[Frameworks] Fail lint for Swift on iOS < 8.

Have to use dynamic frameworks for Swift and they are unsupported on iOS
7.

CHANGELOG.md

@@ -27,6 +27,10 @@ To install release candidates run `[sudo] gem install cocoapods --pre`
   `/tmp`.  
   [Samuel Giddins](https://github.com/segiddins)
 
+* Let lint fail for Swift pods supporting deployment targets below iOS 8.0.  
+  [Boris Bügling](https://github.com/neonichu)
+  [#2963](https://github.com/CocoaPods/CocoaPods/issues/2963)
+
 ##### Bug Fixes
 
 * Added support for .tpp C++ header files in specs (previously were getting

lib/cocoapods/validator.rb

@@ -310,6 +310,10 @@ module Pod
       installer.install!
 
       file_accessors = installer.aggregate_targets.map do |target|
+        if target.pod_targets.any?(&:uses_swift?) && deployment_target.to_f < 8.0
+          error('swift', 'Swift support uses dynamic frameworks and is therefore only supported on iOS > 8.')
+        end
+
         target.pod_targets.map(&:file_accessors)
       end.flatten
 

spec/unit/validator_spec.rb

@@ -440,6 +440,36 @@ module Pod
         validator.validated?.should.be.true
       end
     end
+
+    describe 'swift validation' do
+      def test_swiftpod
+        podspec = stub_podspec(/.*source_files.*/, '"source_files": "*.swift",')
+        podspec.gsub!(/.*license.*$/, '"license": "Public Domain",')
+        file = write_podspec(podspec)
+
+        Pod::Sandbox::FileAccessor.any_instance.stubs(:source_files).returns([Pathname.new('/Foo.swift')])
+        validator = Validator.new(file, SourcesManager.master.map(&:url))
+        validator.stubs(:build_pod)
+        validator.stubs(:validate_url)
+        validator.validate
+        validator
+      end
+
+      it 'fails on deployment target < iOS 8 for Swift Pods' do
+        validator = test_swiftpod
+
+        validator.results.map(&:to_s).first.should.match /dynamic frameworks.*iOS > 8/
+        validator.result_type.should == :error
+      end
+
+      it 'succeeds on deployment targets >= iOS 8 for Swift Pods' do
+        Specification.any_instance.stubs(:deployment_target).returns('9.0')
+
+        validator = test_swiftpod
+
+        validator.results.count.should == 0
+      end
+    end
     #-------------------------------------------------------------------------#
   end
 end