(I say you are in luck because I happen to have been working on that part of the code recently) Pants targets accept an option “compiler_option_sets”, so you are looking to add something like

compiler_option_sets = {"fatal_warnings"}

to the targets that have to have them enabled

@brief-engineer-67497: Dorothy has a PR out to add some docs for that here: https://github.com/pantsbuild/pants/pull/6595

nice ! thanks