Add support for patch link extension for commit links on GFM

app/models/commit.rb

@@ -30,6 +30,8 @@ class Commit
   MIN_SHA_LENGTH = Gitlab::Git::Commit::MIN_SHA_LENGTH
   COMMIT_SHA_PATTERN = /\h{#{MIN_SHA_LENGTH},40}/.freeze
+  # Used by GFM to match and present link extensions on node texts and hrefs.
+  LINK_EXTENSION_PATTERN = /(patch)/.freeze
   def banzai_render_context(field)
     pipeline = field == :description ? :commit_description : :single_line
@@ -143,7 +145,8 @@ class Commit
   end
   def self.link_reference_pattern
-    @link_reference_pattern ||= super("commit", /(?<commit>#{COMMIT_SHA_PATTERN})/)
+    @link_reference_pattern ||=
+      super("commit", /(?<commit>#{COMMIT_SHA_PATTERN})?(\.(?<extension>#{LINK_EXTENSION_PATTERN}))?/)
   end
   def to_reference(from = nil, full: false)

changelogs/unreleased/17939-osw-patch-support-gfm.yml

+---
+title: Add support for patch link extension for commit links on GitLab Flavored Markdown
+merge_request:
+author:
+type: added

lib/banzai/filter/abstract_reference_filter.rb

@@ -213,6 +213,10 @@ module Banzai
           extras << "comment #{$1}"
         end
+        extension = matches[:extension] if matches.names.include?("extension")
+
+        extras << extension if extension
+
         extras
       end

spec/lib/banzai/filter/commit_reference_filter_spec.rb

@@ -207,4 +207,35 @@ describe Banzai::Filter::CommitReferenceFilter do
       expect(reference_filter(act).to_html).to match(%r{<a.+>#{Regexp.escape(invalidate_reference(reference))}</a>})
     end
   end
+
+  context 'URL reference for a commit patch' do
+    let(:namespace) { create(:namespace) }
+    let(:project2)  { create(:project, :public, :repository, namespace: namespace) }
+    let(:commit)    { project2.commit }
+    let(:link)      { urls.project_commit_url(project2, commit.id) }
+    let(:extension) { '.patch' }
+    let(:reference) { link + extension }
+
+    it 'links to a valid reference' do
+      doc = reference_filter("See #{reference}")
+
+      expect(doc.css('a').first.attr('href'))
+        .to eq reference
+    end
+
+    it 'has valid text' do
+      doc = reference_filter("See #{reference}")
+
+      expect(doc.text).to eq("See #{commit.reference_link_text(project)} (patch)")
+    end
+
+    it 'does not link to patch when extension match is after the path' do
+      invalidate_commit_reference = reference_filter("#{link}/builds.patch")
+
+      doc = reference_filter("See (#{invalidate_commit_reference})")
+
+      expect(doc.css('a').first.attr('href')).to eq "#{link}/builds"
+      expect(doc.text).to eq("See (#{commit.reference_link_text(project)} (builds).patch)")
+    end
+  end
 end