[PodfileValidator] Validate there are no duplicate targets in the Podfile

lib/cocoapods/installer/podfile_validator.rb

@@ -34,6 +34,7 @@ module Pod
         validate_pod_directives
         validate_no_abstract_only_pods!
         validate_dependencies_are_present!
+        validate_no_duplicate_targets!
 
         @validated = true
       end
@@ -122,6 +123,16 @@ module Pod
           add_error "The dependency `#{dep}` is not used in any concrete target."
         end
       end
+
+      def validate_no_duplicate_targets!
+        podfile.target_definition_list.group_by { |td| [td.name, td.user_project_path] }.
+          each do |(name, project), definitions|
+          next unless definitions.size > 1
+          error = "The target `#{name}` is declared twice"
+          error << " for the project `#{project}`" if project
+          add_error(error << '.')
+        end
+      end
     end
   end
 end

spec/unit/installer/podfile_validator_spec.rb

@@ -182,5 +182,54 @@ module Pod
         validator.errors.should.be.empty
       end
     end
+
+    describe 'duplicated targets' do
+      it 'errors when the same target is declared twice' do
+        podfile = Pod::Podfile.new do
+          pod 'Alamofire'
+          target 'Target'
+          target 'Target'
+        end
+        validator = Installer::PodfileValidator.new(podfile)
+        validator.validate
+
+        validator.should.not.be.valid
+        validator.errors.should == ['The target `Target` is declared twice.']
+      end
+
+      it 'errors when the same target is declared twice when using a custom xcodeproj' do
+        podfile = Pod::Podfile.new do
+          pod 'Alamofire'
+          target 'Target' do
+            xcodeproj 'Project.xcodeproj'
+          end
+          target 'Target' do
+            xcodeproj 'Project.xcodeproj'
+          end
+        end
+        validator = Installer::PodfileValidator.new(podfile)
+        validator.validate
+
+        validator.should.not.be.valid
+        validator.errors.should == ['The target `Target` is declared twice for the project `Project.xcodeproj`.']
+      end
+
+      it 'does not error when the same target is declared twice for different projects' do
+        podfile = Pod::Podfile.new do
+          pod 'Alamofire'
+          target 'Target' do
+            xcodeproj 'Project.xcodeproj'
+          end
+          target 'Target' do
+            xcodeproj 'Project 1.xcodeproj'
+          end
+          target 'Target'
+        end
+        validator = Installer::PodfileValidator.new(podfile)
+        validator.validate
+
+        validator.should.be.valid
+      end
+    end
   end
 end