ENV: mark gcc-6 as supporting C++11 (#349)

Add SharedEnvExtension#gcc_with_cxx11_support? to centralise the
logic for checking whether a compiler is known to support C++11.

Update logic to accept GCC 4.8 and above (including 6). Thereby also
address oversight in #163 where support for GCC 6 was added without
updating the C++11 compiler whitelist.

Add tests for Superenv#cxx11.

Closes #346.

1 files changed, 29 insertions, 0 deletions

diff --git a/Library/Homebrew/test/test_ENV.rb b/Library/Homebrew/test/test_ENV.rb
index 74d1cff79..665e344e6 100644
--- a/Library/Homebrew/test/test_ENV.rb
+++ b/Library/Homebrew/test/test_ENV.rb
@@ -141,4 +141,33 @@ class SuperenvTests < Homebrew::TestCase
     assert_equal [], @env.deps
     assert_equal [], @env.keg_only_deps
   end
+
+  def test_unsupported_cxx11
+    %w[gcc gcc-4.7].each do |compiler|
+      @env["HOMEBREW_CC"] = compiler
+      assert_raises do
+        @env.cxx11
+      end
+      refute_match "x", @env["HOMEBREW_CCCFG"]
+    end
+  end
+
+  def test_supported_cxx11_gcc_5
+    @env["HOMEBREW_CC"] = "gcc-5"
+    @env.cxx11
+    assert_match "x", @env["HOMEBREW_CCCFG"]
+  end
+
+  def test_supported_cxx11_gcc_6
+    @env["HOMEBREW_CC"] = "gcc-6"
+    @env.cxx11
+    assert_match "x", @env["HOMEBREW_CCCFG"]
+  end
+
+  def test_supported_cxx11_clang
+    @env["HOMEBREW_CC"] = "clang"
+    @env.cxx11
+    assert_match "x", @env["HOMEBREW_CCCFG"]
+    assert_match "g", @env["HOMEBREW_CCCFG"]
+  end
 end