No pod target if `source_files` only has headers.

This allows "fake" frameworks and static libraries to be linked directly
against the user target, avoiding symbol reexport problems when
integrating as frameworks. It also applies to integration as static
libraries to reduce build times by not creating unnecessary targets.

CHANGELOG.md

@@ -33,6 +33,10 @@ To install release candidates run `[sudo] gem install cocoapods --pre`
   [Samuel Giddins](https://github.com/segiddins)
   [#3101](https://github.com/CocoaPods/CocoaPods/issues/3101)
 
+* Do not create pod target if `source_files` only contains headers.  
+  [Boris Bügling](https://github.com/neonichu)
+  [#3106](https://github.com/CocoaPods/CocoaPods/issues/3106)
+
 
 ## 0.37.0.beta.1
 

lib/cocoapods/target/pod_target.rb

@@ -52,7 +52,9 @@ module Pod
     # A target should not be build if it has no source files.
     #
     def should_build?
-      !file_accessors.flat_map(&:source_files).empty?
+      source_files = file_accessors.flat_map(&:source_files)
+      source_files -= file_accessors.flat_map(&:headers)
+      !source_files.empty?
     end
 
     # @return [Array<Specification::Consumer>] the specification consumers for

spec/unit/target/pod_target_spec.rb

@@ -63,6 +63,22 @@ module Pod
         end.message
         message.should.match /subspecs across different build configurations/
       end
+
+      it 'builds a pod target if there are actual source files' do
+        fa = Sandbox::FileAccessor.new(nil, @pod_target)
+        fa.stubs(:source_files).returns([Pathname.new('foo.m')])
+        @pod_target.stubs(:file_accessors).returns([fa])
+
+        @pod_target.should_build?.should == true
+      end
+
+      it 'does not build a pod target if there are only header files' do
+        fa = Sandbox::FileAccessor.new(nil, @pod_target)
+        fa.stubs(:source_files).returns([Pathname.new('foo.h')])
+        @pod_target.stubs(:file_accessors).returns([fa])
+
+        @pod_target.should_build?.should == false
+      end
     end
 
     describe 'Support files' do