fix(diff): Support files renaming between revisions for a diff

Solves #1

Author: edeweerd1A

lib/asciidoctor-git-include.rb

@@ -16,10 +16,11 @@ def process doc, reader, target, attributes
     lines = attributes.fetch('lines', '')
     as_diff = attributes.value?('diff') || attributes.key?('diff')
     diff_revision = attributes.fetch('diff', "#{revision}~1")
+    target_before = attributes.fetch('difftarget', target)
 
     cmd = %(git -C #{repository} show #{revision}:#{target})
     if (as_diff)
-      cmd = %(git -C #{repository} diff #{diff_revision}:#{target} #{revision}:#{target})
+      cmd = %(git -C #{repository} diff #{diff_revision}:#{target_before} #{revision}:#{target})
     end
     content = %x(#{cmd})
 

test/extension_test.rb

@@ -105,6 +105,18 @@ class ExtensionTest < Minitest::Test
       assert_match(/-messages = \["Hello"\]/, output)
       assert_match(/\+messages = \["Hello", "World", "!!!"\]/, output)
     end
+
+    test 'it includes a diff for specific revisions of a file that is renamed' do
+      input = <<-EOS
+include::git@test/fixtures/file-after-rename.adoc[revision=28c4082,diff=6d5eaf1,difftarget=test/fixtures/file-before-rename.adoc]
+      EOS
+
+      output = render_embedded_string input
+
+      assert_match(/diff --git a\/test\/fixtures\/file-before-rename.adoc b\/test\/fixtures\/file-after-rename.adoc/, output)
+      assert_match(/-Contents before rename./, output)
+      assert_match(/\+Contents after rename./, output)
+    end
   end
 
   def given_file_committed_to_fresh_repo(file_name, content)