Add ability to set `squash_option` in the Project API

Changelog: added

app/models/project.rb

@@ -417,7 +417,7 @@ class Project < ApplicationRecord
   delegate :scheduled?, :started?, :in_progress?, :failed?, :finished?,
     prefix: :import, to: :import_state, allow_nil: true
   delegate :squash_always?, :squash_never?, :squash_enabled_by_default?, :squash_readonly?, to: :project_setting
-  delegate :squash_option, to: :project_setting
+  delegate :squash_option, :squash_option=, to: :project_setting
   delegate :previous_default_branch, :previous_default_branch=, to: :project_setting
   delegate :no_import?, to: :import_state, allow_nil: true
   delegate :name, to: :owner, allow_nil: true, prefix: true

app/policies/project_policy.rb

@@ -225,6 +225,7 @@ class ProjectPolicy < BasePolicy
     enable :set_note_created_at
     enable :set_emails_disabled
     enable :set_show_default_award_emojis
+    enable :set_squash_option
   end
 
   rule { can?(:guest_access) }.policy do

doc/api/projects.md

@@ -1215,6 +1215,7 @@ POST /projects
 | `show_default_award_emojis`                                 | boolean | **{dotted-circle}** No | Show default award emojis. |
 | `snippets_access_level`                                     | string  | **{dotted-circle}** No | One of `disabled`, `private`, or `enabled`. |
 | `snippets_enabled`                                          | boolean | **{dotted-circle}** No | _(Deprecated)_ Enable snippets for this project. Use `snippets_access_level` instead. |
+| `squash_option`                                             | string  | **{dotted-circle}** No | One of `never`, `always`, `default_on`, or `default_off`. |
 | `tag_list`                                                  | array   | **{dotted-circle}** No | _([Deprecated](https://gitlab.com/gitlab-org/gitlab/-/issues/328226) in GitLab 14.0)_ The list of tags for a project; put array of tags, that should be finally assigned to a project. Use `topics` instead. |
 | `template_name`                                             | string  | **{dotted-circle}** No | When used without `use_custom_template`, name of a [built-in project template](../user/project/working_with_projects.md#built-in-templates). When used with `use_custom_template`, name of a custom project template. |
 | `template_project_id` **(PREMIUM)**                         | integer | **{dotted-circle}** No | When used with `use_custom_template`, project ID of a custom project template. This is preferable to using `template_name` since `template_name` may be ambiguous. |
@@ -1290,6 +1291,7 @@ POST /projects/user/:user_id
 | `show_default_award_emojis`                                 | boolean | **{dotted-circle}** No | Show default award emojis. |
 | `snippets_access_level`                                     | string  | **{dotted-circle}** No | One of `disabled`, `private`, or `enabled`. |
 | `snippets_enabled`                                          | boolean | **{dotted-circle}** No | _(Deprecated)_ Enable snippets for this project. Use `snippets_access_level` instead. |
+| `squash_option`                                             | string  | **{dotted-circle}** No | One of `never`, `always`, `default_on`, or `default_off`. |
 | `suggestion_commit_message`                                 | string  | **{dotted-circle}** No | The commit message used to apply merge request [suggestions](../user/project/merge_requests/reviews/suggestions.md). |
 | `tag_list`                                                  | array   | **{dotted-circle}** No | _([Deprecated](https://gitlab.com/gitlab-org/gitlab/-/issues/328226) in GitLab 14.0)_ The list of tags for a project; put array of tags, that should be finally assigned to a project. Use `topics` instead. |
 | `template_name`                                             | string  | **{dotted-circle}** No | When used without `use_custom_template`, name of a [built-in project template](../user/project/working_with_projects.md#built-in-templates). When used with `use_custom_template`, name of a custom project template. |
@@ -1369,6 +1371,7 @@ PUT /projects/:id
 | `show_default_award_emojis`                                 | boolean        | **{dotted-circle}** No | Show default award emojis. |
 | `snippets_access_level`                                     | string         | **{dotted-circle}** No | One of `disabled`, `private`, or `enabled`. |
 | `snippets_enabled`                                          | boolean        | **{dotted-circle}** No | _(Deprecated)_ Enable snippets for this project. Use `snippets_access_level` instead. |
+| `squash_option`                                             | string         | **{dotted-circle}** No | One of `never`, `always`, `default_on`, or `default_off`. |
 | `suggestion_commit_message`                                 | string         | **{dotted-circle}** No | The commit message used to apply merge request suggestions. |
 | `tag_list`                                                  | array          | **{dotted-circle}** No | _([Deprecated](https://gitlab.com/gitlab-org/gitlab/-/issues/328226) in GitLab 14.0)_ The list of tags for a project; put array of tags, that should be finally assigned to a project. Use `topics` instead. |
 | `topics`                                                    | array          | **{dotted-circle}** No | The list of topics for the project. This replaces any existing topics that are already added to the project. _([Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/328226) in GitLab 14.0.)_ |

lib/api/helpers/projects_helpers.rb

@@ -66,6 +66,7 @@ module API
         optional :autoclose_referenced_issues, type: Boolean, desc: 'Flag indication if referenced issues auto-closing is enabled'
         optional :repository_storage, type: String, desc: 'Which storage shard the repository is on. Available only to admins'
         optional :packages_enabled, type: Boolean, desc: 'Enable project packages feature'
+        optional :squash_option, type: String, values: %w(never always default_on default_off), desc: 'Squash default for project. One of `never`, `always`, `default_on`, or `default_off`.'
       end
 
       params :optional_project_params_ee do
@@ -145,6 +146,7 @@ module API
           :request_access_enabled,
           :resolve_outdated_diff_discussions,
           :restrict_user_defined_variables,
+          :squash_option,
           :shared_runners_enabled,
           :snippets_access_level,
           :tag_list,

spec/requests/api/projects_spec.rb

@@ -999,7 +999,8 @@ RSpec.describe API::Projects do
         request_access_enabled: true,
         only_allow_merge_if_all_discussions_are_resolved: false,
         ci_config_path: 'a/custom/path',
-        merge_method: 'ff'
+        merge_method: 'ff',
+        squash_option: 'always'
       }).tap do |attrs|
         attrs[:operations_access_level] = 'disabled'
         attrs[:analytics_access_level] = 'disabled'
@@ -3136,6 +3137,24 @@ RSpec.describe API::Projects do
 
         expect(json_response['topics']).to eq(%w[topic2])
       end
+
+      it 'updates squash_option' do
+        project_param = { squash_option: "default_on" }
+
+        put api("/projects/#{project3.id}", user), params: project_param
+
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(project3.reload.squash_option).to eq("default_on")
+        expect(json_response['squash_option']).to eq("default_on")
+      end
+
+      it 'does not update an invalid squash_option' do
+        project_param = { squash_option: "jawn" }
+
+        put api("/projects/#{project3.id}", user), params: project_param
+
+        expect(response).to have_gitlab_http_status(:bad_request)
+      end
     end
 
     context 'when authenticated as project maintainer' do