Merge branch 'merge-request-sha-info' into 'master'

Merge request sha info

## What does this MR do?

Exposes `sha` and `merge_commit_sha` items in `MergeRequest` API endpoint data.

## Are there points in the code the reviewer needs to double check?

No.

## Why was this MR needed?

It's useful information.

## What are the relevant issue numbers?

Closes #20456.

## Screenshots (if relevant)

N/A

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5966

4 files changed, 33 insertions, 3 deletions

diff --git a/CHANGELOG b/CHANGELOG
index 39aec111f37..227f4e97dfe 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -11,6 +11,7 @@ v 8.12.0 (unreleased)
   - Change merge_error column from string to text type
   - Reduce contributions calendar data payload (ClemMakesApps)
   - Add `web_url` field to issue, merge request, and snippet API objects (Ben Boeckel)
+  - Expose `sha` and `merge_commit_sha` in merge request API (Ben Boeckel)
   - Set path for all JavaScript cookies to honor GitLab's subdirectory setting !5627 (Mike Greiling)
   - Fix bug where pagination is still displayed despite all todos marked as done (ClemMakesApps)
   - Shorten task status phrase (ClemMakesApps)
diff --git a/doc/api/merge_requests.md b/doc/api/merge_requests.md
index f4760ceac7c..494040a1ce8 100644
--- a/doc/api/merge_requests.md
+++ b/doc/api/merge_requests.md
@@ -68,6 +68,8 @@ Parameters:
     "merge_when_build_succeeds": true,
     "merge_status": "can_be_merged",
     "subscribed" : false,
+    "sha": "8888888888888888888888888888888888888888",
+    "merge_commit_sha": null,
     "user_notes_count": 1,
     "should_remove_source_branch": true,
     "force_remove_source_branch": false,
@@ -135,6 +137,8 @@ Parameters:
   "merge_when_build_succeeds": true,
   "merge_status": "can_be_merged",
   "subscribed" : true,
+  "sha": "8888888888888888888888888888888888888888",
+  "merge_commit_sha": "9999999999999999999999999999999999999999",
   "user_notes_count": 1,
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
@@ -238,6 +242,8 @@ Parameters:
   "merge_when_build_succeeds": true,
   "merge_status": "can_be_merged",
   "subscribed" : true,
+  "sha": "8888888888888888888888888888888888888888",
+  "merge_commit_sha": null,
   "user_notes_count": 1,
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
@@ -322,6 +328,8 @@ Parameters:
   "merge_when_build_succeeds": true,
   "merge_status": "can_be_merged",
   "subscribed" : true,
+  "sha": "8888888888888888888888888888888888888888",
+  "merge_commit_sha": null,
   "user_notes_count": 0,
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
@@ -397,6 +405,8 @@ Parameters:
   "merge_when_build_succeeds": true,
   "merge_status": "can_be_merged",
   "subscribed" : true,
+  "sha": "8888888888888888888888888888888888888888",
+  "merge_commit_sha": null,
   "user_notes_count": 1,
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
@@ -499,6 +509,8 @@ Parameters:
   "merge_when_build_succeeds": true,
   "merge_status": "can_be_merged",
   "subscribed" : true,
+  "sha": "8888888888888888888888888888888888888888",
+  "merge_commit_sha": "9999999999999999999999999999999999999999",
   "user_notes_count": 1,
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
@@ -569,6 +581,8 @@ Parameters:
   "merge_when_build_succeeds": true,
   "merge_status": "can_be_merged",
   "subscribed" : true,
+  "sha": "8888888888888888888888888888888888888888",
+  "merge_commit_sha": null,
   "user_notes_count": 1,
   "should_remove_source_branch": true,
   "force_remove_source_branch": false,
@@ -724,7 +738,9 @@ Example response:
   },
   "merge_when_build_succeeds": false,
   "merge_status": "cannot_be_merged",
-  "subscribed": true
+  "subscribed": true,
+  "sha": "8888888888888888888888888888888888888888",
+  "merge_commit_sha": null
 }
 ```
 
@@ -798,7 +814,9 @@ Example response:
   },
   "merge_when_build_succeeds": false,
   "merge_status": "cannot_be_merged",
-  "subscribed": false
+  "subscribed": false,
+  "sha": "8888888888888888888888888888888888888888",
+  "merge_commit_sha": null
 }
 ```
 
@@ -891,6 +909,8 @@ Example response:
     "merge_when_build_succeeds": false,
     "merge_status": "unchecked",
     "subscribed": true,
+    "sha": "8888888888888888888888888888888888888888",
+    "merge_commit_sha": null,
     "user_notes_count": 7,
     "should_remove_source_branch": true,
     "force_remove_source_branch": false,
diff --git a/lib/api/entities.rb b/lib/api/entities.rb
index fe7468dd681..cfe7a5ca2e1 100644
--- a/lib/api/entities.rb
+++ b/lib/api/entities.rb
@@ -233,6 +233,8 @@ module API
       expose :milestone, using: Entities::Milestone
       expose :merge_when_build_succeeds
       expose :merge_status
+      expose :diff_head_sha, as: :sha
+      expose :merge_commit_sha
       expose :subscribed do |merge_request, options|
         merge_request.subscribed?(options[:current_user])
       end
diff --git a/spec/requests/api/merge_requests_spec.rb b/spec/requests/api/merge_requests_spec.rb
index baff872e28e..a7930c59df9 100644
--- a/spec/requests/api/merge_requests_spec.rb
+++ b/spec/requests/api/merge_requests_spec.rb
@@ -9,7 +9,7 @@ describe API::API, api: true  do
   let!(:project)    { create(:project, creator_id: user.id, namespace: user.namespace) }
   let!(:merge_request) { create(:merge_request, :simple, author: user, assignee: user, source_project: project, target_project: project, title: "Test", created_at: base_time) }
   let!(:merge_request_closed) { create(:merge_request, state: "closed", author: user, assignee: user, source_project: project, target_project: project, title: "Closed test", created_at: base_time + 1.second) }
-  let!(:merge_request_merged) { create(:merge_request, state: "merged", author: user, assignee: user, source_project: project, target_project: project, title: "Merged test", created_at: base_time + 2.seconds) }
+  let!(:merge_request_merged) { create(:merge_request, state: "merged", author: user, assignee: user, source_project: project, target_project: project, title: "Merged test", created_at: base_time + 2.seconds, merge_commit_sha: '9999999999999999999999999999999999999999') }
   let!(:note)       { create(:note_on_merge_request, author: user, project: project, noteable: merge_request, note: "a comment on a MR") }
   let!(:note2)      { create(:note_on_merge_request, author: user, project: project, noteable: merge_request, note: "another comment on a MR") }
   let(:milestone)   { create(:milestone, title: '1.0.0', project: project) }
@@ -34,6 +34,13 @@ describe API::API, api: true  do
         expect(json_response.length).to eq(3)
         expect(json_response.last['title']).to eq(merge_request.title)
         expect(json_response.last).to have_key('web_url')
+        expect(json_response.last['sha']).to eq(merge_request.diff_head_sha)
+        expect(json_response.last['merge_commit_sha']).to be_nil
+        expect(json_response.last['merge_commit_sha']).to eq(merge_request.merge_commit_sha)
+        expect(json_response.first['title']).to eq(merge_request_merged.title)
+        expect(json_response.first['sha']).to eq(merge_request_merged.diff_head_sha)
+        expect(json_response.first['merge_commit_sha']).not_to be_nil
+        expect(json_response.first['merge_commit_sha']).to eq(merge_request_merged.merge_commit_sha)
       end
 
       it "returns an array of all merge_requests" do