Pull common stdlib checking code into a method

Library/Homebrew/build.rb

@@ -182,25 +182,11 @@ class Build
 
   def detect_stdlibs
     keg = Keg.new(f.prefix)
-    # This first test includes executables because we still
-    # want to record the stdlib for something that installs no
-    # dylibs.
-    stdlibs = keg.detect_cxx_stdlibs
-    # This currently only tracks a single C++ stdlib per dep,
-    # though it's possible for different libs/executables in
-    # a given formula to link to different ones.
-    stdlib_in_use = CxxStdlib.create(stdlibs.first, ENV.compiler)
-    begin
-      stdlib_in_use.check_dependencies(f, deps)
-    rescue IncompatibleCxxStdlibs => e
-      opoo e.message
-    end
+    CxxStdlib.check_compatibility(f, deps, keg, ENV.compiler)
 
-    # This second check is recorded for checking dependencies,
-    # so executable are irrelevant at this point. If a piece
-    # of software installs an executable that links against libstdc++
-    # and dylibs against libc++, libc++-only dependencies can safely
-    # link against it.
+    # The stdlib recorded in the install receipt is used during dependency
+    # compatibility checks, so we only care about the stdlib that libraries
+    # link against.
     keg.detect_cxx_stdlibs(:skip_executables => true)
   end
 

Library/Homebrew/cxxstdlib.rb

@@ -11,6 +11,18 @@ class CxxStdlib
     klass.new(type, compiler)
   end
 
+  def self.check_compatibility(formula, deps, keg, compiler)
+    return if formula.skip_cxxstdlib_check?
+
+    stdlib = create(keg.detect_cxx_stdlibs.first, compiler)
+
+    begin
+      stdlib.check_dependencies(formula, deps)
+    rescue IncompatibleCxxStdlibs => e
+      opoo e.message
+    end
+  end
+
   attr_reader :type, :compiler
 
   def initialize(type, compiler)
@@ -32,17 +44,14 @@ class CxxStdlib
   end
 
   def check_dependencies(formula, deps)
-    unless formula.skip_cxxstdlib_check?
-      deps.each do |dep|
-        # Software is unlikely to link against anything from its
-        # buildtime deps, so it doesn't matter at all if they link
-        # against different C++ stdlibs
-        next if dep.build?
+    deps.each do |dep|
+      # Software is unlikely to link against libraries from build-time deps, so
+      # it doesn't matter if they link against different C++ stdlibs.
+      next if dep.build?
 
-        dep_stdlib = Tab.for_formula(dep.to_formula).cxxstdlib
-        if !compatible_with? dep_stdlib
-          raise IncompatibleCxxStdlibs.new(formula, dep, dep_stdlib, self)
-        end
+      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

Library/Homebrew/formula_installer.rb

@@ -158,13 +158,10 @@ class FormulaInstaller
         pour
         @poured_bottle = true
 
-        stdlibs = Keg.new(f.prefix).detect_cxx_stdlibs
-        stdlib_in_use = CxxStdlib.create(stdlibs.first, MacOS.default_compiler)
-        begin
-          stdlib_in_use.check_dependencies(f, f.recursive_dependencies)
-        rescue IncompatibleCxxStdlibs => e
-          opoo e.message
-        end
+        CxxStdlib.check_compatibility(
+          f, f.recursive_dependencies,
+          Keg.new(f.prefix), MacOS.default_compiler
+        )
 
         tab = Tab.for_keg f.prefix
         tab.poured_from_bottle = true