feat(diff): give capability to ignore whitespaces and caret returns in a diff

Solves #2

Author: edeweerd1A

Diff for: README.adoc

@@ -39,6 +39,7 @@ Then, inside your AsciiDoc file, use an `include` statement like normal, pointin
 * `revision` - repository revision to use (default: `HEAD`)
 * `lines` - specify the lines to include (i.e. `lines=2..5;10;12`)
 * `diff` - include a patch for the given `revision`, or between two revisions (see examples)
+* `ignorewhitespaces` - whether to ignore whitespaces and newlines changes in an included patch
 
 // tag::examples[]
 
@@ -103,4 +104,12 @@ To generate a patch for changes between two revisions (b015e8dd and b015e8dd):
 \include::git@path/within/repo/file.rb[revision=b015e8dd,diff=0245ac72]
 ----
 
+=== Including a patch ignoring whitespaces
+
+To generate a patch for changes introduced in a specific revision (b015e8dd) but ignoring the changes related to whitespaces and caret line return:
+
+----
+\include::git@path/within/repo/file.rb[revision=b015e8dd,diff,ignorewhitespaces]
+----
+
 // end::examples[]

Diff for: 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")
+    ignore_whitespaces_option = attributes.value?('ignorewhitespaces') || attributes.key?('ignorewhitespaces') ? '--ignore-cr-at-eol --ignore-space-at-eol -w -b --ignore-blank-lines' : ''
 
     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 #{ignore_whitespaces_option} #{diff_revision}:#{target} #{revision}:#{target})
     end
     content = %x(#{cmd})
 

Diff for: test/extension_test.rb

@@ -105,6 +105,19 @@ class ExtensionTest < Minitest::Test
       assert_match(/-messages = \["Hello"\]/, output)
       assert_match(/\+messages = \["Hello", "World", "!!!"\]/, output)
     end
+
+    test 'it includes a diff ignoring whitespaces and caret returns' do
+      input = <<-EOS
+include::git@test/fixtures/lots_of_whitespaces.adoc[revision=e80ca3c,diff=2c2f9a9,ignorewhitespaces]
+      EOS
+
+      output = render_embedded_string input
+
+      assert_match(/diff --git a\/test\/fixtures\/lots_of_whitespaces.adoc b\/test\/fixtures\/lots_of_whitespaces.adoc/, output)
+      assert_match(/-Another line with more content/, output)
+      assert_match(/\+Another line with more content that has changed/, output)
+      refute_match(/-Some line with some content/, output)
+    end
   end
 
   def given_file_committed_to_fresh_repo(file_name, content)