Disable libSystem objects for ARC libs that target older platforms.

This applies when the deployment target is set to < iOS 6.0 or
OS X 10.8, or not specified at all.

lib/cocoapods/specification.rb

@@ -319,9 +319,49 @@ module Pod
       @parent ? @parent.recursive_compiler_flags | @compiler_flags[active_platform] : @compiler_flags[active_platform]
     end
 
+    ENABLE_OBJECT_USE_OBJC_FROM = {
+      :ios => Version.new('6'),
+      :osx => Version.new('10.8')
+    }
+
+    # The following behavior is regarding the `OS_OBJECT_USE_OBJC` flag. When
+    # set to `0`, it will allow code to use `dispatch_release()` on >= iOS 6.0
+    # and OS X 10.8.
+    #
+    # * New libraries that do *not* require ARC don’t need to care about this
+    #   issue at all.
+    #
+    # * New libraries that *do* require ARC _and_ have a deployment target of
+    #   >= iOS 6.0 or OS X 10.8:
+    #
+    #   These no longer use `dispatch_release()` and should *not* have the
+    #   `OS_OBJECT_USE_OBJC` flag set to `0`.
+    #
+    #   **Note:** this means that these libraries *have* to specify the
+    #             deployment target in order to function well.
+    #
+    # * New libraries that *do* require ARC, but have a deployment target of
+    #   < iOS 6.0 or OS X 10.8:
+    #
+    #   These contain `dispatch_release()` calls and as such need the
+    #   `OS_OBJECT_USE_OBJC` flag set to `1`.
+    #
+    #   **Note:** libraries that do *not* specify a platform version are
+    #             assumed to have a deployment target of < iOS 6.0 or OS X 10.8.
+    #
+    # For more information, see: http://opensource.apple.com/source/libdispatch/libdispatch-228.18/os/object.h
+    #
     def compiler_flags
       flags = recursive_compiler_flags.dup
-      flags << '-fobjc-arc' if requires_arc
+      if requires_arc
+        flags << '-fobjc-arc'
+        ios_target, osx_target = deployment_target(:ios), deployment_target(:osx)
+        if (ios_target.nil? && osx_target.nil?) ||
+            (ios_target && Version.new(ios_target) < ENABLE_OBJECT_USE_OBJC_FROM[:ios]) ||
+             (osx_target && Version.new(osx_target) < ENABLE_OBJECT_USE_OBJC_FROM[:osx])
+          flags << '-DOS_OBJECT_USE_OBJC=0'
+        end
+      end
       flags.join(' ')
     end
 

spec/unit/specification_spec.rb

@@ -107,11 +107,11 @@ describe "A Pod::Specification loaded from a podspec" do
   it "adds compiler flags if ARC is required" do
     @spec.parent.should == nil
     @spec.requires_arc = true
-    @spec.activate_platform(:ios).compiler_flags.should == "-fobjc-arc"
-    @spec.activate_platform(:osx).compiler_flags.should == "-fobjc-arc"
+    @spec.activate_platform(:ios).compiler_flags.should == "-fobjc-arc -DOS_OBJECT_USE_OBJC=0"
+    @spec.activate_platform(:osx).compiler_flags.should == "-fobjc-arc -DOS_OBJECT_USE_OBJC=0"
     @spec.compiler_flags = "-Wunused-value"
-    @spec.activate_platform(:ios).compiler_flags.should == "-Wunused-value -fobjc-arc"
-    @spec.activate_platform(:osx).compiler_flags.should == "-Wunused-value -fobjc-arc"
+    @spec.activate_platform(:ios).compiler_flags.should == "-Wunused-value -fobjc-arc -DOS_OBJECT_USE_OBJC=0"
+    @spec.activate_platform(:osx).compiler_flags.should == "-Wunused-value -fobjc-arc -DOS_OBJECT_USE_OBJC=0"
   end
 end
 
@@ -523,7 +523,7 @@ describe "A Pod::Specification, concerning its attributes that support different
     end
 
     it "returns the same list of compiler flags for each platform" do
-      compiler_flags = '-Wdeprecated-implementations -fobjc-arc'
+      compiler_flags = '-Wdeprecated-implementations -fobjc-arc -DOS_OBJECT_USE_OBJC=0'
       @spec.activate_platform(:ios).compiler_flags.should == compiler_flags
       @spec.activate_platform(:osx).compiler_flags.should == compiler_flags
     end
@@ -587,8 +587,8 @@ describe "A Pod::Specification, concerning its attributes that support different
     end
 
     it "returns the same list of compiler flags for each platform" do
-      @spec.activate_platform(:ios).compiler_flags.should == '-Wdeprecated-implementations -fobjc-arc'
-      @spec.activate_platform(:osx).compiler_flags.should == '-Wfloat-equal -fobjc-arc'
+      @spec.activate_platform(:ios).compiler_flags.should == '-Wdeprecated-implementations -fobjc-arc -DOS_OBJECT_USE_OBJC=0'
+      @spec.activate_platform(:osx).compiler_flags.should == '-Wfloat-equal -fobjc-arc -DOS_OBJECT_USE_OBJC=0'
     end
 
     it "returns the same list of dependencies for each platform" do
@@ -596,4 +596,42 @@ describe "A Pod::Specification, concerning its attributes that support different
       @spec.activate_platform(:osx).dependencies.should == [Pod::Dependency.new('SSZipArchive')]
     end
   end
+
+  describe "concerning ARC before and after iOS 6.0 and OS X 10.8" do
+    before do
+      @spec = Pod::Spec.new
+    end
+
+    it "does not do anything if ARC is *not* required" do
+      @spec.ios.deployment_target = '5'
+      @spec.osx.deployment_target = '10.6'
+      [:ios, :osx, [:ios, '6'], [:ios, '6.1'], [:osx, '10.8'], [:osx, '10.8.2']].each do |target|
+        @spec.activate_platform(*target).compiler_flags.should.not.include '-DOS_OBJECT_USE_OBJC'
+      end
+    end
+
+    it "does *not* disable the `OS_OBJECT_USE_OBJC` flag if ARC is required and has a deployment target of >= iOS 6.0 or OS X 10.8" do
+      @spec.ios.deployment_target = '6'
+      @spec.osx.deployment_target = '10.8'
+      [[:ios, '6'], [:ios, '6.1'], [:osx, '10.8'], [:osx, '10.8.2']].each do |target|
+        @spec.activate_platform(*target).compiler_flags.should.not.include '-DOS_OBJECT_USE_OBJC'
+      end
+    end
+
+    it "*does* disable the `OS_OBJECT_USE_OBJC` flag if ARC is required but has a deployment target < iOS 6.0 or OS X 10.8" do
+      @spec.requires_arc = true
+      @spec.ios.deployment_target = '5.1'
+      @spec.osx.deployment_target = '10.7.2'
+      [[:ios, '6'], [:ios, '6.1'], [:osx, '10.8'], [:osx, '10.8.2']].each do |target|
+        @spec.activate_platform(*target).compiler_flags.should.include '-DOS_OBJECT_USE_OBJC=0'
+      end
+    end
+
+    it "*does* disable the `OS_OBJECT_USE_OBJC` flag if ARC is required and *no* deployment target is specified" do
+      @spec.requires_arc = true
+      [:ios, :osx, [:ios, '6'], [:ios, '6.1'], [:osx, '10.8'], [:osx, '10.8.2']].each do |target|
+        @spec.activate_platform(*target).compiler_flags.should.include '-DOS_OBJECT_USE_OBJC=0'
+      end
+    end
+  end
 end