Use xcrun; Ensure clang is the default compiler with Xcode 4.3

Using xcrun as a proxy to execute the compiler tools is per its design. This means you can't treat ENV['CC'] as a path anymore, but I think I found the cases this was being expected and corrected them. It was not proper anyway to assume the variable was a path, it can be anything. Like a proxy. Like xcrun.

Also more thoroughly clear ENV.

Library/Homebrew/cmd/--env.rb

@@ -18,9 +18,11 @@ module Homebrew extend self
       value = env[k]
       if value
         results = value
-        if File.exists? value and File.symlink? value
-          target = Pathname.new(value)
-          results += " => #{target.realpath}"
+        if value =~ %r{^/usr/bin/xcrun (.*)}
+          path = `/usr/bin/xcrun -find #{$1}`
+          results += " => #{path}"
+        elsif File.exists? value and File.symlink? value
+          results += " => #{Pathname.new(value).realpath}"
         end
         puts "#{k}: #{results}"
       end

Library/Homebrew/extend/ENV.rb

@@ -5,10 +5,9 @@ module HomebrewEnvExtension
   def setup_build_environment
     # Clear CDPATH to avoid make issues that depend on changing directories
     delete('CDPATH')
-    delete('CPPFLAGS')
-    delete('LDFLAGS')
     delete('GREP_OPTIONS') # can break CMake (lol)
     delete('CLICOLOR_FORCE') # autotools doesn't like this
+    remove_cc_etc
 
     self['MAKEFLAGS'] = "-j#{self.make_jobs}"
 
@@ -27,10 +26,9 @@ module HomebrewEnvExtension
     self.send self.compiler
 
     # we must have a working compiler!
-    unless File.exist? ENV['CC'] and File.exist? ENV['CXX']
+    unless ENV['CC']
       @compiler = MacOS.default_compiler
       self.send @compiler
-
       ENV['CC']  = '/usr/bin/cc'
       ENV['CXX'] = '/usr/bin/c++'
     end
@@ -79,6 +77,7 @@ module HomebrewEnvExtension
   end
 
   def gcc_4_0_1
+    # we don't use xcrun because gcc 4.0 has not been provided since Xcode 4
     self['CC'] =  "#{MacOS.dev_tools_path}/gcc-4.0"
     self['CXX'] = "#{MacOS.dev_tools_path}/g++-4.0"
     replace_in_cflags '-O4', '-O3'
@@ -87,34 +86,66 @@ module HomebrewEnvExtension
   end
   alias_method :gcc_4_0, :gcc_4_0_1
 
+  def xcrun tool
+    if File.executable? "/usr/bin/#{tool}"
+      "/usr/bin/#{tool}"
+    elsif system "/usr/bin/xcrun -find #{tool} 2>1 1>/dev/null"
+      # xcrun was provided first with Xcode 4.3 and allows us to proxy
+      # tool usage thus avoiding various bugs
+      "/usr/bin/xcrun #{tool}"
+    else
+      # otherwise lets try and figure it out ourselves
+      fn = "#{MacOS.dev_tools_path}/#{tool}"
+      if File.file? fn
+        fn
+      else
+        nil
+      end
+    end
+  end
+
+  # if your formula doesn't like CC having spaces use this
+  def expand_xcrun
+    ENV['CC'] =~ %r{/usr/bin/xcrun (.*)}
+    ENV['CC'] = `/usr/bin/xcrun -find #{$1}`.chomp if $1
+    ENV['CXX'] =~ %r{/usr/bin/xcrun (.*)}
+    ENV['CXX'] = `/usr/bin/xcrun -find #{$1}`.chomp if $1
+  end
+
   def gcc args = {}
     # Apple stopped shipping gcc-4.2 with Xcode 4.2
     # However they still provide a gcc symlink to llvm
     # But we don't want LLVM of course.
 
-    gcc_path = Pathname.new "#{MacOS.dev_tools_path}/gcc-4.2"
-    gxx_path = Pathname.new "#{MacOS.dev_tools_path}/g++-4.2"
-    self['CC']  = gcc_path.exist? ? gcc_path : HOMEBREW_PREFIX+'bin/gcc-4.2'
-    self['CXX'] = gxx_path.exist? ? gxx_path : HOMEBREW_PREFIX+'bin/g++-4.2'
+    ENV['CC'] = xcrun "gcc-4.2"
+    ENV['CXX'] = xcrun "g++-4.2"
+
+    unless ENV['CC']
+      ENV['CC'] = "#{HOMEBREW_PREFIX}/bin/gcc-4.2"
+      ENV['CXX'] = "#{HOMEBREW_PREFIX}/bin/g++-4.2"
+      raise "GCC could not be found" if not File.exist? ENV['CC']
+    end
+
+    if not ENV['CC'] =~ %r{^/usr/bin/xcrun}
+      raise "GCC could not be found" if Pathname.new(ENV['CC']).realpath.to_s =~ /llvm/
+    end
+
     replace_in_cflags '-O4', '-O3'
     set_cpu_cflags 'core2 -msse4', :penryn => 'core2 -msse4.1', :core2 => 'core2', :core => 'prescott', :bottle => 'generic'
     @compiler = :gcc
-
-    raise "GCC could not be found" if not File.exist? ENV['CC'] \
-                                   or (Pathname.new(ENV['CC']).realpath.to_s =~ /llvm/)
   end
   alias_method :gcc_4_2, :gcc
 
   def llvm
-    self['CC']  = "#{MacOS.dev_tools_path}/llvm-gcc"
-    self['CXX'] = "#{MacOS.dev_tools_path}/llvm-g++"
+    self['CC']  = xcrun "llvm-gcc"
+    self['CXX'] = xcrun "llvm-g++"
     set_cpu_cflags 'core2 -msse4', :penryn => 'core2 -msse4.1', :core2 => 'core2', :core => 'prescott'
     @compiler = :llvm
   end
 
   def clang args = {}
-    self['CC']  = "#{MacOS.dev_tools_path}/clang"
-    self['CXX'] = "#{MacOS.dev_tools_path}/clang++"
+    self['CC']  = xcrun "clang"
+    self['CXX'] = xcrun "clang++"
     replace_in_cflags(/-Xarch_i386 (-march=\S*)/, '\1')
     # Clang mistakenly enables AES-NI on plain Nehalem
     set_cpu_cflags 'native', :nehalem => 'native -Xclang -target-feature -Xclang -aes'

Library/Homebrew/utils.rb

@@ -267,11 +267,9 @@ module MacOS extend self
   end
 
   def default_cc
-    cc = Pathname.new("#{dev_tools_path}/cc")
-    # Xcode 4.3.0 has no /Applications/Xcode/Contents/Developer/usr/bin/cc
-    # Xcode 4.3.0 has no GCC
-    cc = Pathname.new("#{dev_tools_path}/llvm-gcc") unless cc.file?
-    cc.realpath.basename.to_s
+    cc = `/usr/bin/xcrun -find cc 2> /dev/null`.chomp
+    cc = "#{dev_tools_path}/cc" if cc.empty?
+    Pathname.new(cc).realpath.basename.to_s
   end
 
   def default_compiler
@@ -281,7 +279,9 @@ module MacOS extend self
       when "clang" then :clang
       else
         # guess :(
-        if xcode_version >= "4.2"
+        if xcode_version >= "4.3"
+          :clang
+        elsif xcode_version >= "4.2"
           :llvm
         else
           :gcc