However, I’ve found that pure Ada code without a package manager is pretty easy to integrate using the gprbuild tool; you just copy the dependency’s .ads and .adb files into your project and add their enclosing folder to the list of source directories. gprbuild figures our how to build them pretty much automatically.
So I wish that instead of using TOML files, the dependencies would be specified in the gprbuild project files themselves. The syntax/options of GPR files would probably have to be extended, but it would be nice to have only one layer of config files that contains everything needed to build an Ada library/project.