Add first_commit and first_multiline_commit to commit template

Changelog: added

app/graphql/types/merge_request_type.rb

@@ -96,7 +96,7 @@ module Types
           description: 'Rebase commit SHA of the merge request.'
     field :rebase_in_progress, GraphQL::Types::Boolean, method: :rebase_in_progress?, null: false, calls_gitaly: true,
           description: 'Indicates if there is a rebase currently in progress for the merge request.'
-    field :default_merge_commit_message, GraphQL::Types::String, null: true,
+    field :default_merge_commit_message, GraphQL::Types::String, null: true, calls_gitaly: true,
           description: 'Default merge commit message of the merge request.'
     field :default_merge_commit_message_with_description, GraphQL::Types::String, null: true,
           description: 'Default merge commit message of the merge request with description. Will have the same value as `defaultMergeCommitMessage` when project has `mergeCommitTemplate` set.',

doc/user/project/merge_requests/commit_templates.md

@@ -65,6 +65,9 @@ GitLab creates a squash commit message with this template:
 
 ## Supported variables in commit templates
 
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/20263) in GitLab 14.5.
+> - [Added](https://gitlab.com/gitlab-org/gitlab/-/issues/346805) `first_commit` and `first_multiline_commit` variables in GitLab 14.6.
+
 Commit message templates support these variables:
 
 | Variable | Description | Output example |
@@ -73,8 +76,10 @@ Commit message templates support these variables:
 | `%{target_branch}` | The name of the branch that the changes are applied to. | `main` |
 | `%{title}`         | Title of the merge request. | `Fix tests and translations` |
 | `%{issues}`        | String with phrase `Closes <issue numbers>`. Contains all issues mentioned in the merge request description that match [issue closing patterns](../issues/managing_issues.md#closing-issues-automatically). Empty if no issues are mentioned. | `Closes #465, #190 and #400` |
-| `%{description}`   | Description of the merge request. | `Merge request description.<br>Can be multiline.` |
+| `%{description}`   | Description of the merge request. | `Merge request description.`<br>`Can be multiline.` |
 | `%{reference}`     | Reference to the merge request. | `group-name/project-name!72359` |
+| `%{first_commit}`  | Full message of the first commit in merge request diff. | `Update README.md` |
+| `%{first_multiline_commit}` | Full message of the first commit that's not a merge commit and has more than one line in message body. Merge Request title if all commits aren't multiline. | `Update README.md`<br><br>`Improved project description in readme file.` |
 
 Empty variables that are the only word in a line are removed, along with all newline characters preceding it.
 

lib/gitlab/merge_requests/commit_message_generator.rb

@@ -35,7 +35,9 @@ module Gitlab
           "Closes #{closes_issues_references.to_sentence}"
         end,
         'description' => ->(merge_request) { merge_request.description.presence || '' },
-        'reference' => ->(merge_request) { merge_request.to_reference(full: true) }
+        'reference' => ->(merge_request) { merge_request.to_reference(full: true) },
+        'first_commit' => -> (merge_request) { merge_request.first_commit&.safe_message&.strip.presence || '' },
+        'first_multiline_commit' => -> (merge_request) { merge_request.first_multiline_commit&.safe_message&.strip.presence || merge_request.title }
       }.freeze
 
       PLACEHOLDERS_REGEX = Regexp.union(PLACEHOLDERS.keys.map do |key|

spec/lib/gitlab/merge_requests/commit_message_generator_spec.rb

@@ -16,6 +16,7 @@ RSpec.describe Gitlab::MergeRequests::CommitMessageGenerator do
   end
 
   let(:user) { project.creator }
+  let(:source_branch) { 'feature' }
   let(:merge_request_description) { "Merge Request Description\nNext line" }
   let(:merge_request_title) { 'Bugfix' }
   let(:merge_request) do
@@ -24,6 +25,8 @@ RSpec.describe Gitlab::MergeRequests::CommitMessageGenerator do
       :simple,
       source_project: project,
       target_project: project,
+      target_branch: 'master',
+      source_branch: source_branch,
       author: user,
       description: merge_request_description,
       title: merge_request_title
@@ -226,6 +229,50 @@ RSpec.describe Gitlab::MergeRequests::CommitMessageGenerator do
           MSG
         end
       end
+
+      context 'when project has merge commit template with first_commit' do
+        let(message_template_name) { <<~MSG.rstrip }
+          Message: %{first_commit}
+        MSG
+
+        it 'uses first commit' do
+          expect(result_message).to eq <<~MSG.rstrip
+            Message: Feature added
+
+            Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
+          MSG
+        end
+
+        context 'when branch has no unmerged commits' do
+          let(:source_branch) { 'v1.1.0' }
+
+          it 'is an empty string' do
+            expect(result_message).to eq 'Message: '
+          end
+        end
+      end
+
+      context 'when project has merge commit template with first_multiline_commit' do
+        let(message_template_name) { <<~MSG.rstrip }
+          Message: %{first_multiline_commit}
+        MSG
+
+        it 'uses first multiline commit' do
+          expect(result_message).to eq <<~MSG.rstrip
+            Message: Feature added
+
+            Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
+          MSG
+        end
+
+        context 'when branch has no multiline commits' do
+          let(:source_branch) { 'spooky-stuff' }
+
+          it 'is mr title' do
+            expect(result_message).to eq 'Message: Bugfix'
+          end
+        end
+      end
     end
   end
 

spec/models/merge_request_spec.rb

@@ -1648,6 +1648,9 @@ RSpec.describe MergeRequest, factory_default: :keep do
 
     it 'uses template from target project' do
       request = build(:merge_request, title: 'Fix everything')
+      request.compare_commits = [
+        double(safe_message: 'Commit message', gitaly_commit?: true, merge_commit?: false, description?: false)
+      ]
       subject.target_project.merge_commit_template = '%{title}'
 
       expect(request.default_merge_commit_message)