Tab: track C++ stdlib in use

There are subtle incompatibilities between Apple's libstdc++ and the
libstdc++ used by the various GNU GCC formulae. In addition, we'll
likely also be supporting libc++ in the future, and that's also
incompatible with the other stdlibs.

Tracking it in the tab lets us make sure that dependencies are all
built against the same stdlib to avoid subtle breakage.

1 files changed, 44 insertions, 0 deletions

diff --git a/Library/Homebrew/cxxstdlib.rb b/Library/Homebrew/cxxstdlib.rb
new file mode 100644
index 000000000..4e3bed22e
--- /dev/null
+++ b/Library/Homebrew/cxxstdlib.rb
@@ -0,0 +1,44 @@
+class CxxStdlib
+  attr_accessor :type, :compiler
+
+  def initialize(type, compiler)
+    if ![:libstdcxx, :libcxx].include? type
+      raise ArgumentError, "Invalid C++ stdlib type: #{type}"
+    end
+
+    @type     = type.to_sym
+    @compiler = compiler.to_sym
+  end
+
+  def apple_compiler?
+    not compiler.to_s =~ SharedEnvExtension::GNU_GCC_REGEXP
+  end
+
+  def compatible_with?(other)
+    # libstdc++ and libc++ aren't ever intercompatible
+    return false unless type == other.type
+
+    # libstdc++ is compatible across Apple compilers, but
+    # not between Apple and GNU compilers, or between GNU compiler versions
+    return false if apple_compiler? && !other.apple_compiler?
+    if compiler.to_s =~ SharedEnvExtension::GNU_GCC_REGEXP
+      return false unless other.compiler.to_s =~ SharedEnvExtension::GNU_GCC_REGEXP
+      return false unless compiler.to_s[4..6] == other.compiler.to_s[4..6]
+    end
+
+    true
+  end
+
+  def check_dependencies(formula, deps)
+    deps.each do |dep|
+      dep_stdlib = Tab.for_formula(dep.to_formula).cxxstdlib
+      if !compatible_with? dep_stdlib
+        raise IncompatibleCxxStdlibs.new(formula, dep, dep_stdlib, self)
+      end
+    end
+  end
+
+  def type_string
+    type.to_s.gsub(/cxx$/, 'c++')
+  end
+end