Support env :std, :userpaths

Closes Homebrew/homebrew#14654.

Library/Homebrew/build.rb

@@ -53,32 +53,17 @@ rescue Exception => e
 end
 
 def post_superenv_hacks f
-  # TODO replace with Formula DSL
-  # Python etc. build but then pip can't build stuff.
-  # Scons resets ENV and then can't find superenv's build-tools.
-  # In some cases we should only apply in the case of an option I suggest the
-  # following:
-  #
-  # option 'with-passenger' do
-  #   env :userpaths  # for superenv
-  # end
-  # option 'without-foo' do
-  #  env :std, :x11
-  # end
-  #
-  # NOTE I think all ENV stuff should be specified with a DSL like this now.
-  case f.name.to_sym
-  when :lilypond, :nginx, :auctex
+  # Only allow Homebrew-approved directories into the PATH, unless
+  # a formula opts-in to allowing the user's path.
+  if f.env.userpaths?
     paths = ORIGINAL_PATHS.map{|pn| pn.realpath.to_s rescue nil } - %w{/usr/X11/bin /opt/X11/bin}
     ENV['PATH'] = "#{ENV['PATH']}:#{paths.join(':')}"
   end
 end
 
 def pre_superenv_hacks f
-  # fontforge needs 10.7 SDK, wine 32 bit, graphviz has mysteriously missing symbols
-  # and ruby/python/ghc etc. create gem/pip that then won't work
-  stdenvs = %w{fontforge python python3 ruby ruby-enterprise-edition jruby wine graphviz ghc}
-  ARGV.unshift '--env=std' if (stdenvs.include?(f.name) or
+  # Allow a formula to opt-in to the std environment.
+  ARGV.unshift '--env=std' if (f.env.std? or
     f.recursive_deps.detect{|d| d.name == 'scons' }) and
     not ARGV.include? '--env=super'
 end

Library/Homebrew/build_environment.rb

@@ -0,0 +1,15 @@
+require 'set'
+
+class BuildEnvironment
+  def initialize settings
+    @settings = Set.new(settings)
+  end
+
+  def std?
+    @settings.include? :std
+  end
+
+  def userpaths?
+    @settings.include? :userpaths
+  end
+end

Library/Homebrew/formula.rb

@@ -6,6 +6,7 @@ require 'bottles'
 require 'extend/fileutils'
 require 'patches'
 require 'compilers'
+require 'build_environment'
 
 
 class Formula
@@ -436,6 +437,10 @@ class Formula
   def deps;         self.class.dependencies.deps;         end
   def requirements; self.class.dependencies.requirements; end
 
+  def env
+    @env ||= BuildEnvironment.new(self.class.environments)
+  end
+
   def conflicts
     requirements.select { |r| r.is_a? ConflictRequirement }
   end
@@ -646,6 +651,14 @@ private
       @stable.mirror(val)
     end
 
+    def environments
+      @environments ||= []
+    end
+
+    def env *settings
+      environments.concat [settings].flatten
+    end
+
     def dependencies
       @dependencies ||= DependencyCollector.new
     end