Add cxxstdlib_check method to request changing C++ stdlib checking.

* In certain cases, a C++ software may result in linking to a different
  and incompatible C++ standard library than its dependencies and still
  works fine because it is by design. Examples include GCC, which will
  bootstrap itself and self-host after finish.

* Add a cxxstdlib_check method to formula to request changing the C++
  standard library checking. Currently using "cxxstdlib_check :skip"
  will let a formula skip such checking. This should only be used on
  rare occasions and be very careful.

Closes Homebrew/homebrew#23687.

1 files changed, 12 insertions, 0 deletions

diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index fd1884e4f..a760e7fc2 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -25,6 +25,10 @@ class Formula
 
   attr_accessor :local_bottle_path
 
+  # Flag for marking whether this formula needs C++ standard library
+  # compatibility check
+  attr_reader :cxxstdlib
+
   # Homebrew determines the name
   def initialize name='__UNKNOWN__', path=nil
     @name = name
@@ -52,6 +56,8 @@ class Formula
     @build = determine_build_options
 
     @pin = FormulaPin.new(self)
+
+    @cxxstdlib ||= Set.new
   end
 
   def set_spec(name)
@@ -643,6 +649,12 @@ class Formula
     end
   end
 
+  # Explicitly request changing C++ standard library compatibility check
+  # settings. Use with caution!
+  def cxxstdlib_check check_type
+    @cxxstdlib << check_type
+  end
+
   def self.method_added method
     case method
     when :brew