homebrew: how to tell if a formula is binary How do I tell if a particular formula will be installed as binary of from source?

Is there a brew command for this?
You could use brew edit ${formula_name}. That will open an editor with the formula contents. If there is a reference to a "bottle", then installing it with default settings will use that. 
However, if you add an option, then homebrew will compile the software for you.