Add changes_count to the merge requests API

This returns the `real_size` of the MR's diff, which is a string indicating the
number of changes. If the diff overflows after _n_ files, the string will be
`$n+`.

changelogs/unreleased/add-changes-count-to-merge-requests-api.yml

+---
+title: Add a count of changes to the merge requests API
+merge_request:
+author:
+type: changed

doc/api/merge_requests.md

@@ -15,6 +15,11 @@ given state (`opened`, `closed`, or `merged`) or all of them (`all`).
 The pagination parameters `page` and `per_page` can be used to
 restrict the list of merge requests.
 
+**Note**: the `changes_count` value in the response is a string, not an
+integer. This is because when an MR has too many changes to display and store,
+it will be capped at 1,000. In that case, the API will return the string
+`"1000+"` for the changes count.
+
 ```
 GET /merge_requests
 GET /merge_requests?state=opened
@@ -92,6 +97,7 @@ Parameters:
     "sha": "8888888888888888888888888888888888888888",
     "merge_commit_sha": null,
     "user_notes_count": 1,
+    "changes_count": "1",
     "should_remove_source_branch": true,
     "force_remove_source_branch": false,
     "web_url": "http://example.com/example/example/merge_requests/1",
@@ -130,6 +136,11 @@ will be the same. In the case of a merge request from a fork,
 `target_project_id` and `project_id` will be the same and
 `source_project_id` will be the fork project's ID.
 
+**Note**: the `changes_count` value in the response is a string, not an
+integer. This is because when an MR has too many changes to display and store,
+it will be capped at 1,000. In that case, the API will return the string
+`"1000+"` for the changes count.
+
 Parameters:
 
 | Attribute           | Type           | Required | Description                                                                                                                    |
@@ -198,6 +209,7 @@ Parameters:
     "sha": "8888888888888888888888888888888888888888",
     "merge_commit_sha": null,
     "user_notes_count": 1,
+    "changes_count": "1",
     "should_remove_source_branch": true,
     "force_remove_source_branch": false,
     "web_url": "http://example.com/example/example/merge_requests/1",
@@ -274,6 +286,7 @@ Parameters:
   "sha": "8888888888888888888888888888888888888888",
   "merge_commit_sha": "9999999999999999999999999999999999999999",
   "user_notes_count": 1,
+  "changes_count": "1",
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
   "web_url": "http://example.com/example/example/merge_requests/1",
@@ -386,6 +399,7 @@ Parameters:
   "sha": "8888888888888888888888888888888888888888",
   "merge_commit_sha": null,
   "user_notes_count": 1,
+  "changes_count": "1",
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
   "web_url": "http://example.com/example/example/merge_requests/1",
@@ -480,6 +494,7 @@ POST /projects/:id/merge_requests
   "sha": "8888888888888888888888888888888888888888",
   "merge_commit_sha": null,
   "user_notes_count": 0,
+  "changes_count": "1",
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
   "web_url": "http://example.com/example/example/merge_requests/1",
@@ -565,6 +580,7 @@ Must include at least one non-required attribute from above.
   "sha": "8888888888888888888888888888888888888888",
   "merge_commit_sha": null,
   "user_notes_count": 1,
+  "changes_count": "1",
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
   "web_url": "http://example.com/example/example/merge_requests/1",
@@ -670,6 +686,7 @@ Parameters:
   "sha": "8888888888888888888888888888888888888888",
   "merge_commit_sha": "9999999999999999999999999999999999999999",
   "user_notes_count": 1,
+  "changes_count": "1",
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
   "web_url": "http://example.com/example/example/merge_requests/1",
@@ -747,6 +764,7 @@ Parameters:
   "sha": "8888888888888888888888888888888888888888",
   "merge_commit_sha": null,
   "user_notes_count": 1,
+  "changes_count": "1",
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
   "web_url": "http://example.com/example/example/merge_requests/1",
@@ -822,7 +840,8 @@ Example response when the GitLab issue tracker is used:
       "created_at" : "2016-01-04T15:31:51.081Z",
       "iid" : 6,
       "labels" : [],
-      "user_notes_count": 1
+      "user_notes_count": 1,
+      "changes_count": "1"
    },
 ]
 ```
@@ -1077,6 +1096,7 @@ Example response:
     "sha": "8888888888888888888888888888888888888888",
     "merge_commit_sha": null,
     "user_notes_count": 7,
+    "changes_count": "1",
     "should_remove_source_branch": true,
     "force_remove_source_branch": false,
     "web_url": "http://example.com/example/example/merge_requests/1"

lib/api/entities.rb

@@ -478,6 +478,10 @@ module API
       expose :subscribed do |merge_request, options|
         merge_request.subscribed?(options[:current_user], options[:project])
       end
+
+      expose :changes_count do |merge_request, _options|
+        merge_request.merge_request_diff.real_size
+      end
     end
 
     class MergeRequestChanges < MergeRequest

spec/fixtures/api/schemas/public_api/v4/merge_requests.json

@@ -70,6 +70,7 @@
       "sha": { "type": "string" },
       "merge_commit_sha": { "type": ["string", "null"] },
       "user_notes_count": { "type": "integer" },
+      "changes_count": { "type": "string" },
       "should_remove_source_branch": { "type": ["boolean", "null"] },
       "force_remove_source_branch": { "type": ["boolean", "null"] },
       "discussion_locked": { "type": ["boolean", "null"] },

spec/requests/api/merge_requests_spec.rb

@@ -435,17 +435,7 @@ describe API::MergeRequests do
       expect(json_response['merge_status']).to eq('can_be_merged')
       expect(json_response['should_close_merge_request']).to be_falsy
       expect(json_response['force_close_merge_request']).to be_falsy
-    end
-
-    it "returns merge_request" do
-      get api("/projects/#{project.id}/merge_requests/#{merge_request.iid}", user)
-      expect(response).to have_gitlab_http_status(200)
-      expect(json_response['title']).to eq(merge_request.title)
-      expect(json_response['iid']).to eq(merge_request.iid)
-      expect(json_response['work_in_progress']).to eq(false)
-      expect(json_response['merge_status']).to eq('can_be_merged')
-      expect(json_response['should_close_merge_request']).to be_falsy
-      expect(json_response['force_close_merge_request']).to be_falsy
+      expect(json_response['changes_count']).to eq(merge_request.merge_request_diff.real_size)
     end
 
     it "returns a 404 error if merge_request_iid not found" do
@@ -462,12 +452,32 @@ describe API::MergeRequests do
     context 'Work in Progress' do
       let!(:merge_request_wip) { create(:merge_request, author: user, assignee: user, source_project: project, target_project: project, title: "WIP: Test", created_at: base_time + 1.second) }
 
-      it "returns merge_request" do
+      it "returns merge request" do
         get api("/projects/#{project.id}/merge_requests/#{merge_request_wip.iid}", user)
+
         expect(response).to have_gitlab_http_status(200)
         expect(json_response['work_in_progress']).to eq(true)
       end
     end
+
+    context 'when a merge request has more than the changes limit' do
+      it "returns a string indicating that more changes were made" do
+        stub_const('Commit::DIFF_HARD_LIMIT_FILES', 5)
+
+        merge_request_overflow = create(:merge_request, :simple,
+                                        author: user,
+                                        assignee: user,
+                                        source_project: project,
+                                        source_branch: 'expand-collapse-files',
+                                        target_project: project,
+                                        target_branch: 'master')
+
+        get api("/projects/#{project.id}/merge_requests/#{merge_request_overflow.iid}", user)
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(json_response['changes_count']).to eq('5+')
+      end
+    end
   end
 
   describe 'GET /projects/:id/merge_requests/:merge_request_iid/commits' do