Integration of Clang-Tidy into CI

Notes

• Developer codes should be updated from up to date commit on master 602b6715 (I merged into Fix-CI-testjobs branch to avoid headaches with clang-tidy discovering new problems once merged into master)
• Updates not deployed to homeworks yet!

The pipeline now

• Async. jobs according to dependency graph
• Total pipeline takes about 30min max

Clang-Tidy

• Custom list of checks that I deemed useful
• Some checks had to be left out due to many false positives (e.g. const correctness) or because they didn't play well with Eigen
• Treat warnings as errors:
  • Pro: Forces developers to handle warnings, otherwise we may just get a sea of warnings some months down the line that nobody bothers to sift through anymore
  • Con: Future developers will be forced to sometimes add // NOLINT(<check>) to handle erroneous warnings (e.g. variables only used in assert-like statements are viewed as unused parameters!)
• Only developers folder is checked! I left out lecturecodes as I deemed them less important to check (though I could add them)
• LLVM's parallel clang-tidy script can also apply autofixes but I've found it to be a little buggy unfortunately. It can do parallelized checks for the pipeline though.

Overall clang-tidy discovered useful problems imo, e.g. inconsistent variable names between function declarations and definitions.

Custom check for std::system calls

Since clang-tidy doesn't allow creating custom checks in a simple way, I just created a bash script that returns an error if it finds a std::system call within the developers folder. It also shows where it found it. (Recall that we want to forbid std::system as it throws no error when the system call fails so a pipeline would still pass. We have a wrapper function that takes care of this now)