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 @@ class Projects::MergeRequests::ApplicationController < Projects::ApplicationCont
       :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 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
   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 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
     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 @@ module MergeRequestsHelper
     {
       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 @@ module MergeRequestsHelper
       current_user.fork_of(project)
     end
   end
-
-  def merge_params_ee(merge_request)
-    {}
-  end
 end

app/models/merge_request.rb

@@ -1140,4 +1140,11 @@ class MergeRequest < ActiveRecord::Base
     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 @@ class Repository
                                        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 @@ module MergeRequests
       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 @@ module MergeRequests
     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 @@ ActiveRecord::Schema.define(version: 20180521171529) do
     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",