Add ENV.cxx14 and option :cxx14

Library/Homebrew/build_options.rb

@@ -83,6 +83,11 @@ def cxx11?
     include?("c++11") && option_defined?("c++11")
   end
 
+  # True if a {Formula} is being built in C++14 mode.
+  def cxx14?
+    include?("c++14") && option_defined?("c++14")
+  end
+
   # @private
   def used_options
     @options & @args

Library/Homebrew/extend/ENV/shared.rb

@@ -337,6 +337,11 @@ def gcc_with_cxx11_support?(cc)
     version = cc[/^gcc-(\d+(?:\.\d+)?)$/, 1]
     version && Version.create(version) >= Version.create("4.8")
   end
+
+  def gcc_with_cxx14_support?(cc)
+    version = cc[/^gcc-(\d+(?:\.\d+)?)$/, 1]
+    version && Version.create(version) >= Version.create("5")
+  end
 end
 
 require "extend/os/extend/ENV/shared"

Library/Homebrew/extend/ENV/std.rb

@@ -175,6 +175,17 @@ def cxx11
     end
   end
 
+  def cxx14
+    if compiler == :clang
+      append "CXX", "-std=c++14"
+      append "CXX", "-stdlib=libc++"
+    elsif gcc_with_cxx14_support?(compiler)
+      append "CXX", "-std=c++14"
+    else
+      raise "The selected compiler doesn't support C++14: #{compiler}"
+    end
+  end
+
   def libcxx
     append "CXX", "-stdlib=libc++" if compiler == :clang
   end

Library/Homebrew/extend/ENV/super.rb

@@ -71,6 +71,7 @@ def setup_build_environment(formula = nil)
     # O - Enables argument refurbishing. Only active under the
     #     make/bsdmake wrappers currently.
     # x - Enable C++11 mode.
+    # y - Enable C++14 mode.
     # g - Enable "-stdlib=libc++" for clang.
     # h - Enable "-stdlib=libstdc++" for clang.
     # K - Don't strip -arch <arch>, -m32, or -m64
@@ -305,6 +306,17 @@ def cxx11
     end
   end
 
+  def cxx14
+    if homebrew_cc == "clang"
+      append "HOMEBREW_CCCFG", "y", ""
+      append "HOMEBREW_CCCFG", "g", ""
+    elsif gcc_with_cxx14_support?(homebrew_cc)
+      append "HOMEBREW_CCCFG", "y", ""
+    else
+      raise "The selected compiler doesn't support C++14: #{homebrew_cc}"
+    end
+  end
+
   def libcxx
     append "HOMEBREW_CCCFG", "g", "" if compiler == :clang
   end

Library/Homebrew/rubocops/options_cop.rb

@@ -30,6 +30,7 @@ def audit_formula(_node, _class_node, _parent_class_node, body_node)
 
             if option !~ /with(out)?-/ &&
                option != "cxx11" &&
+               option != "cxx14" &&
                option != "universal"
               problem "Options should begin with with/without."\
                       " Migrate '--#{option}' with `deprecated_option`."

Library/Homebrew/shims/super/cc

@@ -245,6 +245,7 @@ class Cmd
   def cxxflags
     args = cflags
     args << "-std=c++11" if cxx11?
+    args << "-std=c++14" if cxx14?
     args << "-stdlib=libc++" if libcxx?
     args << "-stdlib=libstdc++" if libstdcxx?
     args
@@ -298,6 +299,10 @@ class Cmd
     config.include?("x")
   end
 
+  def cxx14?
+    config.include?("y")
+  end
+
   def libcxx?
     config.include?("g")
   end

Library/Homebrew/software_spec.rb

@@ -15,6 +15,7 @@ class SoftwareSpec
   PREDEFINED_OPTIONS = {
     universal: Option.new("universal", "Build a universal binary"),
     cxx11:     Option.new("c++11",     "Build using C++11 mode"),
+    cxx14:     Option.new("c++14",     "Build using C++14 mode"),
   }.freeze
 
   attr_reader :name, :full_name, :owner

Library/Homebrew/tab.rb

@@ -228,6 +228,10 @@ def cxx11?
     include?("c++11")
   end
 
+  def cxx14?
+    include?("c++14")
+  end
+
   def head?
     spec == :head
   end

Library/Homebrew/test/ENV_spec.rb

@@ -186,4 +186,36 @@
       expect(subject["HOMEBREW_CCCFG"]).to include("g")
     end
   end
+
+  describe "#cxx14" do
+    it "raises an error when the compiler isn't supported" do
+      %w[gcc gcc-4.7 gcc-4.8 gcc-4.9].each do |compiler|
+        subject["HOMEBREW_CC"] = compiler
+
+        expect { subject.cxx14 }
+          .to raise_error(/The selected compiler doesn't support C\+\+14:/)
+
+        expect(subject["HOMEBREW_CCCFG"]).to be nil
+      end
+    end
+
+    it "supports gcc-5" do
+      subject["HOMEBREW_CC"] = "gcc-5"
+      subject.cxx14
+      expect(subject["HOMEBREW_CCCFG"]).to include("y")
+    end
+
+    example "supports gcc-6" do
+      subject["HOMEBREW_CC"] = "gcc-6"
+      subject.cxx14
+      expect(subject["HOMEBREW_CCCFG"]).to include("y")
+    end
+
+    it "supports clang" do
+      subject["HOMEBREW_CC"] = "clang"
+      subject.cxx14
+      expect(subject["HOMEBREW_CCCFG"]).to include("y")
+      expect(subject["HOMEBREW_CCCFG"]).to include("g")
+    end
+  end
 end

Library/Homebrew/test/software_spec_spec.rb

@@ -79,6 +79,12 @@
       expect(subject).not_to have_defined_option("cxx11")
     end
 
+    it "special cases the cxx14 option" do
+      subject.option(:cxx14)
+      expect(subject).to have_defined_option("c++14")
+      expect(subject).not_to have_defined_option("cxx14")
+    end
+
     it "supports options with descriptions" do
       subject.option("bar", "description")
       expect(subject.options.first.description).to eq("description")