When CircleCI started, we manually set up customers' builds for them. They'd give us access to the code, and we'd look through their codebase to figure out how

When CircleCI started, we manually set up customers' builds for them. They'd give us access to the code, and we'd look through their codebase to figure out how to build the thing. Each new customer we'd add their rules to our "inference engine" (eg if you have a dir called vendor/bundle, you need to pass the --vendor flag to bundler). After about 20 customers it had gotten good enough that we could update it via support request instead.