Move CompilerSelector logic into build env setup

This moves the CompilerSelector fails_with logic into the build
environment setup, making the compiler selection available before
performing actions that depends on knowing what the compiler is, e.g.
setting up PATH.

ENV.setup_build_environment now optionally takes a Formula argument
to provide the information necessary to do the fails_with, and the new
ENV.validate_cc! extracts the fails_with logic from Build.install.

Library/Homebrew/build.rb

@@ -120,12 +120,12 @@ class Build
       ENV.keg_only_deps = keg_only_deps.map(&:to_s)
       ENV.deps = deps.map { |d| d.to_formula.to_s }
       ENV.x11 = reqs.any? { |rq| rq.kind_of?(X11Dependency) }
-      ENV.setup_build_environment
+      ENV.setup_build_environment(f)
       post_superenv_hacks
       reqs.each(&:modify_build_environment)
       deps.each(&:modify_build_environment)
     else
-      ENV.setup_build_environment
+      ENV.setup_build_environment(f)
       reqs.each(&:modify_build_environment)
       deps.each(&:modify_build_environment)
 
@@ -141,14 +141,6 @@ class Build
       end
     end
 
-    if f.fails_with? ENV.compiler
-      begin
-        ENV.send CompilerSelector.new(f).compiler
-      rescue CompilerSelectionError => e
-        raise e.message
-      end
-    end
-
     # We only support libstdc++ right now
     stdlib_in_use = CxxStdlib.new(:libstdcxx, ENV.compiler)
 

Library/Homebrew/extend/ENV/shared.rb

@@ -111,6 +111,19 @@ module SharedEnvExtension
     end
   end
 
+  # If the given compiler isn't compatible, will try to select
+  # an alternate compiler, altering the value of environment variables.
+  # If no valid compiler is found, raises an exception.
+  def validate_cc!(formula)
+    if formula.fails_with? ENV.compiler
+      begin
+        send CompilerSelector.new(formula).compiler
+      rescue CompilerSelectionError => e
+        raise e.message
+      end
+    end
+  end
+
   # Snow Leopard defines an NCURSES value the opposite of most distros
   # See: http://bugs.python.org/issue6848
   # Currently only used by aalib in core
@@ -162,7 +175,7 @@ module SharedEnvExtension
 
     begin
       gcc_name = 'gcc' + gcc.delete('.')
-      gcc = Formula.factory(gcc_name)
+      gcc = Formulary.factory(gcc_name)
       if !gcc.installed?
         raise <<-EOS.undent
         The requested Homebrew GCC, #{gcc_name}, was not installed.
@@ -171,8 +184,6 @@ module SharedEnvExtension
           brew install #{gcc_name}
         EOS
       end
-
-      ENV.append('PATH', gcc.opt_prefix/'bin', ':')
     rescue FormulaUnavailableError
       raise <<-EOS.undent
       Homebrew GCC requested, but formula #{gcc_name} not found!

Library/Homebrew/extend/ENV/std.rb

@@ -14,7 +14,7 @@ module Stdenv
     end
   end
 
-  def setup_build_environment
+  def setup_build_environment(formula=nil)
     # Clear CDPATH to avoid make issues that depend on changing directories
     delete('CDPATH')
     delete('GREP_OPTIONS') # can break CMake (lol)
@@ -68,8 +68,13 @@ module Stdenv
       self.cxx = MacOS.locate("c++")
     end
 
+    validate_cc!(formula) unless formula.nil?
+
     if cc =~ GNU_GCC_REGEXP
       warn_about_non_apple_gcc($1)
+      gcc_name = 'gcc' + $1.delete('.')
+      gcc = Formulary.factory(gcc_name)
+      self.append_path('PATH', gcc.opt_prefix/'bin')
     end
 
     # Add lib and include etc. from the current macosxsdk to compiler flags:

Library/Homebrew/extend/ENV/super.rb

@@ -54,16 +54,18 @@ module Superenv
     delete('CLICOLOR_FORCE') # autotools doesn't like this
   end
 
-  def setup_build_environment
+  def setup_build_environment(formula=nil)
     reset
+
     self.cc  = 'cc'
     self.cxx = 'c++'
+    self['HOMEBREW_CC'] = determine_cc
+    validate_cc!(formula) unless formula.nil?
     self['DEVELOPER_DIR'] = determine_developer_dir
     self['MAKEFLAGS'] ||= "-j#{determine_make_jobs}"
     self['PATH'] = determine_path
     self['PKG_CONFIG_PATH'] = determine_pkg_config_path
     self['PKG_CONFIG_LIBDIR'] = determine_pkg_config_libdir
-    self['HOMEBREW_CC'] = determine_cc
     self['HOMEBREW_CCCFG'] = determine_cccfg
     self['HOMEBREW_BREW_FILE'] = HOMEBREW_BREW_FILE
     self['HOMEBREW_SDKROOT'] = "#{MacOS.sdk_path}" if MacOS::Xcode.without_clt?
@@ -99,20 +101,7 @@ module Superenv
     # s - apply fix for sed's Unicode support
     # a - apply fix for apr-1-config path
 
-    # Homebrew's apple-gcc42 will be outside the PATH in superenv,
+    warn_about_non_apple_gcc($1) if ENV['HOMEBREW_CC'] =~ GNU_GCC_REGEXP
-    # so xcrun may not be able to find it
-    if self['HOMEBREW_CC'] == 'gcc-4.2'
-      apple_gcc42 = begin
-        Formulary.factory('apple-gcc42')
-      rescue Exception # in --debug, catch bare exceptions too
-        nil
-      end
-      append_path('PATH', apple_gcc42.opt_prefix/'bin') if apple_gcc42
-    end
-
-    if ENV['HOMEBREW_CC'] =~ GNU_GCC_REGEXP
-      warn_about_non_apple_gcc($1)
-    end
   end
 
   def universal_binary
@@ -141,6 +130,24 @@ module Superenv
     paths += deps.map{|dep| "#{HOMEBREW_PREFIX}/opt/#{dep}/bin" }
     paths << MacOS::X11.bin if x11?
     paths += %w{/usr/bin /bin /usr/sbin /sbin}
+
+    # Homebrew's apple-gcc42 will be outside the PATH in superenv,
+    # so xcrun may not be able to find it
+    if self['HOMEBREW_CC'] == 'gcc-4.2'
+      apple_gcc42 = begin
+        Formulary.factory('apple-gcc42')
+      rescue Exception # in --debug, catch bare exceptions too
+        nil
+      end
+      paths << apple_gcc42.opt_prefix/'bin' if apple_gcc42
+    end
+
+    if self['HOMEBREW_CC'] =~ GNU_GCC_REGEXP
+      gcc_name = 'gcc' + $1.delete('.')
+      gcc = Formulary.factory(gcc_name)
+      paths << gcc.opt_prefix/'bin'
+    end
+
     paths.to_path_s
   end