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Ignore import errors in API URLs check

Erwan Rouchet requested to merge explicit-import-errors into master

While working on !1923 (merged), I shuffled some serializers around as they were in the wrong file. I expected to be able to fix the imports by just letting pre-commit cry, then letting manage.py runserver cry, but instead I got this:

λ ./manage.py runserver
2023-02-21 14:07:23,297 [INFO] Watching for file changes with StatReloader
Performing system checks...

Exception in thread django-main-thread:
Traceback (most recent call last):
  File "/usr/lib/python3.8/threading.py", line 932, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.8/threading.py", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "/home/lucidiot/.virtualenvs/backend/lib/python3.8/site-packages/django/utils/autoreload.py", line 64, in wrapper
    fn(*args, **kwargs)
  File "/home/lucidiot/.virtualenvs/backend/lib/python3.8/site-packages/django/core/management/commands/runserver.py", line 134, in inner_run
    self.check(display_num_errors=True)
  File "/home/lucidiot/.virtualenvs/backend/lib/python3.8/site-packages/django/core/management/base.py", line 475, in check
    all_issues = checks.run_checks(
  File "/home/lucidiot/.virtualenvs/backend/lib/python3.8/site-packages/django/core/checks/registry.py", line 88, in run_checks
    new_errors = check(app_configs=app_configs, databases=databases)
  File "/home/lucidiot/dev/ark/backend/arkindex/project/checks.py", line 41, in api_urls_check
    from arkindex.project.api_v1 import api
ImportError: cannot import name 'api' from 'arkindex.project.api_v1' (/home/lucidiot/dev/ark/backend/arkindex/project/api_v1.py)

There was nothing wrong in arkindex.project.checks or in arkindex.project.api_v1 though! I had some import errors in arkindex.documents.serializers.entities instead.

This non-explicit error only occurs when you are importing from a module that does exist, but importing something that doesn't, for example from arkindex import beer (sadly). Importing from a module that does not exist results in a ModuleNotFoundError that will show the proper stack trace.

Handling the ImportError when the API URLs check tries to import api_v1 to check the URLs allows Django to continue to load after running the system checks, which will end up making it crash once more with the real ImportError, showing the proper stack trace that points at the real import issue.

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