[Sandbox] Use the realpath of the root.

Fixes pod lib lint
Closes #1566

CHANGELOG.md

@@ -6,6 +6,11 @@ To install or update CocoaPods see this [guide](http://docs.cocoapods.org/guides
 
 ###### Bug Fixes
 
+* Fixed a bug which resulted in `pod lib lint` not being able to find the
+  headers.  
+  [Fabio Pelosin](https://github.com/irrationalfab)
+  [#1566](https://github.com/CocoaPods/CocoaPods/issues/1566)
+
 * Fixed the developer frameworks search paths so that
   `$(SDKROOT)/Developer/Library/Frameworks` is used for iOS and
   `$(DEVELOPER_LIBRARY_DIR)/Frameworks` is used for OS X  

lib/cocoapods/sandbox.rb

@@ -62,13 +62,13 @@ module Pod
     # @param [String, Pathname] root @see root
     #
     def initialize(root)
-      @root = Pathname.new(root)
+      FileUtils.mkdir_p(root)
+      @root = Pathname.new(root).realpath
       @public_headers = HeadersStore.new(self, "Headers")
       @predownloaded_pods = []
       @head_pods = []
       @checkout_sources = {}
       @development_pods = {}
-      FileUtils.mkdir_p(@root)
     end
 
     # @return [Lockfile] the manifest which contains the information about the

lib/cocoapods/sandbox/headers_store.rb

@@ -9,7 +9,7 @@ module Pod
       # @return [Pathname] the absolute path of this header directory.
       #
       def root
-        @sandbox.root + @relative_path
+        @root ||= @sandbox.root + @relative_path
       end
 
       # @return [Sandbox] the sandbox where this header directory is stored.
@@ -70,7 +70,8 @@ module Pod
         namespaced_path.mkpath unless File.exist?(namespaced_path)
 
         relative_header_paths.map do |relative_header_path|
-          source = (@sandbox.root + relative_header_path).relative_path_from(namespaced_path)
+          absolute_source = (@sandbox.root + relative_header_path)
+          source = absolute_source.relative_path_from(namespaced_path)
           Dir.chdir(namespaced_path) do
             FileUtils.ln_sf(source, relative_header_path.basename)
           end

spec/unit/sandbox_spec.rb

@@ -11,6 +11,15 @@ module Pod
 
     describe "In general" do
 
+      it "reads the real path of the root so it can be used to build relative paths" do
+        root_realpath = temporary_directory + 'Folder/SubFolder'
+        FileUtils.mkdir_p(root_realpath)
+        symlink = temporary_directory + 'symlink'
+        File.symlink(root_realpath, symlink)
+        sandbox = Pod::Sandbox.new(symlink + 'Sandbox')
+        sandbox.root.to_s.should.end_with 'Folder/SubFolder/Sandbox'
+      end
+
       it "automatically creates its root if it doesn't exist" do
         File.directory?(temporary_directory + 'Sandbox').should.be.true
       end