Add clang-tidy CI workflow

[giacomofiorin]

In draft for now: even with the default settings, the current code does not pass the test.

[giacomofiorin]

@HanatoK Continuing the conversation here, one of the advantages of using a container is to use a recent version of the Clang tools. The ubuntu-latest GitHub instance runs 18, but CentOS 9 comes with version 20.

[giacomofiorin]

With the downgrade from Clang 20 to 18 and removal of the Lepton sources, we are down to two issues, one with colvarproxy_io::io_available() and one with the bitwise OR of values of Parse_Mode type.

I have a good idea about how to fix the former (requires some small refactoring) but I'm puzzled by the latter: I though that having added the clang::flag_enum annotation would have taken care of it, but was wrong. Any ideas?

[giacomofiorin]

Looks like the checks are the same between 18 and 20, but good to have the latter back for the future (thanks @HanatoK).

I would like to add support for GNU Parallel in run_clang_tidy.sh. (The original command run-clang-tidy had the advantage of a -j flag.) What do you think?

[HanatoK]

Looks like the checks are the same between 18 and 20, but good to have the latter back for the future (thanks @HanatoK).

I would like to add support for GNU Parallel in run_clang_tidy.sh. (The original command run-clang-tidy had the advantage of a -j flag.) What do you think?

That's a good idea, but I don't know how to parallelize the script with GNU Parallel. It looks like there are other ways to parallelize the executions as well (see https://stackoverflow.com/questions/38774355/how-to-parallelize-for-loop-in-bash-limiting-number-of-processes).

[giacomofiorin]

That's a good idea, but I don't know how to parallelize the script with GNU Parallel. It looks like there are other ways to parallelize the executions as well (see https://stackoverflow.com/questions/38774355/how-to-parallelize-for-loop-in-bash-limiting-number-of-processes).

I had forgotten about xargs -P: it's less powerful than Parallel, but more widely available. I added it to the script.

Also restored the -header-filter flag, so that we can see warnings from headers (there's a bunch in colvar_UIestimator.h