C++11 support.

* Add options and ENV method to specify building in C++11 mode.
  - Set C++ compiler flags to enable C++11 mode.
  - To add options to support C++11 mode, a formula can now use

      option :cxx11

    to provide "--c++11" option, and detect and enable C++11 support in
    install method using

      ENV.cxx11 if build.cxx11?

Closes Homebrew/homebrew#22453.

2 files changed, 24 insertions, 0 deletions

diff --git a/Library/Homebrew/extend/ENV/std.rb b/Library/Homebrew/extend/ENV/std.rb
index bca0df041..0d5613256 100644
--- a/Library/Homebrew/extend/ENV/std.rb
+++ b/Library/Homebrew/extend/ENV/std.rb
@@ -322,6 +322,17 @@ module Stdenv
     end
   end
 
+  def cxx11
+    if compiler == :clang
+      append 'CXX', '-std=c++11'
+      append 'CXX', '-stdlib=libc++'
+    elsif compiler =~ /gcc-4\.(8|9)/
+      append 'CXX', '-std=c++11'
+    else
+      raise "The selected compiler doesn't support C++11: #{compiler}"
+    end
+  end
+
   def replace_in_cflags before, after
     CC_FLAG_VARS.each do |key|
       self[key] = self[key].sub(before, after) if has_key?(key)
diff --git a/Library/Homebrew/extend/ENV/super.rb b/Library/Homebrew/extend/ENV/super.rb
index e3f9ed923..2be8a62d4 100644
--- a/Library/Homebrew/extend/ENV/super.rb
+++ b/Library/Homebrew/extend/ENV/super.rb
@@ -97,6 +97,8 @@ module Superenv
     # A - Installing from a bottle on PPC with Altivec
     # O - Enables argument refurbishing. Only active under the
     #     make/bsdmake wrappers currently.
+    # x - Enable C++11 mode.
+    # g - Enable "-stdlib=libc++" for clang.
     #
     # On 10.8 and newer, these flags will also be present:
     # s - apply fix for sed's Unicode support
@@ -110,6 +112,17 @@ module Superenv
     append 'HOMEBREW_CCCFG', "u", ''
   end
 
+  def cxx11
+    if self['HOMEBREW_CC'] == 'clang'
+      append 'HOMEBREW_CCCFG', "x", ''
+      append 'HOMEBREW_CCCFG', "g", ''
+    elsif self['HOMEBREW_CC'] =~ /gcc-4\.(8|9)/
+      append 'HOMEBREW_CCCFG', "x", ''
+    else
+      raise "The selected compiler doesn't support C++11: #{self['HOMEBREW_CC']}"
+    end
+  end
+
   # m32 on superenv does not add any CC flags. It prevents "-m32" from being erased.
   def m32
     append 'HOMEBREW_CCCFG', "3", ''