Add check for missing or duplicate newlines at the end of files

[MaEtUgR]

Solved Problem

When checking changes I realized people do commit missing or duplicate newlines every now and then. This seems like a non-issue and only leads to problems later on when some tooling doesn't work because the files are not POSIX compliant or whitespace checks fail in the middle of a merge. Manual passes like #22476 end up not enforcing the rules.

Solution

• Add an automatic check for one single newline at the end of every file that is checked into the repository.

Changelog Entry

Style: Automate enforcing one single newline at the end of each file

Alternatives

Ideally, this would also run through with make format but I don't add it because I feel it adds too much delay and hence prolongs the pre-commit hook. Better to have it ran in CI than not at all but maybe someone knows how to make the check more efficient such that the runtime is insignificant during commits.

Test coverage

I tested locally that it triggers with:

• All the existing missing newlines and duplicate newlines
• Just one of the two checks
• Just one duplicate newline in a file

Context

Inspiration:

1. https://stackoverflow.com/a/54348931
2. https://stackoverflow.com/a/31829703/6326048

[MaEtUgR]

The check fails when not compliant: https://github.com/PX4/PX4-Autopilot/actions/runs/9191515223/job/25278084826?pr=23166

[MaEtUgR]

The check passes after the fixes

[MaEtUgR]

Hmm, e.g. SITL offboard, px4_fmu-v6xrt, MAVROS rover mission CI is also failing on main. There are quite some to look through 👀

[MaEtUgR]

I rebased the pr, this would have caught more newline issues since I opened the pr:

e.g. https://github.com/PX4/PX4-Autopilot/pull/22904/files#r1681278804

[DronecodeBot]

This pull request has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/px4-sync-q-a-july-17-2024/39749/1