Fix CapacityLimiter._pending_borrowers leak on non-Cancelled exceptions

[bysiber]

Problem

CapacityLimiter.acquire_on_behalf_of only cleans up _pending_borrowers when park() raises trio.Cancelled. If park() raises any other exception — such as KeyboardInterrupt delivered to a parked task via the abort mechanism — the task's entry stays in _pending_borrowers permanently.

The relevant code:

try:
    await self._lot.park()
except trio.Cancelled:
    self._pending_borrowers.pop(task)
    raise

When KeyboardInterrupt is delivered to the task, the abort function succeeds and the task is rescheduled with raise_cancel() which raises KeyboardInterrupt, not trio.Cancelled. The stale entry leaks.

Fix

Broadened the exception handler to BaseException and use pop(task, None) for safety against double-removal:

except BaseException:
    self._pending_borrowers.pop(task, None)
    raise

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00000%. Comparing base (2fd138e) to head (16ec20f).

Additional details and impacted files

@@               Coverage Diff               @@
##                 main        #3399   +/-   ##
===============================================
  Coverage   100.00000%   100.00000%           
===============================================
  Files             128          128           
  Lines           19424        19424           
  Branches         1318         1318           
===============================================
  Hits            19424        19424           

Files with missing lines	Coverage Δ
src/trio/_sync.py	100.00000% <100.00000%> (ø)

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[A5rocks]

Please create an issue before fixing bugs like this. I'm fairly certain this is not actually an issue, so I will be closing this. I'd be happy to reopen this though.

[A5rocks]

KI cannot be raised here because we are in a @enable_ki_protection function.