Check for conflicts before creating target branch.

app/models/repository.rb

@@ -654,11 +654,28 @@ class Repository
     end
   end
 
-  def revert(user, commit, base_branch, target_branch = nil)
-    source_sha    = find_branch(base_branch).target
-    target_branch ||= base_branch
-    args          = [commit.id, source_sha]
-    args          << { mainline: 1 } if commit.merge_commit?
+  def revert(user, commit, base_branch, revert_tree_id = nil)
+    source_sha = find_branch(base_branch).target
+    revert_tree_id = check_revert_content(commit, base_branch) unless revert_tree_id
+
+    return false unless revert_tree_id
+
+    commit_with_hooks(user, base_branch) do |ref|
+      committer = user_to_committer(user)
+      source_sha = Rugged::Commit.create(rugged,
+        message: commit.revert_message,
+        author: committer,
+        committer: committer,
+        tree: revert_tree_id,
+        parents: [rugged.lookup(source_sha)],
+        update_ref: ref)
+    end
+  end
+
+  def check_revert_content(commit, base_branch)
+    source_sha = find_branch(base_branch).target
+    args       = [commit.id, source_sha]
+    args       << { mainline: 1 } if commit.merge_commit?
 
     revert_index = rugged.revert_commit(*args)
     return false if revert_index.conflicts?
@@ -666,16 +683,7 @@ class Repository
     tree_id = revert_index.write_tree(rugged)
     return false unless diff_exists?(source_sha, tree_id)
 
-    commit_with_hooks(user, target_branch) do |ref|
-      committer = user_to_committer(user)
-      source_sha = Rugged::Commit.create(rugged,
-        message: commit.revert_message,
-        author: committer,
-        committer: committer,
-        tree: tree_id,
-        parents: [rugged.lookup(source_sha)],
-        update_ref: ref)
-    end
+    tree_id
   end
 
   def diff_exists?(sha1, sha2)

app/services/commits/revert_service.rb

@@ -17,28 +17,28 @@ module Commits
 
     def commit
       revert_into = @create_merge_request ? @commit.revert_branch_name : @target_branch
+      revert_tree_id = repository.check_revert_content(@commit, @target_branch)
 
-      if @create_merge_request
-        # Temporary branch exists and contains the revert commit
-        return success if repository.find_branch(revert_into)
+      if revert_tree_id
+        create_target_branch(revert_into) if @create_merge_request
 
-        create_target_branch
-      end
-
-      unless repository.revert(current_user, @commit, revert_into)
+        repository.revert(current_user, @commit, revert_into, revert_tree_id)
+        success
+      else
         error_msg = "Sorry, we cannot revert this #{params[:revert_type_title]} automatically.
                      It may have already been reverted, or a more recent commit may have updated some of its content."
         raise ReversionError, error_msg
       end
-
-      success
     end
 
     private
 
-    def create_target_branch
+    def create_target_branch(new_branch)
+      # Temporary branch exists and contains the revert commit
+      return success if repository.find_branch(new_branch)
+
       result = CreateBranchService.new(@project, current_user)
-                                  .execute(@commit.revert_branch_name, @target_branch, source_project: @source_project)
+                                  .execute(new_branch, @target_branch, source_project: @source_project)
 
       if result[:status] == :error
         raise ReversionError, "There was an error creating the source branch: #{result[:message]}"