Add 'squash and rebase' feature to CE

app/assets/javascripts/vue_merge_request_widget/components/states/mr_widget_squash_before_merge.vue

-/*
-The squash-before-merge button is EE only, but it's located right in the middle
-of the readyToMerge state component template.
-
-If we didn't declare this component in CE, we'd need to maintain a separate copy
-of the readyToMergeState template in EE, which is pretty big and likely to change.
-
-Instead, in CE, we declare the component, but it's hidden and is configured to do nothing.
-In EE, the configuration extends this object to add a functioning squash-before-merge
-button.
-*/
-
 <script>
-  export default {};
+import Icon from '~/vue_shared/components/icon.vue';
+import eventHub from '~/vue_merge_request_widget/event_hub';
+import tooltip from '~/vue_shared/directives/tooltip';
+
+export default {
+  components: {
+    Icon,
+  },
+  directives: {
+    tooltip,
+  },
+  props: {
+    mr: {
+      type: Object,
+      required: true,
+    },
+    isMergeButtonDisabled: {
+      type: Boolean,
+      required: true,
+    },
+  },
+  data() {
+    return {
+      squashBeforeMerge: this.mr.squash,
+    };
+  },
+  methods: {
+    updateSquashModel() {
+      eventHub.$emit('MRWidgetUpdateSquash', this.squashBeforeMerge);
+    },
+  },
+};
 </script>
+
+<template>
+  <div class="accept-control inline">
+    <label class="merge-param-checkbox">
+      <input
+        type="checkbox"
+        name="squash"
+        class="qa-squash-checkbox"
+        :disabled="isMergeButtonDisabled"
+        v-model="squashBeforeMerge"
+        @change="updateSquashModel"
+      />
+      {{ __('Squash commits') }}
+    </label>
+    <a
+      :href="mr.squashBeforeMergeHelpPath"
+      data-title="About this feature"
+      data-placement="bottom"
+      target="_blank"
+      rel="noopener noreferrer nofollow"
+      data-container="body"
+      v-tooltip
+    >
+      <icon
+        name="question-o"
+      />
+    </a>
+  </div>
+</template>

app/assets/javascripts/vue_merge_request_widget/components/states/ready_to_merge.vue

@@ -6,11 +6,13 @@ import MergeRequest from '../../../merge_request';
 import Flash from '../../../flash';
 import statusIcon from '../mr_widget_status_icon.vue';
 import eventHub from '../../event_hub';
+import SquashBeforeMerge from './mr_widget_squash_before_merge.vue';
 
 export default {
   name: 'ReadyToMerge',
   components: {
     statusIcon,
+    'squash-before-merge': SquashBeforeMerge,
   },
   props: {
     mr: { type: Object, required: true },
@@ -101,6 +103,12 @@ export default {
       return enableSquashBeforeMerge && commitsCount > 1;
     },
   },
+  created() {
+    eventHub.$on('MRWidgetUpdateSquash', this.handleUpdateSquash);
+  },
+  beforeDestroy() {
+    eventHub.$off('MRWidgetUpdateSquash', this.handleUpdateSquash);
+  },
   methods: {
     shouldShowMergeControls() {
       return this.mr.isMergeAllowed || this.shouldShowMergeWhenPipelineSucceedsText;
@@ -128,13 +136,9 @@ export default {
         commit_message: this.commitMessage,
         merge_when_pipeline_succeeds: this.setToMergeWhenPipelineSucceeds,
         should_remove_source_branch: this.removeSourceBranch === true,
+        squash: this.mr.squash,
       };
 
-      // Only truthy in EE extension of this component
-      if (this.setAdditionalParams) {
-        this.setAdditionalParams(options);
-      }
-
       this.isMakingRequest = true;
       this.service.merge(options)
         .then(res => res.data)
@@ -154,6 +158,9 @@ export default {
           new Flash('Something went wrong. Please try again.'); // eslint-disable-line
         });
     },
+    handleUpdateSquash(val) {
+      this.mr.squash = val;
+    },
     initiateMergePolling() {
       simplePoll((continuePolling, stopPolling) => {
         this.handleMergePolling(continuePolling, stopPolling);

app/assets/javascripts/vue_merge_request_widget/stores/mr_widget_store.js

@@ -15,6 +15,11 @@ export default class MergeRequestStore {
     const currentUser = data.current_user;
     const pipelineStatus = data.pipeline ? data.pipeline.details.status : null;
 
+    this.squash = data.squash;
+    this.squashBeforeMergeHelpPath = this.squashBeforeMergeHelpPath ||
+      data.squash_before_merge_help_path;
+    this.enableSquashBeforeMerge = this.enableSquashBeforeMerge || true;
+
     this.title = data.title;
     this.targetBranch = data.target_branch;
     this.sourceBranch = data.source_branch;

app/controllers/projects/merge_requests/application_controller.rb

@@ -24,6 +24,7 @@ def merge_request_params_attributes
       :source_branch,
       :source_project_id,
       :state_event,
+      :squash,
       :target_branch,
       :target_project_id,
       :task_num,

app/controllers/projects/merge_requests_controller.rb

@@ -253,7 +253,7 @@ def merge_params
   end
 
   def merge_params_attributes
-    [:should_remove_source_branch, :commit_message]
+    [:should_remove_source_branch, :commit_message, :squash]
   end
 
   def merge_when_pipeline_succeeds_active?
@@ -282,7 +282,7 @@ def merge!
 
     return :sha_mismatch if params[:sha] != @merge_request.diff_head_sha
 
-    @merge_request.update(merge_error: nil)
+    @merge_request.update(merge_error: nil, squash: merge_params.fetch(:squash, false))
 
     if params[:merge_when_pipeline_succeeds].present?
       return :failed unless @merge_request.actual_head_pipeline

app/helpers/merge_requests_helper.rb

@@ -97,8 +97,9 @@ def merge_params(merge_request)
     {
       merge_when_pipeline_succeeds: true,
       should_remove_source_branch: true,
-      sha: merge_request.diff_head_sha
-    }.merge(merge_params_ee(merge_request))
+      sha: merge_request.diff_head_sha,
+      squash: merge_request.squash
+    }
   end
 
   def tab_link_for(merge_request, tab, options = {}, &block)
@@ -149,8 +150,4 @@ def merge_request_source_project_for_project(project = @project)
       current_user.fork_of(project)
     end
   end
-
-  def merge_params_ee(merge_request)
-    {}
-  end
 end

app/models/merge_request.rb

@@ -1140,4 +1140,11 @@ def can_allow_maintainer_to_push?(user)
     maintainer_push_possible? &&
       Ability.allowed?(user, :push_code, source_project)
   end
+
+  def squash_in_progress?
+    # The source project can be deleted
+    return false unless source_project
+
+    source_project.repository.squash_in_progress?(id)
+  end
 end

app/models/repository.rb

@@ -957,6 +957,14 @@ def rebase(user, merge_request)
                                        remote_branch: merge_request.target_branch)
   end
 
+  def squash(user, merge_request)
+    raw.squash(user, merge_request.id, branch: merge_request.target_branch,
+                                       start_sha: merge_request.diff_start_sha,
+                                       end_sha: merge_request.diff_head_sha,
+                                       author: merge_request.author,
+                                       message: merge_request.title)
+  end
+
   private
 
   # TODO Generice finder, later split this on finders by Ref or Oid

app/serializers/merge_request_widget_entity.rb

@@ -10,6 +10,7 @@ class MergeRequestWidgetEntity < IssuableEntity
   expose :merge_when_pipeline_succeeds
   expose :source_branch
   expose :source_project_id
+  expose :squash
   expose :target_branch
   expose :target_project_id
   expose :allow_maintainer_to_push

app/services/merge_requests/merge_service.rb

@@ -34,6 +34,19 @@ def execute(merge_request)
       handle_merge_error(log_message: e.message, save_message_on_model: true)
     end
 
+    def source
+      return merge_request.diff_head_sha unless merge_request.squash
+
+      squash_result = ::MergeRequests::SquashService.new(project, current_user, params).execute(merge_request)
+
+      case squash_result[:status]
+      when :success
+        squash_result[:squash_sha]
+      when :error
+        raise ::MergeRequests::MergeService::MergeError, squash_result[:message]
+      end
+    end
+
     private
 
     def error_check!
@@ -116,9 +129,5 @@ def log_info(message)
     def merge_request_info
       merge_request.to_reference(full: true)
     end
-
-    def source
-      @source ||= @merge_request.diff_head_sha
-    end
   end
 end

app/services/merge_requests/squash_service.rb

+module MergeRequests
+  class SquashService < MergeRequests::WorkingCopyBaseService
+    def execute(merge_request)
+      @merge_request = merge_request
+      @repository = target_project.repository
+
+      squash || error('Failed to squash. Should be done manually.')
+    end
+
+    def squash
+      if merge_request.commits_count < 2
+        return success(squash_sha: merge_request.diff_head_sha)
+      end
+
+      if merge_request.squash_in_progress?
+        return error('Squash task canceled: another squash is already in progress.')
+      end
+
+      squash_sha = repository.squash(current_user, merge_request)
+
+      success(squash_sha: squash_sha)
+    rescue => e
+      log_error("Failed to squash merge request #{merge_request.to_reference(full: true)}:")
+      log_error(e.message)
+      false
+    end
+  end
+end

app/views/projects/merge_requests/show.html.haml

@@ -20,6 +20,8 @@
       window.gl = window.gl || {};
       window.gl.mrWidgetData = #{serialize_issuable(@merge_request, serializer: 'widget')}
 
+      window.gl.mrWidgetData.squash_before_merge_help_path = '#{help_page_path("user/project/merge_requests/squash_and_merge")}';
+
     #js-vue-mr-widget.mr-widget
 
     .content-block.content-block-small.emoji-list-container.js-noteable-awards

app/views/shared/issuable/form/_merge_params.html.haml

@@ -15,3 +15,12 @@
           = hidden_field_tag 'merge_request[force_remove_source_branch]', '0', id: nil
           = check_box_tag 'merge_request[force_remove_source_branch]', '1', issuable.force_remove_source_branch?
           Remove source branch when merge request is accepted.
+
+.form-group
+  .col-sm-10.col-sm-offset-2
+    .checkbox
+      = label_tag 'merge_request[squash]' do
+        = hidden_field_tag 'merge_request[squash]', '0', id: nil
+        = check_box_tag 'merge_request[squash]', '1', issuable.squash
+        Squash commits when merge request is accepted.
+        = link_to 'About this feature', help_page_path('user/project/merge_requests/squash_and_merge')

changelogs/unreleased/blackst0ne-squash-and-merge-in-gitlab-core-ce.yml

+---
+title: Add `Squash and merge` to GitLab Core (CE)
+merge_request: 18956
+author: "@blackst0ne"
+type: added

db/migrate/20180515005612_add_squash_to_merge_requests.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddSquashToMergeRequests < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+  disable_ddl_transaction!
+
+  DOWNTIME = false
+
+  def up
+    unless column_exists?(:merge_requests, :squash)
+      add_column_with_default :merge_requests, :squash, :boolean, default: false, allow_null: false
+    end
+  end
+
+  def down
+    remove_column :merge_requests, :squash if column_exists?(:merge_requests, :squash)
+  end
+end

db/schema.rb

@@ -1217,6 +1217,7 @@
     t.integer "latest_merge_request_diff_id"
     t.string "rebase_commit_sha"
     t.boolean "allow_maintainer_to_push"
+    t.boolean "squash", default: false, null: false
   end
 
   add_index "merge_requests", ["assignee_id"], name: "index_merge_requests_on_assignee_id", using: :btree

doc/api/merge_requests.md

@@ -107,6 +107,7 @@ Parameters:
     "changes_count": "1",
     "should_remove_source_branch": true,
     "force_remove_source_branch": false,
+    "squash": false,
     "web_url": "http://example.com/example/example/merge_requests/1",
     "time_stats": {
       "time_estimate": 0,
@@ -226,6 +227,7 @@ Parameters:
     "changes_count": "1",
     "should_remove_source_branch": true,
     "force_remove_source_branch": false,
+    "squash": false,
     "web_url": "http://example.com/example/example/merge_requests/1",
     "discussion_locked": false,
     "time_stats": {
@@ -305,6 +307,7 @@ Parameters:
   "changes_count": "1",
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
+  "squash": false,
   "web_url": "http://example.com/example/example/merge_requests/1",
   "discussion_locked": false,
   "time_stats": {
@@ -541,7 +544,8 @@ POST /projects/:id/merge_requests
 | `labels`                   | string  | no       | Labels for MR as a comma-separated list                                         |
 | `milestone_id`             | integer | no       | The global ID of a milestone                                                           |
 | `remove_source_branch`     | boolean | no       | Flag indicating if a merge request should remove the source branch when merging |
-| `allow_maintainer_to_push` | boolean | no       | Whether or not a maintainer of the target project can push to the source branch  |
+| `allow_maintainer_to_push` | boolean | no       | Whether or not a maintainer of the target project can push to the source branch |
+| `squash`                   | boolean | no       | Squash commits into a single commit when merging                                |
 
 ```json
 {
@@ -595,6 +599,7 @@ POST /projects/:id/merge_requests
   "changes_count": "1",
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
+  "squash": false,
   "web_url": "http://example.com/example/example/merge_requests/1",
   "discussion_locked": false,
   "allow_maintainer_to_push": false,
@@ -627,6 +632,7 @@ PUT /projects/:id/merge_requests/:merge_request_iid
 | `description`              | string  | no       | Description of MR                                                               |
 | `state_event`              | string  | no       | New state (close/reopen)                                                        |
 | `remove_source_branch`     | boolean | no       | Flag indicating if a merge request should remove the source branch when merging |
+| `squash`                   | boolean | no       | Squash commits into a single commit when merging |
 | `discussion_locked`        | boolean | no       | Flag indicating if the merge request's discussion is locked. If the discussion is locked only project members can add, edit or resolve comments. |
 | `allow_maintainer_to_push` | boolean | no       | Whether or not a maintainer of the target project can push to the source branch |
 
@@ -683,6 +689,7 @@ Must include at least one non-required attribute from above.
   "changes_count": "1",
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
+  "squash": false,
   "web_url": "http://example.com/example/example/merge_requests/1",
   "discussion_locked": false,
   "allow_maintainer_to_push": false,
@@ -790,6 +797,7 @@ Parameters:
   "changes_count": "1",
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
+  "squash": false,
   "web_url": "http://example.com/example/example/merge_requests/1",
   "discussion_locked": false,
   "time_stats": {
@@ -868,6 +876,7 @@ Parameters:
   "changes_count": "1",
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
+  "squash": false,
   "web_url": "http://example.com/example/example/merge_requests/1",
   "discussion_locked": false,
   "time_stats": {
@@ -1200,6 +1209,7 @@ Example response:
     "changes_count": "1",
     "should_remove_source_branch": true,
     "force_remove_source_branch": false,
+    "squash": false,
     "web_url": "http://example.com/example/example/merge_requests/1"
   },
   "target_url": "https://gitlab.example.com/gitlab-org/gitlab-ci/merge_requests/7",

doc/user/project/merge_requests/index.md

@@ -29,12 +29,12 @@ With GitLab merge requests, you can:
 - Enable [semi-linear history merge requests](#semi-linear-history-merge-requests) as another security layer to guarantee the pipeline is passing in the target branch
 - [Create new merge requests by email](#create-new-merge-requests-by-email)
 - Allow maintainers of the target project to push directly to the fork by [allowing edits from maintainers](maintainer_access.md)
+- [Squash and merge](squash_and_merge.md) for a cleaner commit history
 
 With **[GitLab Enterprise Edition][ee]**, you can also:
 
 - View the deployment process across projects with [Multi-Project Pipeline Graphs](https://docs.gitlab.com/ee/ci/multi_project_pipeline_graphs.html#multi-project-pipeline-graphs) **[PREMIUM]**
 - Request [approvals](https://docs.gitlab.com/ee/user/project/merge_requests/merge_request_approvals.html) from your managers **[STARTER]**
-- [Squash and merge](https://docs.gitlab.com/ee/user/project/merge_requests/squash_and_merge.html) for a cleaner commit history **[STARTER]**
 - Analyze the impact of your changes with [Code Quality reports](https://docs.gitlab.com/ee/user/project/merge_requests/code_quality_diff.html) **[STARTER]**
 
 ## Use cases
@@ -57,7 +57,7 @@ B. Consider you're a web developer writing a webpage for your company's:
 1. Your changes are previewed with [Review Apps](../../../ci/review_apps/index.md)
 1. You request your web designers for their implementation
 1. You request the [approval](https://docs.gitlab.com/ee/user/project/merge_requests/merge_request_approvals.html) from your manager **[STARTER]**
-1. Once approved, your merge request is [squashed and merged](https://docs.gitlab.com/ee/user/project/merge_requests/squash_and_merge.html), and [deployed to staging with GitLab Pages](https://about.gitlab.com/2016/08/26/ci-deployment-and-environments/) (Squash and Merge is available in GitLab Starter)
+1. Once approved, your merge request is [squashed and merged](squash_and_merge.md), and [deployed to staging with GitLab Pages](https://about.gitlab.com/2016/08/26/ci-deployment-and-environments/)
 1. Your production team [cherry picks](#cherry-pick-changes) the merge commit into production
 
 ## Merge requests per project

doc/user/project/merge_requests/squash_and_merge.md

+# Squash and merge
+
+> [Introduced][ee-1024] in [GitLab Starter][ee] 8.17, and in [GitLab CE][ce] [11.0][ce-18956].
+
+Combine all commits of your merge request into one and retain a clean history.
+
+## Overview
+
+Squashing lets you tidy up the commit history of a branch when accepting a merge
+request. It applies all of the changes in the merge request as a single commit,
+and then merges that commit using the merge method set for the project.
+
+In other words, squashing a merge request turns a long list of commits:
+
+![List of commits from a merge request][mr-commits]
+
+Into a single commit on merge:
+
+![A squashed commit followed by a merge commit][squashed-commit]
+
+The squashed commit's commit message is the merge request title. And note that 
+the squashed commit is still followed by a merge commit, as the merge
+method for this example repository uses a merge commit. Squashing also works
+with the fast-forward merge strategy, see
+[squashing and fast-forward merge](#squash-and-fast-forward-merge) for more
+details.
+
+## Use cases
+
+When working on a feature branch, you sometimes want to commit your current
+progress, but don't really care about the commit messages. Those 'work in
+progress commits' don't necessarily contain important information and as such
+you'd rather not include them in your target branch. 
+
+With squash and merge, when the merge request is ready to be merged,
+all you have to do is enable squashing before you press merge to join
+the commits include in the merge request into a single commit.
+
+This way, the history of your base branch remains clean with
+meaningful commit messages and is simpler to [revert] if necessary.
+
+## Enabling squash for a merge request
+
+Anyone who can create or edit a merge request can choose for it to be squashed
+on the merge request form:
+
+![Squash commits checkbox on edit form][squash-edit-form]
+
+---
+
+This can then be overridden at the time of accepting the merge request:
+
+![Squash commits checkbox on accept merge request form][squash-mr-widget]
+
+## Commit metadata for squashed commits
+
+The squashed commit has the following metadata:
+
+* Message: the title of the merge request.
+* Author: the author of the merge request.
+* Committer: the user who initiated the squash.
+
+## Squash and fast-forward merge
+
+When a project has the [fast-forward merge setting enabled][ff-merge], the merge
+request must be able to be fast-forwarded without squashing in order to squash
+it. This is because squashing is only available when accepting a merge request,
+so a merge request may need to be rebased before squashing, even though
+squashing can itself be considered equivalent to rebasing.
+
+[ee-1024]: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1024
+[ce-18956]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18956
+[mr-commits]: img/squash_mr_commits.png
+[squashed-commit]: img/squash_squashed_commit.png
+[squash-edit-form]: img/squash_edit_form.png
+[squash-mr-widget]: img/squash_mr_widget.png
+[ff-merge]: fast_forward_merge.md#enabling-fast-forward-merges
+[ce]: https://about.gitlab.com/products/
+[ee]: https://about.gitlab.com/products/
+[revert]: revert_changes.md

lib/api/entities.rb

@@ -568,6 +568,8 @@ class MergeRequestBasic < ProjectEntity
       expose :time_stats, using: 'API::Entities::IssuableTimeStats' do |merge_request|
         merge_request
       end
+
+      expose :squash
     end
 
     class MergeRequest < MergeRequestBasic

lib/api/merge_requests.rb

@@ -10,12 +10,6 @@ class MergeRequests < Grape::API
     helpers do
       params :optional_params_ee do
       end
-
-      params :merge_params_ee do
-      end
-
-      def update_merge_request_ee(merge_request)
-      end
     end
 
     def self.update_params_at_least_one_of
@@ -29,6 +23,7 @@ def self.update_params_at_least_one_of
         target_branch
         title
         discussion_locked
+        squash
       ]
     end
 
@@ -146,6 +141,7 @@ def handle_merge_request_errors!(errors)
           optional :labels, type: String, desc: 'Comma-separated list of label names'
           optional :remove_source_branch, type: Boolean, desc: 'Remove source branch when merging'
           optional :allow_maintainer_to_push, type: Boolean, desc: 'Whether a maintainer of the target project can push to the source project'
+          optional :squash, type: Grape::API::Boolean, desc: 'When true, the commits will be squashed into a single commit on merge'
 
           use :optional_params_ee
         end
@@ -308,8 +304,7 @@ def handle_merge_request_errors!(errors)
         optional :merge_when_pipeline_succeeds, type: Boolean,
                                                 desc: 'When true, this merge request will be merged when the pipeline succeeds'
         optional :sha, type: String, desc: 'When present, must have the HEAD SHA of the source branch'
-
-        use :merge_params_ee
+        optional :squash, type: Grape::API::Boolean, desc: 'When true, the commits will be squashed into a single commit on merge'
       end
       put ':id/merge_requests/:merge_request_iid/merge' do
         Gitlab::QueryLimiting.whitelist('https://gitlab.com/gitlab-org/gitlab-ce/issues/42317')
@@ -327,7 +322,7 @@ def handle_merge_request_errors!(errors)
 
         check_sha_param!(params, merge_request)
 
-        update_merge_request_ee(merge_request)
+        merge_request.update(squash: params[:squash]) if params[:squash]
 
         merge_params = {