Building gcc with --HEAD results in most of the executables not having a
version suffix, e.g. Building/installing gcc 6 would result in gcc-6,
g++-6, etc. being installed, while building/installing gcc --HEAD would
result in gcc-, g++-, etc. being installed.
The lack of a version suffix prevented brew from recognizing a valid gcc
install, resulting in brew instructing users to install gcc before
building certain formulae even though gcc is installed.
A patch to the gcc formula makes the version number for --HEAD builds
the major version number of the stable version + 1 (7 at this time).
This patch teaches brew to recognize current --HEAD builds as valid
compilers.
This is the (partially) documented public API for Homebrew.
The main class you should look at is the {Formula} class (and classes linked from there). That's the class that's used to create Homebrew formulae (i.e. package descriptions). Assume anything else you stumble upon is private.
Alex Wang
4cec6f5dd0