cancel scope does not have a relative deadline",
)
else:
self._relative_deadline = new_relative_deadline
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22 changes: 9 additions & 13 deletions src/trio/_tests/test_timeouts.py
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Expand Up @@ -246,26 +246,22 @@ async def test_timeout_deadline_on_entry(mock_clock: _core.MockClock) -> None:
async def test_invalid_access_unentered(mock_clock: _core.MockClock) -> None:
cs = move_on_after(5)
mock_clock.jump(3)
start = _core.current_time()

match_str = "^unentered relative cancel scope does not have an absolute deadline"
with pytest.warns(DeprecationWarning, match=match_str):
assert cs.deadline == start + 5
mock_clock.jump(1)
# this is hella sketchy, but they *have* been warned
with pytest.warns(DeprecationWarning, match=match_str):
assert cs.deadline == start + 6
match_str = "^Unentered relative cancel scope does not have an absolute deadline"
with pytest.raises(RuntimeError, match=match_str):
print("SHOULD NOT PRINT! deadline:", cs.deadline)
Comment on lines +251 to +252
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@jakkdl jakkdl Mar 5, 2026

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Suggested change
with pytest.raises(RuntimeError, match=match_str):
print("SHOULD NOT PRINT! deadline:", cs.deadline)
with pytest.raises(RuntimeError, match=match_str):
cs.deadline

no need for the print, no?


with pytest.warns(DeprecationWarning, match=match_str):
with pytest.raises(RuntimeError, match=match_str):
cs.deadline = 7
# now transformed into absolute
assert cs.deadline == 7
assert not cs.is_relative

# nothing happened!
assert cs.relative_deadline == 5
assert cs.is_relative

cs = move_on_at(5)

match_str = (
"^unentered non-relative cancel scope does not have a relative deadline$"
"^Unentered non-relative cancel scope does not have a relative deadline$"
)
with pytest.raises(RuntimeError, match=match_str):
assert cs.relative_deadline
Expand Down