Support merge to ref for merge-commit and squash

Adds the ground work for writing into
the merge ref refs/merge-requests/:iid/merge the
merge result between source and target branches of
a MR, without further side-effects such as
mailing, MR updates and target branch changes.

3 files changed, 28 insertions, 0 deletions

diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 75fca96ce0a..1468ae1c34a 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -764,6 +764,16 @@ class MergeRequest < ActiveRecord::Base
     true
   end
 
+  def mergeable_to_ref?
+    return false if merged?
+    return false if broken?
+
+    # Given the `merge_ref_path` will have the same
+    # state the `target_branch` would have. Ideally
+    # we need to check if it can be merged to it.
+    project.repository.can_be_merged?(diff_head_sha, target_branch)
+  end
+
   def ff_merge_possible?
     project.repository.ancestor?(target_branch_sha, diff_head_sha)
   end
@@ -1077,6 +1087,10 @@ class MergeRequest < ActiveRecord::Base
     "refs/#{Repository::REF_MERGE_REQUEST}/#{iid}/head"
   end
 
+  def merge_ref_path
+    "refs/#{Repository::REF_MERGE_REQUEST}/#{iid}/merge"
+  end
+
   def in_locked_state
     begin
       lock_mr
diff --git a/app/models/project.rb b/app/models/project.rb
index 83f8d004a46..889572e693a 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -1925,6 +1925,14 @@ class Project < ActiveRecord::Base
     persisted? && path_changed?
   end
 
+  def human_merge_method
+    if merge_method == :ff
+      'Fast-forward'
+    else
+      merge_method.to_s.humanize
+    end
+  end
+
   def merge_method
     if self.merge_requests_ff_only_enabled
       :ff
diff --git a/app/models/repository.rb b/app/models/repository.rb
index ed55a6e572b..cd761a29618 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -854,6 +854,12 @@ class Repository
     end
   end
 
+  def merge_to_ref(user, source_sha, merge_request, target_ref, message)
+    branch = merge_request.target_branch
+
+    raw.merge_to_ref(user, source_sha, branch, target_ref, message)
+  end
+
   def ff_merge(user, source, target_branch, merge_request: nil)
     their_commit_id = commit(source)&.id
     raise 'Invalid merge source' if their_commit_id.nil?