using sub builds with file API

When using the file API for ide integration is it possible to create a build per project for Makefile generators?

I would like to create a sub project from my main build by using a second project call.

No, there’s no functionality for that.

is there a way to add it? I found a bug in Sublime Text generator. Instead of fixing it i thought about using file API, since it provides a lot more configuration features.

I don’t think that kind of thing is likely to happen anytime soon. There are probably a decent amount of behavioral changes to making any project call change things like this.