> In this specific example, I saw that building the project required mucking with my rust version/setup and decided that the cost of that was too high for me to proceed.

Agreed it would be nice if you could compile it with your package manager's provided version of rust.

Sibling comments mentioned rustup; with it this is the entirety of the mucking required [as described by alacritty's readme, and confirmed by compiling it myself]:

    rustup override set $(cat rustc-version)

The override is local to the project of the directory you set it in. This will also download that version of rust if necessary.