Avoid creating closed futures that will never be awaited

[bdraco]

Summary

This PR is a follow-up to #11100 and #3733 that avoids creating closed futures in ResponseHandler that will never be awaited, preventing spurious "Future exception was never retrieved" warnings.

Changes

Lazy Creation of Closed Future

• Changed ResponseHandler.closed from eagerly creating a future in __init__ to lazily creating it only when accessed
• The future is only created if the connection hasn't already been lost
• Returns None if connection_lost() was called before the property was ever accessed

Connector Updates

• Updated BaseConnector.close() to check if proto.closed is not None before adding it to waiters
• This prevents waiting on futures that don't exist

Benefits

1. Performance: Avoids creating futures for connections that close immediately or are never awaited
2. Cleaner Logs: Prevents "Future exception was never retrieved" warnings for futures that were never needed without having to manually suppress them
3. Memory: Reduces memory usage by not creating unnecessary future objects

Testing

The changes include comprehensive test coverage to ensure:

• Lazy creation works correctly
• Backward compatibility is maintained
• The connector properly handles None closed futures
• Exception handling still works when the future is created

Related Issues

• Follows up on Fix spurious "Future exception was never retrieved" warnings for connection lost errors #11100 (Fix spurious warnings for connection lost errors)
• Related to Fix closing client session #3733 (Previous work on connection handling)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.83%. Comparing base (3a2a9b2) to head (1bce36f).
Report is 2 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #11107   +/-   ##
=======================================
  Coverage   98.82%   98.83%           
=======================================
  Files         129      129           
  Lines       41505    41542   +37     
  Branches     2234     2238    +4     
=======================================
+ Hits        41019    41056   +37     
  Misses        337      337           
  Partials      149      149           

Flag	Coverage Δ
CI-GHA	98.71% <100.00%> (+<0.01%)	⬆️
OS-Linux	98.43% <100.00%> (+<0.01%)	⬆️
OS-Windows	96.69% <100.00%> (-0.02%)	⬇️
OS-macOS	97.62% <100.00%> (-0.01%)	⬇️
Py-3.10.11	97.38% <100.00%> (-0.01%)	⬇️
Py-3.10.17	97.89% <100.00%> (-0.02%)	⬇️
Py-3.11.12	98.06% <100.00%> (-0.01%)	⬇️
Py-3.11.9	97.56% <100.00%> (+<0.01%)	⬆️
Py-3.12.10	98.46% <100.00%> (+<0.01%)	⬆️
Py-3.13.3	98.44% <100.00%> (+<0.01%)	⬆️
Py-3.9.13	97.27% <100.00%> (-0.01%)	⬇️
Py-3.9.22	97.77% <100.00%> (-0.01%)	⬇️
Py-pypy7.3.16	83.15% <100.00%> (-10.26%)	⬇️
VM-macos	97.62% <100.00%> (-0.01%)	⬇️
VM-ubuntu	98.43% <100.00%> (+<0.01%)	⬆️
VM-windows	96.69% <100.00%> (-0.02%)	⬇️

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[codspeed-hq]

CodSpeed Performance Report

Merging #11107 will not alter performance

_{Comparing future_no_need (1bce36f) with master (3a2a9b2)}

Summary

✅ 59 untouched benchmarks

[patchback]

Backport to 3.12: 💔 cherry-picking failed — conflicts found

❌ Failed to cleanly apply 21d640d on top of patchback/backports/3.12/21d640dc4b046be18bcb42aad8fa5445198fd219/pr-11107

Backporting merged PR #11107 into master

1. Ensure you have a local repo clone of your fork. Unless you cloned it
   from the upstream, this would be your origin remote.
2. Make sure you have an upstream repo added as a remote too. In these
   instructions you'll refer to it by the name upstream. If you don't
   have it, here's how you can add it:

   $ git remote add upstream https://github.com/aio-libs/aiohttp.git

3. Ensure you have the latest copy of upstream and prepare a branch
   that will hold the backported code:

   $ git fetch upstream
   $ git checkout -b patchback/backports/3.12/21d640dc4b046be18bcb42aad8fa5445198fd219/pr-11107 upstream/3.12

4. Now, cherry-pick PR Avoid creating closed futures that will never be awaited #11107 contents into that branch:

   $ git cherry-pick -x 21d640dc4b046be18bcb42aad8fa5445198fd219

   If it'll yell at you with something like fatal: Commit 21d640dc4b046be18bcb42aad8fa5445198fd219 is a merge but no -m option was given., add -m 1 as follows instead:

   $ git cherry-pick -m1 -x 21d640dc4b046be18bcb42aad8fa5445198fd219

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR Avoid creating closed futures that will never be awaited #11107 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/3.12/21d640dc4b046be18bcb42aad8fa5445198fd219/pr-11107

7. Create a PR, ensure that the CI is green. If it's not — update it so that
   the tests and any other checks pass. This is it!
   Now relax and wait for the maintainers to process your pull request
   when they have some cycles to do reviews. Don't worry — they'll tell you if
   any improvements are necessary when the time comes!

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 3.13: 💔 cherry-picking failed — conflicts found

❌ Failed to cleanly apply 21d640d on top of patchback/backports/3.13/21d640dc4b046be18bcb42aad8fa5445198fd219/pr-11107

Backporting merged PR #11107 into master

1. Ensure you have a local repo clone of your fork. Unless you cloned it
   from the upstream, this would be your origin remote.
2. Make sure you have an upstream repo added as a remote too. In these
   instructions you'll refer to it by the name upstream. If you don't
   have it, here's how you can add it:

   $ git remote add upstream https://github.com/aio-libs/aiohttp.git

3. Ensure you have the latest copy of upstream and prepare a branch
   that will hold the backported code:

   $ git fetch upstream
   $ git checkout -b patchback/backports/3.13/21d640dc4b046be18bcb42aad8fa5445198fd219/pr-11107 upstream/3.13

4. Now, cherry-pick PR Avoid creating closed futures that will never be awaited #11107 contents into that branch:

   $ git cherry-pick -x 21d640dc4b046be18bcb42aad8fa5445198fd219

   If it'll yell at you with something like fatal: Commit 21d640dc4b046be18bcb42aad8fa5445198fd219 is a merge but no -m option was given., add -m 1 as follows instead:

   $ git cherry-pick -m1 -x 21d640dc4b046be18bcb42aad8fa5445198fd219

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR Avoid creating closed futures that will never be awaited #11107 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/3.13/21d640dc4b046be18bcb42aad8fa5445198fd219/pr-11107

7. Create a PR, ensure that the CI is green. If it's not — update it so that
   the tests and any other checks pass. This is it!
   Now relax and wait for the maintainers to process your pull request
   when they have some cycles to do reviews. Don't worry — they'll tell you if
   any improvements are necessary when the time comes!

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.