Ensure cleanup gets run.

[Dreamsorcerer]

This helps ensure that cleanup gets run, even when an exception occurs during startup. Fixes #4799

This becomes particularly painful when the server can't be cleanly restarted without the cleanup running, especially when running locally with aiohttp-devtools, where exceptions during development are likely, and cause the runserver command to break or lock up.

[codecov-commenter]

Codecov Report

Merging #4800 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4800      +/-   ##
==========================================
- Coverage   97.60%   97.60%   -0.01%     
==========================================
  Files          43       43              
  Lines        8932     8931       -1     
  Branches     1406     1406              
==========================================
- Hits         8718     8717       -1     
  Misses         95       95              
  Partials      119      119              

Impacted Files	Coverage Δ
aiohttp/web_runner.py	97.76% <ø> (-0.02%)	⬇️
aiohttp/web_app.py	97.32% <100.00%> (+0.01%)	⬆️

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[asvetlov]

I'm sorry but 'no'.
startup/cleanup works like try/finally block:

await startup()
try:
    await serve_http()
finally:
    await cleanup()

if startup call raises exception -- cleanup is not called.

[Dreamsorcerer]

@asvetlov I was thinking about tweaking this PR to only run parts with a cleanup context.

The problem I am encountering is that development is hard using the devtools, as whenever an exception occurs during startup, the application is left hanging and doesn't restart as it normally would.

It seems odd to me that a cleanup context would be left in an in-between state. The result is that e.g. a DB or other process doesn't get shut down due to an unrelated part of the application.