brew/Library/Homebrew/blacklist.rb

def blacklisted? name
  case name.downcase
  when /^vim?$/, 'screen', /^rubygems?$/ then <<-EOS.undent
    Apple distributes #{name} with OS X, you can find it in /usr/bin.
    EOS
  when 'libarchive', 'libpcap' then <<-EOS.undent
    Apple distributes #{name} with OS X, you can find it in /usr/lib.
    EOS
  when 'libiconv' then <<-EOS.undent
    Apple distributes #{name} with OS X, you can find it in /usr/lib.
    Some build scripts fail to detect it correctly, please check existing
    formulae for solutions.
    EOS
  when 'libxml', 'libxlst' then <<-EOS.undent
    Apple distributes #{name} with OS X, you can find it in /usr/lib.
    However not all build scripts look for these hard enough, so you may need
    to call ENV.libxml2 in your formula's install function.
    EOS
  when 'wxwidgets' then <<-EOS.undent
    An old version of wxWidgets can be found in /usr/X11/lib. However, Homebrew
    does provide a newer version:

        brew install wxmac
    EOS
  when 'tex', 'tex-live', 'texlive' then <<-EOS.undent
    Installing TeX from source is weird and gross, requires a lot of patches,
    and only builds 32-bit (and thus can't use Homebrew deps on Snow Leopard.)

    We recommend using a MacTeX distribution: http://www.tug.org/mactex/
    EOS
  when 'pip' then <<-EOS.undent
    pip is installed by `brew install python`
    EOS
  when 'macruby' then <<-EOS.undent
    MacRuby works better when you install their package:
      http://www.macruby.org/
    EOS
  when /(lib)?lzma/
    "lzma is now part of the xz formula."
  when 'xcode' then <<-EOS.undent
    Xcode can be installed via the App Store (on Lion or newer), or from:
      http://connect.apple.com/
    EOS
  end
end