Resolve "Allow the configuration of a project's merge method via the API"

changelogs/unreleased/39880-merge-method-api.yml

+---
+title: 'API: Add parameter merge_method to projects'
+merge_request: 18031
+author: Jan Beckmann
+type: added

doc/api/projects.md

@@ -16,6 +16,21 @@ Values for the project visibility level are:
 * `public`:
   The project can be cloned without any authentication.
 
+## Project merge method
+
+There are currently three options for `merge_method` to choose from:
+
+* `merge`:
+  A merge commit is created for every merge, and merging is allowed as long as there are no conflicts.
+
+* `rebase_merge`:
+  A merge commit is created for every merge, but merging is only allowed if fast-forward merge is possible.
+  This way you could make sure that if this merge request would build, after merging to target branch it would also build.
+
+* `ff`:
+  No merge commits are created and all merges are fast-forwarded, which means that merging is only allowed if the branch could be fast-forwarded.
+
+
 ## List all projects
 
 Get a list of all visible projects across GitLab for the authenticated user.
@@ -94,6 +109,7 @@ GET /projects
     "only_allow_merge_if_pipeline_succeeds": false,
     "only_allow_merge_if_all_discussions_are_resolved": false,
     "request_access_enabled": false,
+    "merge_method": "merge",
     "statistics": {
       "commit_count": 37,
       "storage_size": 1038090,
@@ -173,6 +189,7 @@ GET /projects
     "only_allow_merge_if_pipeline_succeeds": false,
     "only_allow_merge_if_all_discussions_are_resolved": false,
     "request_access_enabled": false,
+    "merge_method": "merge",
     "statistics": {
       "commit_count": 12,
       "storage_size": 2066080,
@@ -278,6 +295,7 @@ GET /users/:user_id/projects
     "only_allow_merge_if_pipeline_succeeds": false,
     "only_allow_merge_if_all_discussions_are_resolved": false,
     "request_access_enabled": false,
+    "merge_method": "merge",
     "statistics": {
       "commit_count": 37,
       "storage_size": 1038090,
@@ -357,6 +375,7 @@ GET /users/:user_id/projects
     "only_allow_merge_if_pipeline_succeeds": false,
     "only_allow_merge_if_all_discussions_are_resolved": false,
     "request_access_enabled": false,
+    "merge_method": "merge",
     "statistics": {
       "commit_count": 12,
       "storage_size": 2066080,
@@ -467,6 +486,7 @@ GET /projects/:id
   "only_allow_merge_if_all_discussions_are_resolved": false,
   "printing_merge_requests_link_enabled": true,
   "request_access_enabled": false,
+  "merge_method": "merge",
   "statistics": {
     "commit_count": 37,
     "storage_size": 1038090,
@@ -550,6 +570,7 @@ POST /projects
 | `public_jobs` | boolean | no | If `true`, jobs can be viewed by non-project-members |
 | `only_allow_merge_if_pipeline_succeeds` | boolean | no | Set whether merge requests can only be merged with successful jobs |
 | `only_allow_merge_if_all_discussions_are_resolved` | boolean | no | Set whether merge requests can only be merged when all the discussions are resolved |
+| `merge_method` | string | no | Set the merge method used |
 | `lfs_enabled` | boolean | no | Enable LFS |
 | `request_access_enabled` | boolean | no | Allow users to request member access |
 | `tag_list`    | array   | no       | The list of tags for a project; put array of tags, that should be finally assigned to a project |
@@ -586,6 +607,7 @@ POST /projects/user/:user_id
 | `public_jobs` | boolean | no | If `true`, jobs can be viewed by non-project-members |
 | `only_allow_merge_if_pipeline_succeeds` | boolean | no | Set whether merge requests can only be merged with successful jobs |
 | `only_allow_merge_if_all_discussions_are_resolved` | boolean | no | Set whether merge requests can only be merged when all the discussions are resolved |
+| `merge_method` | string | no | Set the merge method used |
 | `lfs_enabled` | boolean | no | Enable LFS |
 | `request_access_enabled` | boolean | no | Allow users to request member access |
 | `tag_list`    | array   | no       | The list of tags for a project; put array of tags, that should be finally assigned to a project |
@@ -621,6 +643,7 @@ PUT /projects/:id
 | `public_jobs` | boolean | no | If `true`, jobs can be viewed by non-project-members |
 | `only_allow_merge_if_pipeline_succeeds` | boolean | no | Set whether merge requests can only be merged with successful jobs |
 | `only_allow_merge_if_all_discussions_are_resolved` | boolean | no | Set whether merge requests can only be merged when all the discussions are resolved |
+| `merge_method` | string | no | Set the merge method used |
 | `lfs_enabled` | boolean | no | Enable LFS |
 | `request_access_enabled` | boolean | no | Allow users to request member access |
 | `tag_list`    | array   | no       | The list of tags for a project; put array of tags, that should be finally assigned to a project |
@@ -724,6 +747,7 @@ Example responses:
     "only_allow_merge_if_pipeline_succeeds": false,
     "only_allow_merge_if_all_discussions_are_resolved": false,
     "request_access_enabled": false,
+    "merge_method": "merge",
     "_links": {
       "self": "http://example.com/api/v4/projects",
       "issues": "http://example.com/api/v4/projects/1/issues",
@@ -801,6 +825,7 @@ Example response:
   "only_allow_merge_if_pipeline_succeeds": false,
   "only_allow_merge_if_all_discussions_are_resolved": false,
   "request_access_enabled": false,
+  "merge_method": "merge",
   "_links": {
     "self": "http://example.com/api/v4/projects",
     "issues": "http://example.com/api/v4/projects/1/issues",
@@ -877,6 +902,7 @@ Example response:
   "only_allow_merge_if_pipeline_succeeds": false,
   "only_allow_merge_if_all_discussions_are_resolved": false,
   "request_access_enabled": false,
+  "merge_method": "merge",
   "_links": {
     "self": "http://example.com/api/v4/projects",
     "issues": "http://example.com/api/v4/projects/1/issues",
@@ -971,6 +997,7 @@ Example response:
   "only_allow_merge_if_pipeline_succeeds": false,
   "only_allow_merge_if_all_discussions_are_resolved": false,
   "request_access_enabled": false,
+  "merge_method": "merge",
   "_links": {
     "self": "http://example.com/api/v4/projects",
     "issues": "http://example.com/api/v4/projects/1/issues",
@@ -1065,6 +1092,7 @@ Example response:
   "only_allow_merge_if_pipeline_succeeds": false,
   "only_allow_merge_if_all_discussions_are_resolved": false,
   "request_access_enabled": false,
+  "merge_method": "merge",
   "_links": {
     "self": "http://example.com/api/v4/projects",
     "issues": "http://example.com/api/v4/projects/1/issues",

lib/api/entities.rb

@@ -206,6 +206,7 @@ module API
       expose :request_access_enabled
       expose :only_allow_merge_if_all_discussions_are_resolved
       expose :printing_merge_request_link_enabled
+      expose :merge_method
 
       expose :statistics, using: 'API::Entities::ProjectStatistics', if: :statistics
 

lib/api/projects.rb

@@ -28,6 +28,7 @@ module API
         optional :tag_list, type: Array[String], desc: 'The list of tags for a project'
         optional :avatar, type: File, desc: 'Avatar image for project'
         optional :printing_merge_request_link_enabled, type: Boolean, desc: 'Show link to create/view merge request when pushing from the command line'
+        optional :merge_method, type: String, values: %w(ff rebase_merge merge), desc: 'The merge method used when merging merge requests'
       end
 
       params :optional_params do
@@ -274,6 +275,7 @@ module API
             :issues_enabled,
             :lfs_enabled,
             :merge_requests_enabled,
+            :merge_method,
             :name,
             :only_allow_merge_if_all_discussions_are_resolved,
             :only_allow_merge_if_pipeline_succeeds,

spec/requests/api/projects_spec.rb

@@ -452,7 +452,8 @@ describe API::Projects do
         only_allow_merge_if_pipeline_succeeds: false,
         request_access_enabled: true,
         only_allow_merge_if_all_discussions_are_resolved: false,
-        ci_config_path: 'a/custom/path'
+        ci_config_path: 'a/custom/path',
+        merge_method: 'ff'
       })
 
       post api('/projects', user), project
@@ -569,6 +570,22 @@ describe API::Projects do
       expect(json_response['only_allow_merge_if_all_discussions_are_resolved']).to be_truthy
     end
 
+    it 'sets the merge method of a project to rebase merge' do
+      project = attributes_for(:project, merge_method: 'rebase_merge')
+
+      post api('/projects', user), project
+
+      expect(json_response['merge_method']).to eq('rebase_merge')
+    end
+
+    it 'rejects invalid values for merge_method' do
+      project = attributes_for(:project, merge_method: 'totally_not_valid_method')
+
+      post api('/projects', user), project
+
+      expect(response).to have_gitlab_http_status(400)
+    end
+
     it 'ignores import_url when it is nil' do
       project = attributes_for(:project, import_url: nil)
 
@@ -823,6 +840,7 @@ describe API::Projects do
         expect(json_response['shared_with_groups'][0]['group_access_level']).to eq(link.group_access)
         expect(json_response['only_allow_merge_if_pipeline_succeeds']).to eq(project.only_allow_merge_if_pipeline_succeeds)
         expect(json_response['only_allow_merge_if_all_discussions_are_resolved']).to eq(project.only_allow_merge_if_all_discussions_are_resolved)
+        expect(json_response['merge_method']).to eq(project.merge_method.to_s)
       end
 
       it 'returns a project by path name' do
@@ -1474,6 +1492,26 @@ describe API::Projects do
           expect(json_response[k.to_s]).to eq(v)
         end
       end
+
+      it 'updates merge_method' do
+        project_param = { merge_method: 'ff' }
+
+        put api("/projects/#{project3.id}", user), project_param
+
+        expect(response).to have_gitlab_http_status(200)
+
+        project_param.each_pair do |k, v|
+          expect(json_response[k.to_s]).to eq(v)
+        end
+      end
+
+      it 'rejects to update merge_method when merge_method is invalid' do
+        project_param = { merge_method: 'invalid' }
+
+        put api("/projects/#{project3.id}", user), project_param
+
+        expect(response).to have_gitlab_http_status(400)
+      end
     end
 
     context 'when authenticated as project master' do
@@ -1491,6 +1529,7 @@ describe API::Projects do
                           wiki_enabled: true,
                           snippets_enabled: true,
                           merge_requests_enabled: true,
+                          merge_method: 'ff',
                           description: 'new description' }
 
         put api("/projects/#{project3.id}", user4), project_param