accomidate hardlinks properly

now with tests

ensure the destination folder is created for travis

create destination for hard link file_syncer spec

more test fixing

lib/omnibus/file_syncer.rb

@@ -101,16 +101,28 @@ module Omnibus
             FileUtils.ln_sf(target, "#{destination}/#{relative_path}")
           end
         when :file
-          # First attempt a regular copy. If we don't have write
-          # permission on the File, open will probably fail with
-          # EACCES (making it hard to sync files with permission
-          # r--r--r--). Rescue this error and use cp_r's
-          # :remove_destination option.
-          begin
-            FileUtils.cp(source_file, "#{destination}/#{relative_path}")
-          rescue Errno::EACCES
-            FileUtils.cp_r(source_file, "#{destination}/#{relative_path}",
-                           :remove_destination => true)
+          source_stat = File.stat(source_file)
+          # Detect 'files' which are hard links and use ln instead of cp to
+          # duplicate them, provided their source is in place already
+          if hardlink? source_stat
+            if existing = hardlink_sources[[source_stat.dev, source_stat.ino]]
+              FileUtils.ln(existing, "#{destination}/#{relative_path}")
+            else
+              FileUtils.cp(source_file, "#{destination}/#{relative_path}")
+              hardlink_sources.store([source_stat.dev, source_stat.ino], "#{destination}/#{relative_path}")
+            end
+          else
+            # First attempt a regular copy. If we don't have write
+            # permission on the File, open will probably fail with
+            # EACCES (making it hard to sync files with permission
+            # r--r--r--). Rescue this error and use cp_r's
+            # :remove_destination option.
+            begin
+              FileUtils.cp(source_file, "#{destination}/#{relative_path}")
+            rescue Errno::EACCES
+              FileUtils.cp_r(source_file, "#{destination}/#{relative_path}",
+                             :remove_destination => true)
+            end
           end
         else
           raise RuntimeError,
@@ -155,5 +167,34 @@ module Omnibus
     def relative_path_for(path, parent)
       Pathname.new(path).relative_path_from(Pathname.new(parent)).to_s
     end
+
+    #
+    # A list of hard link file(s) sources which have already been copied,
+    # indexed by device and inode number.
+    #
+    # @api private
+    #
+    # @return [Hash{Array<FixNum, FixNum> => String}]
+    #
+    def hardlink_sources
+      @hardlink_sources ||= {}
+    end
+
+    #
+    # Determines whether or not a file is a hardlink.
+    #
+    # @param [File::Stat] stat
+    #   the File::Stat object for a file you wand to test
+    #
+    # @return [true, false]
+    #
+    def hardlink?(stat)
+      case stat.ftype.to_sym
+      when :file
+        stat.nlink > 1
+      else
+        false
+      end
+    end
   end
 end

spec/functional/file_syncer_spec.rb

@@ -101,6 +101,30 @@ module Omnibus
         end
       end
+      context 'when target files are hard links' do
+        let(:source) do
+          source = File.join(tmp_path, 'source')
+          FileUtils.mkdir_p(source)
+
+          create_directory(source, 'bin')
+               create_file(source, 'bin', 'git')
+               FileUtils.ln("#{source}/bin/git", "#{source}/bin/git-tag")
+               FileUtils.ln("#{source}/bin/git", "#{source}/bin/git-write-tree")
+
+          source
+        end
+
+        it 'copies the first instance and links to that instance thereafter' do
+          FileUtils.mkdir_p("#{destination}/bin")
+
+          described_class.sync(source, destination)
+
+          expect("#{destination}/bin/git").to be_a_file
+          expect("#{destination}/bin/git-tag").to be_a_hardlink
+          expect("#{destination}/bin/git-write-tree").to be_a_hardlink
+        end
+      end
+
       context 'with deeply nested paths and symlinks' do
         let(:source) do
           source = File.join(tmp_path, 'source')

spec/support/matchers.rb

@@ -34,3 +34,10 @@ RSpec::Matchers.define :be_an_executable do
     File.executable?(actual)
   end
 end
+
+# expect('/path/to/file').to be_a_hardlink
+RSpec::Matchers.define :be_a_hardlink do |path|
+  match do |actual|
+    File.stat(actual).nlink > 2
+  end
+end