20 files changed, 626 insertions, 321 deletions

diff --git a/app/controllers/concerns/creates_commit.rb b/app/controllers/concerns/creates_commit.rb
index 6f43ce5226d..6286d67d30c 100644
--- a/app/controllers/concerns/creates_commit.rb
+++ b/app/controllers/concerns/creates_commit.rb
@@ -4,13 +4,15 @@ module CreatesCommit
   def create_commit(service, success_path:, failure_path:, failure_view: nil, success_notice: nil)
     set_commit_variables
 
+    start_branch = @mr_target_branch unless initial_commit?
     commit_params = @commit_params.merge(
-      source_project: @project,
-      source_branch: @ref,
-      target_branch: @target_branch
+      start_project: @mr_target_project,
+      start_branch: start_branch,
+      target_branch: @mr_source_branch
     )
 
-    result = service.new(@tree_edit_project, current_user, commit_params).execute
+    result = service.new(
+      @mr_source_project, current_user, commit_params).execute
 
     if result[:status] == :success
       update_flash_notice(success_notice)
@@ -89,20 +91,18 @@ module CreatesCommit
     @mr_source_project != @mr_target_project
   end
 
-  def different_branch?
-    @mr_source_branch != @mr_target_branch || different_project?
-  end
-
   def create_merge_request?
-    params[:create_merge_request].present? && different_branch?
+    # XXX: Even if the field is set, if we're checking the same branch
+    # as the target branch in the same project,
+    # we don't want to create a merge request.
+    params[:create_merge_request].present? &&
+      (different_project? || @ref != @target_branch)
   end
 
+  # TODO: We should really clean this up
   def set_commit_variables
-    @mr_source_branch ||= @target_branch
-
     if can?(current_user, :push_code, @project)
       # Edit file in this project
-      @tree_edit_project = @project
       @mr_source_project = @project
 
       if @project.forked?
@@ -112,15 +112,34 @@ module CreatesCommit
       else
         # Merge request to this project
         @mr_target_project = @project
-        @mr_target_branch ||= @ref
+        @mr_target_branch = @ref || @target_branch
       end
     else
-      # Edit file in fork
-      @tree_edit_project = current_user.fork_of(@project)
       # Merge request from fork to this project
-      @mr_source_project = @tree_edit_project
+      @mr_source_project = current_user.fork_of(@project)
       @mr_target_project = @project
-      @mr_target_branch ||= @ref
+      @mr_target_branch = @ref || @target_branch
     end
+
+    @mr_source_branch = guess_mr_source_branch
+  end
+
+  def initial_commit?
+    @mr_target_branch.nil? ||
+      !@mr_target_project.repository.branch_exists?(@mr_target_branch)
+  end
+
+  def guess_mr_source_branch
+    # XXX: Happens when viewing a commit without a branch. In this case,
+    # @target_branch would be the default branch for @mr_source_project,
+    # however we want a generated new branch here. Thus we can't use
+    # @target_branch, but should pass nil to indicate that we want a new
+    # branch instead of @target_branch.
+    return if
+      create_merge_request? &&
+          # XXX: Don't understand why rubocop prefers this indention
+          @mr_source_project.repository.branch_exists?(@target_branch)
+
+    @target_branch
   end
 end
diff --git a/app/controllers/projects/commit_controller.rb b/app/controllers/projects/commit_controller.rb
index c871043efbd..b5a7078a3a1 100644
--- a/app/controllers/projects/commit_controller.rb
+++ b/app/controllers/projects/commit_controller.rb
@@ -50,7 +50,7 @@ class Projects::CommitController < Projects::ApplicationController
   end
 
   def revert
-    assign_change_commit_vars(@commit.revert_branch_name)
+    assign_change_commit_vars
 
     return render_404 if @target_branch.blank?
 
@@ -59,7 +59,7 @@ class Projects::CommitController < Projects::ApplicationController
   end
 
   def cherry_pick
-    assign_change_commit_vars(@commit.cherry_pick_branch_name)
+    assign_change_commit_vars
 
     return render_404 if @target_branch.blank?
 
@@ -116,11 +116,9 @@ class Projects::CommitController < Projects::ApplicationController
     }
   end
 
-  def assign_change_commit_vars(mr_source_branch)
+  def assign_change_commit_vars
     @commit = project.commit(params[:id])
     @target_branch = params[:target_branch]
-    @mr_source_branch = mr_source_branch
-    @mr_target_branch = @target_branch
     @commit_params = {
       commit: @commit,
       create_merge_request: params[:create_merge_request].present? || different_project?
diff --git a/app/controllers/projects/compare_controller.rb b/app/controllers/projects/compare_controller.rb
index d32966645c8..321cde255c3 100644
--- a/app/controllers/projects/compare_controller.rb
+++ b/app/controllers/projects/compare_controller.rb
@@ -46,7 +46,8 @@ class Projects::CompareController < Projects::ApplicationController
   end
 
   def define_diff_vars
-    @compare = CompareService.new.execute(@project, @head_ref, @project, @start_ref)
+    @compare = CompareService.new(@project, @head_ref)
+      .execute(@project, @start_ref)
 
     if @compare
       @commits = @compare.commits
diff --git a/app/models/merge_request_diff.rb b/app/models/merge_request_diff.rb
index dadb81f9b6e..70bad2a4396 100644
--- a/app/models/merge_request_diff.rb
+++ b/app/models/merge_request_diff.rb
@@ -169,7 +169,8 @@ class MergeRequestDiff < ActiveRecord::Base
     # When compare merge request versions we want diff A..B instead of A...B
     # so we handle cases when user does squash and rebase of the commits between versions.
     # For this reason we set straight to true by default.
-    CompareService.new.execute(project, head_commit_sha, project, sha, straight: straight)
+    CompareService.new(project, head_commit_sha)
+      .execute(project, sha, straight: straight)
   end
 
   def commits_count
diff --git a/app/models/repository.rb b/app/models/repository.rb
index d77b7692d75..a54d75f7019 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -5,7 +5,7 @@ class Repository
 
   attr_accessor :path_with_namespace, :project
 
-  class CommitError < StandardError; end
+  CommitError = Class.new(StandardError)
 
   # Methods that cache data from the Git repository.
   #
@@ -64,10 +64,6 @@ class Repository
     @raw_repository ||= Gitlab::Git::Repository.new(path_to_repo)
   end
 
-  def update_autocrlf_option
-    raw_repository.autocrlf = :input if raw_repository.autocrlf != :input
-  end
-
   # Return absolute path to repository
   def path_to_repo
     @path_to_repo ||= File.expand_path(
@@ -168,63 +164,46 @@ class Repository
     tags.find { |tag| tag.name == name }
   end
 
-  def add_branch(user, branch_name, target)
-    oldrev = Gitlab::Git::BLANK_SHA
-    ref    = Gitlab::Git::BRANCH_REF_PREFIX + branch_name
-    target = commit(target).try(:id)
+  def add_branch(user, branch_name, ref)
+    newrev = commit(ref).try(:sha)
 
-    return false unless target
+    return false unless newrev
 
-    GitHooksService.new.execute(user, path_to_repo, oldrev, target, ref) do
-      update_ref!(ref, target, oldrev)
-    end
+    GitOperationService.new(user, self).add_branch(branch_name, newrev)
 
     after_create_branch
     find_branch(branch_name)
   end
 
   def add_tag(user, tag_name, target, message = nil)
-    oldrev = Gitlab::Git::BLANK_SHA
-    ref    = Gitlab::Git::TAG_REF_PREFIX + tag_name
-    target = commit(target).try(:id)
-
-    return false unless target
-
+    newrev = commit(target).try(:id)
     options = { message: message, tagger: user_to_committer(user) } if message
 
-    GitHooksService.new.execute(user, path_to_repo, oldrev, target, ref) do |service|
-      raw_tag = rugged.tags.create(tag_name, target, options)
-      service.newrev = raw_tag.target_id
-    end
+    return false unless newrev
+
+    GitOperationService.new(user, self).add_tag(tag_name, newrev, options)
 
     find_tag(tag_name)
   end
 
   def rm_branch(user, branch_name)
     before_remove_branch
-
     branch = find_branch(branch_name)
-    oldrev = branch.try(:dereferenced_target).try(:id)
-    newrev = Gitlab::Git::BLANK_SHA
-    ref    = Gitlab::Git::BRANCH_REF_PREFIX + branch_name
 
-    GitHooksService.new.execute(user, path_to_repo, oldrev, newrev, ref) do
-      update_ref!(ref, newrev, oldrev)
-    end
+    GitOperationService.new(user, self).rm_branch(branch)
 
     after_remove_branch
     true
   end
 
-  def rm_tag(tag_name)
+  def rm_tag(user, tag_name)
     before_remove_tag
+    tag = find_tag(tag_name)
 
-    begin
-      rugged.tags.delete(tag_name)
-      true
-    rescue Rugged::ReferenceError
-      false
-    end
+    GitOperationService.new(user, self).rm_tag(tag)
+
+    after_remove_tag
+    true
   end
 
   def ref_names
@@ -241,21 +220,6 @@ class Repository
     false
   end
 
-  def update_ref!(name, newrev, oldrev)
-    # We use 'git update-ref' because libgit2/rugged currently does not
-    # offer 'compare and swap' ref updates. Without compare-and-swap we can
-    # (and have!) accidentally reset the ref to an earlier state, clobbering
-    # commits. See also https://github.com/libgit2/libgit2/issues/1534.
-    command = %W(#{Gitlab.config.git.bin_path} update-ref --stdin -z)
-    _, status = Gitlab::Popen.popen(command, path_to_repo) do |stdin|
-      stdin.write("update #{name}\x00#{newrev}\x00#{oldrev}\x00")
-    end
-
-    return if status.zero?
-
-    raise CommitError.new("Could not update branch #{name.sub('refs/heads/', '')}. Please refresh and try again.")
-  end
-
   # Makes sure a commit is kept around when Git garbage collection runs.
   # Git GC will delete commits from the repository that are no longer in any
   # branches or tags, but we want to keep some of these commits around, for
@@ -435,6 +399,11 @@ class Repository
     repository_event(:remove_tag)
   end
 
+  # Runs code after removing a tag.
+  def after_remove_tag
+    expire_tags_cache
+  end
+
   def before_import
     expire_content_cache
   end
@@ -779,121 +748,132 @@ class Repository
     @tags ||= raw_repository.tags
   end
 
-  def commit_dir(user, path, message, branch, author_email: nil, author_name: nil)
-    update_branch_with_hooks(user, branch) do |ref|
-      options = {
-        commit: {
-          branch: ref,
-          message: message,
-          update_ref: false
-        }
-      }
-
-      options.merge!(get_committer_and_author(user, email: author_email, name: author_name))
-
-      raw_repository.mkdir(path, options)
-    end
-  end
-
-  def commit_file(user, path, content, message, branch, update, author_email: nil, author_name: nil)
-    update_branch_with_hooks(user, branch) do |ref|
-      options = {
-        commit: {
-          branch: ref,
-          message: message,
-          update_ref: false
-        },
-        file: {
-          content: content,
-          path: path,
-          update: update
-        }
-      }
-
-      options.merge!(get_committer_and_author(user, email: author_email, name: author_name))
+  # rubocop:disable Metrics/ParameterLists
+  def commit_dir(
+    user, path,
+    message:, branch_name:,
+    author_email: nil, author_name: nil,
+    start_branch_name: nil, start_project: project)
+    check_tree_entry_for_dir(branch_name, path)
 
-      Gitlab::Git::Blob.commit(raw_repository, options)
+    if start_branch_name
+      start_project.repository.
+        check_tree_entry_for_dir(start_branch_name, path)
     end
-  end
-
-  def update_file(user, path, content, branch:, previous_path:, message:, author_email: nil, author_name: nil)
-    update_branch_with_hooks(user, branch) do |ref|
-      options = {
-        commit: {
-          branch: ref,
-          message: message,
-          update_ref: false
-        },
-        file: {
-          content: content,
-          path: path,
-          update: true
-        }
-      }
-
-      options.merge!(get_committer_and_author(user, email: author_email, name: author_name))
 
-      if previous_path && previous_path != path
-        options[:file][:previous_path] = previous_path
-        Gitlab::Git::Blob.rename(raw_repository, options)
-      else
-        Gitlab::Git::Blob.commit(raw_repository, options)
+    commit_file(
+      user,
+      "#{path}/.gitkeep",
+      '',
+      message: message,
+      branch_name: branch_name,
+      update: false,
+      author_email: author_email,
+      author_name: author_name,
+      start_branch_name: start_branch_name,
+      start_project: start_project)
+  end
+  # rubocop:enable Metrics/ParameterLists
+
+  # rubocop:disable Metrics/ParameterLists
+  def commit_file(
+    user, path, content,
+    message:, branch_name:, update: true,
+    author_email: nil, author_name: nil,
+    start_branch_name: nil, start_project: project)
+    unless update
+      error_message = "Filename already exists; update not allowed"
+
+      if tree_entry_at(branch_name, path)
+        raise Gitlab::Git::Repository::InvalidBlobName.new(error_message)
       end
-    end
-  end
-
-  def remove_file(user, path, message, branch, author_email: nil, author_name: nil)
-    update_branch_with_hooks(user, branch) do |ref|
-      options = {
-        commit: {
-          branch: ref,
-          message: message,
-          update_ref: false
-        },
-        file: {
-          path: path
-        }
-      }
-
-      options.merge!(get_committer_and_author(user, email: author_email, name: author_name))
 
-      Gitlab::Git::Blob.remove(raw_repository, options)
+      if start_branch_name &&
+          start_project.repository.tree_entry_at(start_branch_name, path)
+        raise Gitlab::Git::Repository::InvalidBlobName.new(error_message)
+      end
     end
-  end
 
-  def multi_action(user:, branch:, message:, actions:, author_email: nil, author_name: nil)
-    update_branch_with_hooks(user, branch) do |ref|
+    multi_action(
+      user: user,
+      message: message,
+      branch_name: branch_name,
+      author_email: author_email,
+      author_name: author_name,
+      start_branch_name: start_branch_name,
+      start_project: start_project,
+      actions: [{ action: :create,
+                  file_path: path,
+                  content: content }])
+  end
+  # rubocop:enable Metrics/ParameterLists
+
+  # rubocop:disable Metrics/ParameterLists
+  def update_file(
+    user, path, content,
+    message:, branch_name:, previous_path:,
+    author_email: nil, author_name: nil,
+    start_branch_name: nil, start_project: project)
+    action = if previous_path && previous_path != path
+               :move
+             else
+               :update
+             end
+
+    multi_action(
+      user: user,
+      message: message,
+      branch_name: branch_name,
+      author_email: author_email,
+      author_name: author_name,
+      start_branch_name: start_branch_name,
+      start_project: start_project,
+      actions: [{ action: action,
+                  file_path: path,
+                  content: content,
+                  previous_path: previous_path }])
+  end
+  # rubocop:enable Metrics/ParameterLists
+
+  # rubocop:disable Metrics/ParameterLists
+  def remove_file(
+    user, path,
+    message:, branch_name:,
+    author_email: nil, author_name: nil,
+    start_branch_name: nil, start_project: project)
+    multi_action(
+      user: user,
+      message: message,
+      branch_name: branch_name,
+      author_email: author_email,
+      author_name: author_name,
+      start_branch_name: start_branch_name,
+      start_project: start_project,
+      actions: [{ action: :delete,
+                  file_path: path }])
+  end
+  # rubocop:enable Metrics/ParameterLists
+
+  # rubocop:disable Metrics/ParameterLists
+  def multi_action(
+    user:, branch_name:, message:, actions:,
+    author_email: nil, author_name: nil,
+    start_branch_name: nil, start_project: project)
+    GitOperationService.new(user, self).with_branch(
+      branch_name,
+      start_branch_name: start_branch_name,
+      start_project: start_project) do |start_commit|
       index = rugged.index
-      parents = []
-      branch = find_branch(ref)
 
-      if branch
-        last_commit = branch.dereferenced_target
-        index.read_tree(last_commit.raw_commit.tree)
-        parents = [last_commit.sha]
-      end
+      parents = if start_commit
+                  index.read_tree(start_commit.raw_commit.tree)
+                  [start_commit.sha]
+                else
+                  []
+                end
 
-      actions.each do |action|
-        case action[:action]
-        when :create, :update, :move
-          mode =
-            case action[:action]
-            when :update
-              index.get(action[:file_path])[:mode]
-            when :move
-              index.get(action[:previous_path])[:mode]
-            end
-          mode ||= 0o100644
-
-          index.remove(action[:previous_path]) if action[:action] == :move
-
-          content = action[:encoding] == 'base64' ? Base64.decode64(action[:content]) : action[:content]
-          oid = rugged.write(content, :blob)
-
-          index.add(path: action[:file_path], oid: oid, mode: mode)
-        when :delete
-          index.remove(action[:file_path])
-        end
+      actions.each do |act|
+        git_action(index, act)
       end
 
       options = {
@@ -906,6 +886,7 @@ class Repository
       Rugged::Commit.create(rugged, options)
     end
   end
+  # rubocop:enable Metrics/ParameterLists
 
   def get_committer_and_author(user, email: nil, name: nil)
     committer = user_to_committer(user)
@@ -918,7 +899,7 @@ class Repository
   end
 
   def user_to_committer(user)
-    Gitlab::Git::committer_hash(email: user.email, name: user.name)
+    Gitlab::Git.committer_hash(email: user.email, name: user.name)
   end
 
   def can_be_merged?(source_sha, target_branch)
@@ -933,16 +914,17 @@ class Repository
   end
 
   def merge(user, merge_request, options = {})
-    our_commit = rugged.branches[merge_request.target_branch].target
-    their_commit = rugged.lookup(merge_request.diff_head_sha)
+    GitOperationService.new(user, self).with_branch(
+      merge_request.target_branch) do |start_commit|
+      our_commit = start_commit.sha
+      their_commit = merge_request.diff_head_sha
 
-    raise "Invalid merge target" if our_commit.nil?
-    raise "Invalid merge source" if their_commit.nil?
+      raise 'Invalid merge target' unless our_commit
+      raise 'Invalid merge source' unless their_commit
 
-    merge_index = rugged.merge_commits(our_commit, their_commit)
-    return false if merge_index.conflicts?
+      merge_index = rugged.merge_commits(our_commit, their_commit)
+      break if merge_index.conflicts?
 
-    update_branch_with_hooks(user, merge_request.target_branch) do
       actual_options = options.merge(
         parents: [our_commit, their_commit],
         tree: merge_index.write_tree(rugged),
@@ -952,34 +934,48 @@ class Repository
       merge_request.update(in_progress_merge_commit_sha: commit_id)
       commit_id
     end
+  rescue Repository::CommitError # when merge_index.conflicts?
+    false
   end
 
-  def revert(user, commit, base_branch, revert_tree_id = nil)
-    source_sha = find_branch(base_branch).dereferenced_target.sha
-    revert_tree_id ||= check_revert_content(commit, base_branch)
+  def revert(
+    user, commit, branch_name, revert_tree_id = nil,
+    start_branch_name: nil, start_project: project)
+    revert_tree_id ||= check_revert_content(commit, branch_name)
 
     return false unless revert_tree_id
 
-    update_branch_with_hooks(user, base_branch) do
+    GitOperationService.new(user, self).with_branch(
+      branch_name,
+      start_branch_name: start_branch_name,
+      start_project: start_project) do |start_commit|
+
       committer = user_to_committer(user)
-      source_sha = Rugged::Commit.create(rugged,
+
+      Rugged::Commit.create(rugged,
         message: commit.revert_message(user),
         author: committer,
         committer: committer,
         tree: revert_tree_id,
-        parents: [rugged.lookup(source_sha)])
+        parents: [start_commit.sha])
     end
   end
 
-  def cherry_pick(user, commit, base_branch, cherry_pick_tree_id = nil)
-    source_sha = find_branch(base_branch).dereferenced_target.sha
-    cherry_pick_tree_id ||= check_cherry_pick_content(commit, base_branch)
+  def cherry_pick(
+    user, commit, branch_name, cherry_pick_tree_id = nil,
+    start_branch_name: nil, start_project: project)
+    cherry_pick_tree_id ||= check_cherry_pick_content(commit, branch_name)
 
     return false unless cherry_pick_tree_id
 
-    update_branch_with_hooks(user, base_branch) do
+    GitOperationService.new(user, self).with_branch(
+      branch_name,
+      start_branch_name: start_branch_name,
+      start_project: start_project) do |start_commit|
+
       committer = user_to_committer(user)
-      source_sha = Rugged::Commit.create(rugged,
+
+      Rugged::Commit.create(rugged,
         message: commit.message,
         author: {
           email: commit.author_email,
@@ -988,22 +984,22 @@ class Repository
         },
         committer: committer,
         tree: cherry_pick_tree_id,
-        parents: [rugged.lookup(source_sha)])
+        parents: [start_commit.sha])
     end
   end
 
-  def resolve_conflicts(user, branch, params)
-    update_branch_with_hooks(user, branch) do
+  def resolve_conflicts(user, branch_name, params)
+    GitOperationService.new(user, self).with_branch(branch_name) do
       committer = user_to_committer(user)
 
       Rugged::Commit.create(rugged, params.merge(author: committer, committer: committer))
     end
   end
 
-  def check_revert_content(commit, base_branch)
-    source_sha = find_branch(base_branch).dereferenced_target.sha
-    args       = [commit.id, source_sha]
-    args << { mainline: 1 } if commit.merge_commit?
+  def check_revert_content(target_commit, branch_name)
+    source_sha = commit(branch_name).sha
+    args       = [target_commit.sha, source_sha]
+    args << { mainline: 1 } if target_commit.merge_commit?
 
     revert_index = rugged.revert_commit(*args)
     return false if revert_index.conflicts?
@@ -1014,10 +1010,10 @@ class Repository
     tree_id
   end
 
-  def check_cherry_pick_content(commit, base_branch)
-    source_sha = find_branch(base_branch).dereferenced_target.sha
-    args       = [commit.id, source_sha]
-    args << 1 if commit.merge_commit?
+  def check_cherry_pick_content(target_commit, branch_name)
+    source_sha = commit(branch_name).sha
+    args       = [target_commit.sha, source_sha]
+    args << 1 if target_commit.merge_commit?
 
     cherry_pick_index = rugged.cherrypick_commit(*args)
     return false if cherry_pick_index.conflicts?
@@ -1075,6 +1071,28 @@ class Repository
     Gitlab::Popen.popen(args, path_to_repo).first.lines.map(&:strip)
   end
 
+  def with_repo_branch_commit(start_repository, start_branch_name)
+    branch_name_or_sha =
+      if start_repository == self
+        start_branch_name
+      else
+        tmp_ref = "refs/tmp/#{SecureRandom.hex}/head"
+
+        fetch_ref(
+          start_repository.path_to_repo,
+          "#{Gitlab::Git::BRANCH_REF_PREFIX}#{start_branch_name}",
+          tmp_ref
+        )
+
+        start_repository.commit(start_branch_name).sha
+      end
+
+    yield(commit(branch_name_or_sha))
+
+  ensure
+    rugged.references.delete(tmp_ref) if tmp_ref
+  end
+
   def fetch_ref(source_path, source_ref, target_ref)
     args = %W(#{Gitlab.config.git.bin_path} fetch --no-tags -f #{source_path} #{source_ref}:#{target_ref})
     Gitlab::Popen.popen(args, path_to_repo)
@@ -1084,39 +1102,6 @@ class Repository
     fetch_ref(path_to_repo, ref, ref_path)
   end
 
-  def update_branch_with_hooks(current_user, branch)
-    update_autocrlf_option
-
-    ref = Gitlab::Git::BRANCH_REF_PREFIX + branch
-    target_branch = find_branch(branch)
-    was_empty = empty?
-
-    # Make commit
-    newrev = yield(ref)
-
-    unless newrev
-      raise CommitError.new('Failed to create commit')
-    end
-
-    if rugged.lookup(newrev).parent_ids.empty? || target_branch.nil?
-      oldrev = Gitlab::Git::BLANK_SHA
-    else
-      oldrev = rugged.merge_base(newrev, target_branch.dereferenced_target.sha)
-    end
-
-    GitHooksService.new.execute(current_user, path_to_repo, oldrev, newrev, ref) do
-      update_ref!(ref, newrev, oldrev)
-
-      if was_empty || !target_branch
-        # If repo was empty expire cache
-        after_create if was_empty
-        after_create_branch
-      end
-    end
-
-    newrev
-  end
-
   def ls_files(ref)
     actual_ref = ref || root_ref
     raw_repository.ls_files(actual_ref)
@@ -1175,8 +1160,76 @@ class Repository
     end
   end
 
+  protected
+
+  def tree_entry_at(branch_name, path)
+    branch_exists?(branch_name) &&
+      # tree_entry is private
+      raw_repository.send(:tree_entry, commit(branch_name), path)
+  end
+
+  def check_tree_entry_for_dir(branch_name, path)
+    return unless branch_exists?(branch_name)
+
+    entry = tree_entry_at(branch_name, path)
+
+    return unless entry
+
+    if entry[:type] == :blob
+      raise Gitlab::Git::Repository::InvalidBlobName.new(
+        "Directory already exists as a file")
+    else
+      raise Gitlab::Git::Repository::InvalidBlobName.new(
+        "Directory already exists")
+    end
+  end
+
   private
 
+  def git_action(index, action)
+    path = normalize_path(action[:file_path])
+
+    if action[:action] == :move
+      previous_path = normalize_path(action[:previous_path])
+    end
+
+    case action[:action]
+    when :create, :update, :move
+      mode =
+        case action[:action]
+        when :update
+          index.get(path)[:mode]
+        when :move
+          index.get(previous_path)[:mode]
+        end
+      mode ||= 0o100644
+
+      index.remove(previous_path) if action[:action] == :move
+
+      content = if action[:encoding] == 'base64'
+                  Base64.decode64(action[:content])
+                else
+                  action[:content]
+                end
+
+      oid = rugged.write(content, :blob)
+
+      index.add(path: path, oid: oid, mode: mode)
+    when :delete
+      index.remove(path)
+    end
+  end
+
+  def normalize_path(path)
+    pathname = Gitlab::Git::PathHelper.normalize_path(path)
+
+    if pathname.each_filename.include?('..')
+      raise Gitlab::Git::Repository::InvalidBlobName.new('Invalid path')
+    end
+
+    pathname.to_s
+  end
+
   def refs_directory_exists?
     return false unless path_with_namespace
 
diff --git a/app/services/commits/change_service.rb b/app/services/commits/change_service.rb
index 4d410f66c55..25e22f14e60 100644
--- a/app/services/commits/change_service.rb
+++ b/app/services/commits/change_service.rb
@@ -4,7 +4,8 @@ module Commits
     class ChangeError < StandardError; end
 
     def execute
-      @source_project = params[:source_project] || @project
+      @start_project = params[:start_project] || @project
+      @start_branch = params[:start_branch]
       @target_branch = params[:target_branch]
       @commit = params[:commit]
       @create_merge_request = params[:create_merge_request].present?
@@ -25,13 +26,28 @@ module Commits
     def commit_change(action)
       raise NotImplementedError unless repository.respond_to?(action)
 
-      into = @create_merge_request ? @commit.public_send("#{action}_branch_name") : @target_branch
-      tree_id = repository.public_send("check_#{action}_content", @commit, @target_branch)
+      if @create_merge_request
+        into = @commit.public_send("#{action}_branch_name")
+        tree_branch = @start_branch
+      else
+        into = tree_branch = @target_branch
+      end
+
+      tree_id = repository.public_send(
+        "check_#{action}_content", @commit, tree_branch)
 
       if tree_id
-        create_target_branch(into) if @create_merge_request
+        validate_target_branch(into) if @create_merge_request
+
+        repository.public_send(
+          action,
+          current_user,
+          @commit,
+          into,
+          tree_id,
+          start_project: @start_project,
+          start_branch_name: @start_branch)
 
-        repository.public_send(action, current_user, @commit, into, tree_id)
         success
       else
         error_msg = "Sorry, we cannot #{action.to_s.dasherize} this #{@commit.change_type_title(current_user)} automatically.
@@ -50,12 +66,12 @@ module Commits
       true
     end
 
-    def create_target_branch(new_branch)
+    def validate_target_branch(new_branch)
       # Temporary branch exists and contains the change commit
-      return success if repository.find_branch(new_branch)
+      return if repository.find_branch(new_branch)
 
-      result = CreateBranchService.new(@project, current_user)
-                                  .execute(new_branch, @target_branch, source_project: @source_project)
+      result = ValidateNewBranchService.new(@project, current_user)
+        .execute(new_branch)
 
       if result[:status] == :error
         raise ChangeError, "There was an error creating the source branch: #{result[:message]}"
diff --git a/app/services/compare_service.rb b/app/services/compare_service.rb
index 5e8fafca98c..ab4c02a97a0 100644
--- a/app/services/compare_service.rb
+++ b/app/services/compare_service.rb
@@ -3,23 +3,27 @@ require 'securerandom'
 # Compare 2 branches for one repo or between repositories
 # and return Gitlab::Git::Compare object that responds to commits and diffs
 class CompareService
-  def execute(source_project, source_branch, target_project, target_branch, straight: false)
-    source_commit = source_project.commit(source_branch)
-    return unless source_commit
+  attr_reader :start_project, :start_branch_name
 
-    source_sha = source_commit.sha
+  def initialize(new_start_project, new_start_branch_name)
+    @start_project = new_start_project
+    @start_branch_name = new_start_branch_name
+  end
 
+  def execute(target_project, target_branch, straight: false)
     # If compare with other project we need to fetch ref first
-    unless target_project == source_project
-      random_string = SecureRandom.hex
+    target_project.repository.with_repo_branch_commit(
+      start_project.repository,
+      start_branch_name) do |commit|
+      break unless commit
 
-      target_project.repository.fetch_ref(
-        source_project.repository.path_to_repo,
-        "refs/heads/#{source_branch}",
-        "refs/tmp/#{random_string}/head"
-      )
+      compare(commit.sha, target_project, target_branch, straight)
     end
+  end
+
+  private
 
+  def compare(source_sha, target_project, target_branch, straight)
     raw_compare = Gitlab::Git::Compare.new(
       target_project.repository.raw_repository,
       target_branch,
diff --git a/app/services/create_branch_service.rb b/app/services/create_branch_service.rb
index e004a303496..77459d8779d 100644
--- a/app/services/create_branch_service.rb
+++ b/app/services/create_branch_service.rb
@@ -1,31 +1,11 @@
 class CreateBranchService < BaseService
-  def execute(branch_name, ref, source_project: @project)
-    valid_branch = Gitlab::GitRefValidator.validate(branch_name)
+  def execute(branch_name, ref)
+    result = ValidateNewBranchService.new(project, current_user)
+      .execute(branch_name)
 
-    unless valid_branch
-      return error('Branch name is invalid')
-    end
-
-    repository = project.repository
-    existing_branch = repository.find_branch(branch_name)
-
-    if existing_branch
-      return error('Branch already exists')
-    end
-
-    new_branch = if source_project != @project
-                   repository.fetch_ref(
-                     source_project.repository.path_to_repo,
-                     "refs/heads/#{ref}",
-                     "refs/heads/#{branch_name}"
-                   )
-
-                   repository.after_create_branch
+    return result if result[:status] == :error
 
-                   repository.find_branch(branch_name)
-                 else
-                   repository.add_branch(current_user, branch_name, ref)
-                 end
+    new_branch = repository.add_branch(current_user, branch_name, ref)
 
     if new_branch
       success(new_branch)
diff --git a/app/services/delete_tag_service.rb b/app/services/delete_tag_service.rb
index a44dee14a0f..9d4bffb93e9 100644
--- a/app/services/delete_tag_service.rb
+++ b/app/services/delete_tag_service.rb
@@ -7,7 +7,7 @@ class DeleteTagService < BaseService
       return error('No such tag', 404)
     end
 
-    if repository.rm_tag(tag_name)
+    if repository.rm_tag(current_user, tag_name)
       release = project.releases.find_by(tag: tag_name)
       release.destroy if release
 
diff --git a/app/services/files/base_service.rb b/app/services/files/base_service.rb
index 9bd4bd464f7..0a25f56d24c 100644
--- a/app/services/files/base_service.rb
+++ b/app/services/files/base_service.rb
@@ -3,9 +3,9 @@ module Files
     class ValidationError < StandardError; end
 
     def execute
-      @source_project = params[:source_project] || @project
-      @source_branch = params[:source_branch]
-      @target_branch  = params[:target_branch]
+      @start_project = params[:start_project] || @project
+      @start_branch = params[:start_branch]
+      @target_branch = params[:target_branch]
 
       @commit_message = params[:commit_message]
       @file_path      = params[:file_path]
@@ -22,10 +22,8 @@ module Files
       # Validate parameters
       validate
 
-      # Create new branch if it different from source_branch
-      if different_branch?
-        create_target_branch
-      end
+      # Create new branch if it different from start_branch
+      validate_target_branch if different_branch?
 
       result = commit
       if result
@@ -40,7 +38,7 @@ module Files
     private
 
     def different_branch?
-      @source_branch != @target_branch || @source_project != @project
+      @start_branch != @target_branch || @start_project != @project
     end
 
     def file_has_changed?
@@ -61,22 +59,23 @@ module Files
       end
 
       unless project.empty_repo?
-        unless @source_project.repository.branch_names.include?(@source_branch)
+        unless @start_project.repository.branch_exists?(@start_branch)
           raise_error('You can only create or edit files when you are on a branch')
         end
 
         if different_branch?
-          if repository.branch_names.include?(@target_branch)
+          if repository.branch_exists?(@target_branch)
             raise_error('Branch with such name already exists. You need to switch to this branch in order to make changes')
           end
         end
       end
     end
 
-    def create_target_branch
-      result = CreateBranchService.new(project, current_user).execute(@target_branch, @source_branch, source_project: @source_project)
+    def validate_target_branch
+      result = ValidateNewBranchService.new(project, current_user).
+        execute(@target_branch)
 
-      unless result[:status] == :success
+      if result[:status] == :error
         raise_error("Something went wrong when we tried to create #{@target_branch} for you: #{result[:message]}")
       end
     end
diff --git a/app/services/files/create_dir_service.rb b/app/services/files/create_dir_service.rb
index e5b4d60e467..858de5f0538 100644
--- a/app/services/files/create_dir_service.rb
+++ b/app/services/files/create_dir_service.rb
@@ -1,7 +1,15 @@
 module Files
   class CreateDirService < Files::BaseService
     def commit
-      repository.commit_dir(current_user, @file_path, @commit_message, @target_branch, author_email: @author_email, author_name: @author_name)
+      repository.commit_dir(
+        current_user,
+        @file_path,
+        message: @commit_message,
+        branch_name: @target_branch,
+        author_email: @author_email,
+        author_name: @author_name,
+        start_project: @start_project,
+        start_branch_name: @start_branch)
     end
 
     def validate
diff --git a/app/services/files/create_service.rb b/app/services/files/create_service.rb
index b23576b9a28..88dd7bbaedb 100644
--- a/app/services/files/create_service.rb
+++ b/app/services/files/create_service.rb
@@ -1,7 +1,17 @@
 module Files
   class CreateService < Files::BaseService
     def commit
-      repository.commit_file(current_user, @file_path, @file_content, @commit_message, @target_branch, false, author_email: @author_email, author_name: @author_name)
+      repository.commit_file(
+        current_user,
+        @file_path,
+        @file_content,
+        message: @commit_message,
+        branch_name: @target_branch,
+        update: false,
+        author_email: @author_email,
+        author_name: @author_name,
+        start_project: @start_project,
+        start_branch_name: @start_branch)
     end
 
     def validate
@@ -24,7 +34,7 @@ module Files
       unless project.empty_repo?
         @file_path.slice!(0) if @file_path.start_with?('/')
 
-        blob = repository.blob_at_branch(@source_branch, @file_path)
+        blob = repository.blob_at_branch(@start_branch, @file_path)
 
         if blob
           raise_error('Your changes could not be committed because a file with the same name already exists')
diff --git a/app/services/files/delete_service.rb b/app/services/files/delete_service.rb
index 4f7e7a5baaa..50f0ffcac9f 100644
--- a/app/services/files/delete_service.rb
+++ b/app/services/files/delete_service.rb
@@ -1,7 +1,15 @@
 module Files
   class DeleteService < Files::BaseService
     def commit
-      repository.remove_file(current_user, @file_path, @commit_message, @target_branch, author_email: @author_email, author_name: @author_name)
+      repository.remove_file(
+        current_user,
+        @file_path,
+        message: @commit_message,
+        branch_name: @target_branch,
+        author_email: @author_email,
+        author_name: @author_name,
+        start_project: @start_project,
+        start_branch_name: @start_branch)
     end
   end
 end
diff --git a/app/services/files/multi_service.rb b/app/services/files/multi_service.rb
index 54446e90007..6ba868df04d 100644
--- a/app/services/files/multi_service.rb
+++ b/app/services/files/multi_service.rb
@@ -5,11 +5,13 @@ module Files
     def commit
       repository.multi_action(
         user: current_user,
-        branch: @target_branch,
         message: @commit_message,
+        branch_name: @target_branch,
         actions: params[:actions],
         author_email: @author_email,
-        author_name: @author_name
+        author_name: @author_name,
+        start_project: @start_project,
+        start_branch_name: @start_branch
       )
     end
 
@@ -61,7 +63,7 @@ module Files
     end
 
     def last_commit
-      Gitlab::Git::Commit.last_for_path(repository, @source_branch, @file_path)
+      Gitlab::Git::Commit.last_for_path(repository, @start_branch, @file_path)
     end
 
     def regex_check(file)
diff --git a/app/services/files/update_service.rb b/app/services/files/update_service.rb
index 47a18e3e132..a71fe61a4b6 100644
--- a/app/services/files/update_service.rb
+++ b/app/services/files/update_service.rb
@@ -4,11 +4,13 @@ module Files
 
     def commit
       repository.update_file(current_user, @file_path, @file_content,
-                             branch: @target_branch,
-                             previous_path: @previous_path,
                              message: @commit_message,
+                             branch_name: @target_branch,
+                             previous_path: @previous_path,
                              author_email: @author_email,
-                             author_name: @author_name)
+                             author_name: @author_name,
+                             start_project: @start_project,
+                             start_branch_name: @start_branch)
     end
 
     private
@@ -23,7 +25,7 @@ module Files
 
     def last_commit
       @last_commit ||= Gitlab::Git::Commit.
-        last_for_path(@source_project.repository, @source_branch, @file_path)
+        last_for_path(@start_project.repository, @start_branch, @file_path)
     end
   end
 end
diff --git a/app/services/git_hooks_service.rb b/app/services/git_hooks_service.rb
index 6cd3908d43a..d222d1e63aa 100644
--- a/app/services/git_hooks_service.rb
+++ b/app/services/git_hooks_service.rb
@@ -18,9 +18,9 @@ class GitHooksService
       end
     end
 
-    yield self
-
-    run_hook('post-receive')
+    yield(self).tap do
+      run_hook('post-receive')
+    end
   end
 
   private
diff --git a/app/services/git_operation_service.rb b/app/services/git_operation_service.rb
new file mode 100644
index 00000000000..27bcc047601
--- /dev/null
+++ b/app/services/git_operation_service.rb
@@ -0,0 +1,179 @@
+class GitOperationService
+  attr_reader :user, :repository
+
+  def initialize(new_user, new_repository)
+    @user = new_user
+    @repository = new_repository
+  end
+
+  def add_branch(branch_name, newrev)
+    ref = Gitlab::Git::BRANCH_REF_PREFIX + branch_name
+    oldrev = Gitlab::Git::BLANK_SHA
+
+    update_ref_in_hooks(ref, newrev, oldrev)
+  end
+
+  def rm_branch(branch)
+    ref = Gitlab::Git::BRANCH_REF_PREFIX + branch.name
+    oldrev = branch.target
+    newrev = Gitlab::Git::BLANK_SHA
+
+    update_ref_in_hooks(ref, newrev, oldrev)
+  end
+
+  def add_tag(tag_name, newrev, options = {})
+    ref = Gitlab::Git::TAG_REF_PREFIX + tag_name
+    oldrev = Gitlab::Git::BLANK_SHA
+
+    with_hooks(ref, newrev, oldrev) do |service|
+      # We want to pass the OID of the tag object to the hooks. For an
+      # annotated tag we don't know that OID until after the tag object
+      # (raw_tag) is created in the repository. That is why we have to
+      # update the value after creating the tag object. Only the
+      # "post-receive" hook will receive the correct value in this case.
+      raw_tag = repository.rugged.tags.create(tag_name, newrev, options)
+      service.newrev = raw_tag.target_id
+    end
+  end
+
+  def rm_tag(tag)
+    ref = Gitlab::Git::TAG_REF_PREFIX + tag.name
+    oldrev = tag.target
+    newrev = Gitlab::Git::BLANK_SHA
+
+    update_ref_in_hooks(ref, newrev, oldrev) do
+      repository.rugged.tags.delete(tag_name)
+    end
+  end
+
+  # Whenever `start_branch_name` is passed, if `branch_name` doesn't exist,
+  # it would be created from `start_branch_name`.
+  # If `start_project` is passed, and the branch doesn't exist,
+  # it would try to find the commits from it instead of current repository.
+  def with_branch(
+    branch_name,
+    start_branch_name: nil,
+    start_project: repository.project,
+    &block)
+
+    check_with_branch_arguments!(
+      branch_name, start_branch_name, start_project)
+
+    update_branch_with_hooks(branch_name) do
+      repository.with_repo_branch_commit(
+        start_project.repository,
+        start_branch_name || branch_name,
+        &block)
+    end
+  end
+
+  private
+
+  def update_branch_with_hooks(branch_name)
+    update_autocrlf_option
+
+    was_empty = repository.empty?
+
+    # Make commit
+    newrev = yield
+
+    unless newrev
+      raise Repository::CommitError.new('Failed to create commit')
+    end
+
+    branch = repository.find_branch(branch_name)
+    oldrev = find_oldrev_from_branch(newrev, branch)
+
+    ref = Gitlab::Git::BRANCH_REF_PREFIX + branch_name
+    update_ref_in_hooks(ref, newrev, oldrev)
+
+    # If repo was empty expire cache
+    repository.after_create if was_empty
+    repository.after_create_branch if
+      was_empty || Gitlab::Git.blank_ref?(oldrev)
+
+    newrev
+  end
+
+  def find_oldrev_from_branch(newrev, branch)
+    return Gitlab::Git::BLANK_SHA unless branch
+
+    oldrev = branch.target
+
+    if oldrev == repository.rugged.merge_base(newrev, branch.target)
+      oldrev
+    else
+      raise Repository::CommitError.new('Branch diverged')
+    end
+  end
+
+  def update_ref_in_hooks(ref, newrev, oldrev)
+    with_hooks(ref, newrev, oldrev) do
+      update_ref(ref, newrev, oldrev)
+    end
+  end
+
+  def with_hooks(ref, newrev, oldrev)
+    GitHooksService.new.execute(
+      user,
+      repository.path_to_repo,
+      oldrev,
+      newrev,
+      ref) do |service|
+
+      yield(service)
+    end
+  end
+
+  def update_ref(ref, newrev, oldrev)
+    # We use 'git update-ref' because libgit2/rugged currently does not
+    # offer 'compare and swap' ref updates. Without compare-and-swap we can
+    # (and have!) accidentally reset the ref to an earlier state, clobbering
+    # commits. See also https://github.com/libgit2/libgit2/issues/1534.
+    command = %W[#{Gitlab.config.git.bin_path} update-ref --stdin -z]
+    _, status = Gitlab::Popen.popen(
+      command,
+      repository.path_to_repo) do |stdin|
+      stdin.write("update #{ref}\x00#{newrev}\x00#{oldrev}\x00")
+    end
+
+    unless status.zero?
+      raise Repository::CommitError.new(
+        "Could not update branch #{Gitlab::Git.branch_name(ref)}." \
+        " Please refresh and try again.")
+    end
+  end
+
+  def update_autocrlf_option
+    if repository.raw_repository.autocrlf != :input
+      repository.raw_repository.autocrlf = :input
+    end
+  end
+
+  def check_with_branch_arguments!(
+    branch_name, start_branch_name, start_project)
+    return if repository.branch_exists?(branch_name)
+
+    if repository.project != start_project
+      unless start_branch_name
+        raise ArgumentError,
+          'Should also pass :start_branch_name if' +
+          ' :start_project is different from current project'
+      end
+
+      unless start_project.repository.branch_exists?(start_branch_name)
+        raise ArgumentError,
+          "Cannot find branch #{branch_name} nor" \
+          " #{start_branch_name} from" \
+          " #{start_project.path_with_namespace}"
+      end
+    elsif start_branch_name
+      unless repository.branch_exists?(start_branch_name)
+        raise ArgumentError,
+          "Cannot find branch #{branch_name} nor" \
+          " #{start_branch_name} from" \
+          " #{repository.project.path_with_namespace}"
+      end
+    end
+  end
+end
diff --git a/app/services/merge_requests/build_service.rb b/app/services/merge_requests/build_service.rb
index 1d6d2754559..f4d52e3ebbd 100644
--- a/app/services/merge_requests/build_service.rb
+++ b/app/services/merge_requests/build_service.rb
@@ -47,9 +47,10 @@ module MergeRequests
     end
 
     def compare_branches
-      compare = CompareService.new.execute(
+      compare = CompareService.new(
         source_project,
-        source_branch,
+        source_branch
+      ).execute(
         target_project,
         target_branch
       )
diff --git a/app/services/validate_new_branch_service.rb b/app/services/validate_new_branch_service.rb
new file mode 100644
index 00000000000..2f61be184ce
--- /dev/null
+++ b/app/services/validate_new_branch_service.rb
@@ -0,0 +1,22 @@
+require_relative 'base_service'
+
+class ValidateNewBranchService < BaseService
+  def execute(branch_name)
+    valid_branch = Gitlab::GitRefValidator.validate(branch_name)
+
+    unless valid_branch
+      return error('Branch name is invalid')
+    end
+
+    repository = project.repository
+    existing_branch = repository.find_branch(branch_name)
+
+    if existing_branch
+      return error('Branch already exists')
+    end
+
+    success
+  rescue GitHooksService::PreReceiveError => ex
+    error(ex.message)
+  end
+end
diff --git a/app/workers/emails_on_push_worker.rb b/app/workers/emails_on_push_worker.rb
index b9cd49985dc..f5ccc84c160 100644
--- a/app/workers/emails_on_push_worker.rb
+++ b/app/workers/emails_on_push_worker.rb
@@ -33,13 +33,15 @@ class EmailsOnPushWorker
     reverse_compare = false
 
     if action == :push
-      compare = CompareService.new.execute(project, after_sha, project, before_sha)
+      compare = CompareService.new(project, after_sha)
+        .execute(project, before_sha)
       diff_refs = compare.diff_refs
 
       return false if compare.same
 
       if compare.commits.empty?
-        compare = CompareService.new.execute(project, before_sha, project, after_sha)
+        compare = CompareService.new(project, before_sha)
+          .execute(project, after_sha)
         diff_refs = compare.diff_refs
 
         reverse_compare = true