[UserProjectIntegrator] Check if the xcconfig files is overridden.

Closes #92.

CHANGELOG.md

 ## Master
 [CocoaPods](https://github.com/CocoaPods/CocoaPods/compare/0.12.0...master)
 
+###### Enhancements
+
+- Check if any of the build settings defined in the xcconfig files is overridden. [#92](https://github.com/CocoaPods/CocoaPods/issues/92)
+
 ###### Bug fixes
 
 - The final project isn’t affected anymore by the `inhibit_all_warnings!` option.

lib/cocoapods/installer/target_installer.rb

@@ -105,6 +105,8 @@ module Pod
         end
         puts "- Generating xcconfig file at `#{sandbox.root + @target_definition.xcconfig_name}'" if config.verbose?
         xcconfig.save_as(sandbox.root + @target_definition.xcconfig_name)
+        @target_definition.xcconfig = xcconfig
+
         puts "- Generating prefix header at `#{sandbox.root + @target_definition.prefix_header_name}'" if config.verbose?
         save_prefix_header_as(sandbox.root + @target_definition.prefix_header_name, pods)
         puts "- Generating copy resources script at `#{sandbox.root + @target_definition.copy_resources_script_name}'" if config.verbose?

lib/cocoapods/installer/user_project_integrator.rb

@@ -135,9 +135,28 @@ module Pod
         def add_xcconfig_base_configuration
           xcconfig = user_project.files.new('path' => @target_definition.xcconfig_relative_path)
           targets.each do |target|
+            config_build_names_by_overriden_key = {}
             target.build_configurations.each do |config|
+              config_name = config.attributes["name"]
+              if @target_definition.xcconfig
+                @target_definition.xcconfig.attributes.each do |key, value|
+                  target_value = config.build_settings[key]
+                  if target_value && !target_value.include?('$(inherited)')
+                    config_build_names_by_overriden_key[key] ||= []
+                    config_build_names_by_overriden_key[key] << config_name
+                  end
+                end
+              end
+
               config.base_configuration = xcconfig
             end
+
+            config_build_names_by_overriden_key.each do |key, config_build_names|
+              name = "#{target.attributes["name"]} [#{config_build_names.join(' - ')}]"
+              puts "\n[!] The target `#{name}' overrides the `#{key}' build setting defined in `#{@target_definition.xcconfig_relative_path}'.".yellow
+              puts "    - Use the `$(inherited)' flag, or"
+              puts "    - Remove the build settings from the target."
+            end
           end
         end
 

lib/cocoapods/podfile.rb

@@ -143,6 +143,8 @@ module Pod
         relative_to_srcroot("Pods/#{xcconfig_name}").to_s
       end
 
+      attr_accessor :xcconfig
+
       def copy_resources_script_name
         "#{label}-resources.sh"
       end