Backport 'Rebase' feature from EE to CEjprovazn-rebase

When a project uses fast-forward merging strategy user has
to rebase MRs to target branch before it can be merged.
Now user can do rebase in UI by clicking 'Rebase' button
instead of doing rebase locally.

This feature was already present in EE, this is only backport
of the feature to CE. Couple of changes:
* removed rebase license check
* renamed migration (changed timestamp)

Closes #40301

2 files changed, 54 insertions, 0 deletions

diff --git a/app/services/merge_requests/rebase_service.rb b/app/services/merge_requests/rebase_service.rb
new file mode 100644
index 00000000000..0d5a25fa28e
--- /dev/null
+++ b/app/services/merge_requests/rebase_service.rb
@@ -0,0 +1,30 @@
+module MergeRequests
+  class RebaseService < MergeRequests::WorkingCopyBaseService
+    def execute(merge_request)
+      @merge_request = merge_request
+
+      if rebase
+        success
+      else
+        error('Failed to rebase. Should be done manually')
+      end
+    end
+
+    def rebase
+      if merge_request.rebase_in_progress?
+        log_error('Rebase task canceled: Another rebase is already in progress', save_message_on_model: true)
+        return false
+      end
+
+      rebase_sha = repository.rebase(current_user, merge_request)
+
+      merge_request.update_attributes(rebase_commit_sha: rebase_sha)
+
+      true
+    rescue => e
+      log_error('Failed to rebase branch:')
+      log_error(e.message, save_message_on_model: true)
+      false
+    end
+  end
+end
diff --git a/app/services/merge_requests/working_copy_base_service.rb b/app/services/merge_requests/working_copy_base_service.rb
new file mode 100644
index 00000000000..186e05bf966
--- /dev/null
+++ b/app/services/merge_requests/working_copy_base_service.rb
@@ -0,0 +1,24 @@
+module MergeRequests
+  class WorkingCopyBaseService < MergeRequests::BaseService
+    attr_reader :merge_request
+
+    def source_project
+      @source_project ||= merge_request.source_project
+    end
+
+    def target_project
+      @target_project ||= merge_request.target_project
+    end
+
+    def log_error(message, save_message_on_model: false)
+      Gitlab::GitLogger.error("#{self.class.name} error (#{merge_request.to_reference(full: true)}): #{message}")
+
+      merge_request.update(merge_error: message) if save_message_on_model
+    end
+
+    # Don't try to print expensive instance variables.
+    def inspect
+      "#<#{self.class} #{merge_request.to_reference(full: true)}>"
+    end
+  end
+end