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.

Library/Homebrew/build.rb

@@ -170,7 +170,8 @@ class Build
 
         begin
           f.install
-          Tab.create(f, Options.coerce(ARGV.options_only)).write
+          Tab.create(f, ENV.compiler,
+            Options.coerce(ARGV.options_only)).write
         rescue Exception => e
           if ARGV.debug?
             debrew e, f

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

Library/Homebrew/tab.rb

@@ -1,3 +1,4 @@
+require 'cxxstdlib'
 require 'ostruct'
 require 'options'
 require 'utils/json'
@@ -9,7 +10,7 @@ require 'utils/json'
 class Tab < OpenStruct
   FILENAME = 'INSTALL_RECEIPT.json'
 
-  def self.create f, args
+  def self.create f, stdlib, compiler, args
     f.build.args = args
 
     sha = HOMEBREW_REPOSITORY.cd do
@@ -23,7 +24,9 @@ class Tab < OpenStruct
             :poured_from_bottle => false,
             :tapped_from => f.tap,
             :time => Time.now.to_i, # to_s would be better but Ruby has no from_s function :P
-            :HEAD => sha
+            :HEAD => sha,
+            :compiler => compiler,
+            :stdlib => stdlib
   end
 
   def self.from_file path
@@ -59,7 +62,9 @@ class Tab < OpenStruct
             :poured_from_bottle => false,
             :tapped_from => "",
             :time => nil,
-            :HEAD => nil
+            :HEAD => nil,
+            :stdlib => :libstdcxx,
+            :compiler => :clang
   end
 
   def with? name
@@ -92,6 +97,13 @@ class Tab < OpenStruct
     used_options + unused_options
   end
 
+  def cxxstdlib
+    # Older tabs won't have these values, so provide sensible defaults
+    lib = stdlib || :libstdcxx
+    cc = compiler || MacOS.default_compiler
+    CxxStdlib.new(lib.to_sym, cc.to_sym)
+  end
+
   def to_json
     Utils::JSON.dump({
       :used_options => used_options.map(&:to_s),
@@ -100,7 +112,9 @@ class Tab < OpenStruct
       :poured_from_bottle => poured_from_bottle,
       :tapped_from => tapped_from,
       :time => time,
-      :HEAD => send("HEAD")})
+      :HEAD => send("HEAD"),
+      :stdlib => (stdlib.to_s if stdlib),
+      :compiler => (compiler.to_s if compiler)})
   end
 
   def write

Library/Homebrew/test/test_stdlib.rb

@@ -0,0 +1,62 @@
+require 'testing_env'
+require 'test/testball'
+require 'formula'
+require 'cxxstdlib'
+require 'tab'
+
+class CxxStdlibTests < Test::Unit::TestCase
+  def setup
+    @clang = CxxStdlib.new(:libstdcxx, :clang)
+    @gcc   = CxxStdlib.new(:libstdcxx, :gcc)
+    @llvm  = CxxStdlib.new(:libstdcxx, :llvm)
+    @gcc4  = CxxStdlib.new(:libstdcxx, :gcc_4_0)
+    @gcc48 = CxxStdlib.new(:libstdcxx, 'gcc-4.8')
+    @gcc49 = CxxStdlib.new(:libstdcxx, 'gcc-4.9')
+    @lcxx  = CxxStdlib.new(:libcxx, :clang)
+  end
+
+  def test_apple_libstdcxx_intercompatibility
+    assert @clang.compatible_with?(@gcc)
+    assert @clang.compatible_with?(@llvm)
+    assert @clang.compatible_with?(@gcc4)
+  end
+
+  def test_compatibility_same_compilers_and_type
+    assert @gcc48.compatible_with?(@gcc48)
+    assert @clang.compatible_with?(@clang)
+  end
+
+  def test_apple_gnu_libstdcxx_incompatibility
+    assert !@clang.compatible_with?(@gcc48)
+    assert !@gcc48.compatible_with?(@clang)
+  end
+
+  def test_gnu_cross_version_incompatibility
+    assert !@clang.compatible_with?(@gcc48)
+    assert !@gcc48.compatible_with?(@clang)
+  end
+
+  def test_libstdcxx_libcxx_incompatibility
+    assert !@clang.compatible_with?(@lcxx)
+    assert !@lcxx.compatible_with?(@clang)
+  end
+
+  def test_apple_compiler_reporting
+    assert @clang.apple_compiler?
+    assert @gcc.apple_compiler?
+    assert @llvm.apple_compiler?
+    assert @gcc4.apple_compiler?
+    assert !@gcc48.apple_compiler?
+  end
+
+  def test_type_string_formatting
+    assert_equal @clang.type_string, 'libstdc++'
+    assert_equal @lcxx.type_string, 'libc++'
+  end
+
+  def test_constructing_from_tab
+    stdlib = Tab.dummy_tab.cxxstdlib
+    assert_equal stdlib.compiler, :clang
+    assert_equal stdlib.type, :libstdcxx
+  end
+end