fix: don't exit on reload if there is a syntax error

[alsuren]

fixes #213

Now, if you introduce a syntax error, you immediately get:

 * Detected change in '/Users/david/src/opvia/app/scripts_v3/cloud_function/main.py', reloading
 * Restarting with watchdog (fsevents)
Traceback (most recent call last):
  File "/Users/david/src/opvia/app/.venv/lib/python3.10/site-packages/functions_framework/__init__.py", line 290, in create_app
    spec.loader.exec_module(source_module)
  File "<frozen importlib._bootstrap_external>", line 879, in exec_module
  File "<frozen importlib._bootstrap_external>", line 1017, in get_code
  File "<frozen importlib._bootstrap_external>", line 947, in source_to_code
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/Users/david/src/opvia/app/scripts_v3/cloud_function/main.py", line 11
    ///
    ^^
SyntaxError: invalid syntax
 * Debugger is active!
 * Debugger PIN: 104-682-644

and then if you curl your fuction endpoint, you get the debug html page for the syntax error, and the backtrace gets printed out to stderr again.

If you attempt to start the server when there is already a syntax error present, it correctly exits with the error, as before (the only difference being that the backtrace points at the raise e from None line rather than the spec.loader.exec_module(source_module) line).

This behaviour matches the upstream flask run behaviour now.

Feel free to be brutal about the quality of my python code: the last time I wrote significant production python, it was before python 2.7 was deprecated ;-)

[alsuren]

We are now using this patch both locally and in our cloud-function environment. We've not run into any issues with it yet.

What are the next steps for this?

[HKWinterhalter]

It looks like this will need test coverage and linting to pass

[alsuren]

python -m tox -e lint and python -m tox -e py-macos-latest pass locally (coverage is at 100%)

To work around the "This workflow requires approval from a maintainer" message, I made a PR against my own fork (alsuren#1). The 7 "Expected" checks seem to pass on that PR, so I'm confident that they should pass on this PR too.

I'm assuming that the other tests are not required, or just not configured correctly on my fork. Shout if you need me to look into any more issues.

[HKWinterhalter]

Thank you for fixing this @alsuren !