Merge branch 'api-version' into 'master'

API: Version information

## What does this MR do?

Adds a new endpoint to retrieve the version information.

## Why was this MR needed?

Clients can now use this information to enable/disable certain API features depending on the version.  

## What are the relevant issue numbers?

Closes #22608, https://gitlab.com/gitlab-org/gitlab-ce/issues/23148

See merge request !6822

CHANGELOG

@@ -32,6 +32,7 @@ v 8.13.0 (unreleased)
   - Cache rendered markdown in the database, rather than Redis
   - Avoid database queries on Banzai::ReferenceParser::BaseParser for nodes without references
   - Simplify Mentionable concern instance methods
+  - API: Ability to retrieve version information (Robert Schilling)
   - Fix permission for setting an issue's due date
   - API: Multi-file commit !6096 (mahcsig)
   - Revert "Label list shows all issues (opened or closed) with that label"

doc/api/README.md

@@ -48,6 +48,7 @@ following locations:
 - [Todos](todos.md)
 - [Users](users.md)
 - [Validate CI configuration](ci/lint.md)
+- [Version](version.md)
 
 ### Internal CI API
 

doc/api/version.md

+# Version API
+
+>**Note:** This feature was introduced in GitLab 8.13
+
+Retrieve version information for this GitLab instance. Responds `200 OK` for
+authenticated users.
+
+```
+GET /version
+```
+
+```bash
+curl --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/version
+```
+
+Example response:
+
+```json
+{
+  "version": "8.13.0-pre",
+  "revision": "4e963fe"
+}
+```

lib/api/api.rb

@@ -72,6 +72,7 @@ module API
     mount ::API::Triggers
     mount ::API::Users
     mount ::API::Variables
+    mount ::API::Version
 
     route :any, '*path' do
       error!('404 Not Found', 404)

lib/api/version.rb

+module API
+  class Version < Grape::API
+    before { authenticate! }
+
+    desc 'Get the version information of the GitLab instance.' do
+      detail 'This feature was introduced in GitLab 8.13.'
+    end
+    get '/version' do
+      { version: Gitlab::VERSION, revision: Gitlab::REVISION }
+    end
+  end
+end

spec/requests/api/version_spec.rb

+require 'spec_helper'
+
+describe API::API, api: true do
+  include ApiHelpers
+
+  describe 'GET /version' do
+    context 'when unauthenticated' do
+      it 'returns authentication error' do
+        get api('/version')
+
+        expect(response).to have_http_status(401)
+      end
+    end
+
+    context 'when authenticated' do
+      let(:user) { create(:user) }
+
+      it 'returns the version information' do
+        get api('/version', user)
+
+        expect(response).to have_http_status(200)
+        expect(json_response['version']).to eq(Gitlab::VERSION)
+        expect(json_response['revision']).to eq(Gitlab::REVISION)
+      end
+    end
+  end
+end