Decouple CompilerSelector from ENV

Library/Homebrew/build.rb

@@ -114,7 +114,7 @@ def install f
     end
   end
 
-  CompilerSelector.new(f).select_compiler if f.fails_with? ENV.compiler
+  ENV.send(CompilerSelector.new(f).compiler) if f.fails_with? ENV.compiler
 
   f.brew do
     if ARGV.flag? '--git'

Library/Homebrew/compilers.rb

@@ -56,11 +56,11 @@ class CompilerSelector
     end
   end
 
-  def select_compiler
+  def compiler
     begin
       cc = @compilers.pop
     end while @f.fails_with?(cc)
-    ENV.send(cc.name) unless cc.nil?
+    cc.nil? ? @old_compiler : cc.name
   end
 
   private

Library/Homebrew/test/test_compilers.rb

@@ -2,14 +2,6 @@ require 'testing_env'
 require 'test/testball'
 
 class CompilerTests < Test::Unit::TestCase
-  def setup
-    %w{HOMEBREW_USE_CLANG HOMEBREW_USE_LLVM HOMEBREW_USE_GCC}.each { |v| ENV.delete(v) }
-  end
-
-  def teardown
-    ENV.send MacOS.default_compiler
-  end
-
   def test_llvm_failure
     f = TestLLVMFailure.new
     cs = CompilerSelector.new(f)
@@ -17,13 +9,10 @@ class CompilerTests < Test::Unit::TestCase
     assert !(f.fails_with? :clang)
     assert f.fails_with? :llvm
     assert !(f.fails_with? :gcc)
-
-    cs.select_compiler
-
     assert_equal case MacOS.clang_build_version
       when 0..210 then :gcc
       else :clang
-      end, ENV.compiler
+      end, cs.compiler
   end
 
   def test_all_compiler_failures
@@ -33,10 +22,7 @@ class CompilerTests < Test::Unit::TestCase
     assert f.fails_with? :clang
     assert f.fails_with? :llvm
     assert f.fails_with? :gcc
-
+    assert_equal MacOS.default_compiler, cs.compiler
-    cs.select_compiler
-
-    assert_equal MacOS.default_compiler, ENV.compiler
   end
 
   def test_no_compiler_failures
@@ -49,10 +35,7 @@ class CompilerTests < Test::Unit::TestCase
       when nil then f.fails_with? :gcc
       else !(f.fails_with? :gcc)
       end
-
+    assert_equal MacOS.default_compiler, cs.compiler
-    cs.select_compiler
-
-    assert_equal MacOS.default_compiler, ENV.compiler
   end
 
   def test_mixed_compiler_failures
@@ -62,10 +45,7 @@ class CompilerTests < Test::Unit::TestCase
     assert f.fails_with? :clang
     assert !(f.fails_with? :llvm)
     assert f.fails_with? :gcc
-
+    assert_equal :llvm, cs.compiler
-    cs.select_compiler
-
-    assert_equal :llvm, ENV.compiler
   end
 
   def test_more_mixed_compiler_failures
@@ -75,10 +55,7 @@ class CompilerTests < Test::Unit::TestCase
     assert !(f.fails_with? :clang)
     assert f.fails_with? :llvm
     assert f.fails_with? :gcc
-
+    assert_equal :clang, cs.compiler
-    cs.select_compiler
-
-    assert_equal :clang, ENV.compiler
   end
 
   def test_even_more_mixed_compiler_failures
@@ -91,13 +68,10 @@ class CompilerTests < Test::Unit::TestCase
       when nil then f.fails_with? :gcc
       else !(f.fails_with? :gcc)
       end
-
-    cs.select_compiler
-
     assert_equal case MacOS.gcc_42_build_version
       when nil then :llvm
       else :gcc
-      end, ENV.compiler
+      end, cs.compiler
   end
 
   def test_block_with_no_build_compiler_failures
@@ -107,9 +81,6 @@ class CompilerTests < Test::Unit::TestCase
     assert f.fails_with? :clang
     assert !(f.fails_with? :llvm)
     assert !(f.fails_with? :gcc)
-
+    assert_not_equal :clang, cs.compiler
-    cs.select_compiler
-
-    assert_not_equal :clang, ENV.compiler
   end
 end