Here's a short writeup of a bit of my build system for a project I'm working on. It's pretty simple, and is just a relatively clean way of recording the repository state when code was compiled, so I can reproduce results later on. Just thought the interaction between git, cmake, and C++ was a bit nice!

Give Nix a look sometime, it takes this to a whole new level by including all of the build dependencies in the hash, and their build dependencies and so on. The standard flake workflow even includes the warning about having uncommitted files.

A simpler way to do this, especially if you do tagging in your repositories, is to use `git describe`. For example:

    $ git describe --dirty
    v1.4.1-1-gde18fe90-dirty

The format is <the most recent tag>-<the number of commits since that tag>-g<the short git hash>-<dirty, but only if the repo is dirty>.

If the repo isn't dirty, then the hash you get excludes that part:

    $ git describe --dirty
    v1.4.1-1-gde18fe90

If you're using lightweight tags (the default) and not annotated tags (with messages and signatures and etc) you may want to add `--tags` because otherwise it'll skip over any lightweight tags.

The other nice thing about this is that, if the repo is not -dirty, you can use the output from `git describe` in other git commands to reference that commit:

    $ git show -s v1.4.1-1-gde18fe90
    commit de18fe907edda2f2854e9813fcfbda9df902d8f1 (HEAD -> 1.4.1-release, origin/HEAD, origin/1.4.1-release)
    Author: rockowitz <rockowitz@minsoft.com>
    Date:   Sun May 28 17:09:46 2023 -0400

        Create codacy.yml