Configurable defaults for "Squash commits" option

Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/17613

This commit adds the capability to set squash commits options.
The configuration is done on a project settings level.
It allows configuration for squashing commits before merging.

app/helpers/issuables_helper.rb

@@ -385,6 +385,14 @@ module IssuablesHelper
     end
   end
 
+  def issuable_squash_option?(issuable, project)
+    if issuable.persisted?
+      issuable.squash
+    else
+      project.squash_enabled_by_default?
+    end
+  end
+
   private
 
   def sidebar_gutter_collapsed?

app/views/projects/_merge_request_settings.html.haml

@@ -4,6 +4,9 @@
 
 = render 'projects/merge_request_merge_options_settings', project: @project, form: form
 
+- if Feature.enabled?(:squash_options, @project)
+  = render 'projects/merge_request_squash_options_settings', form: form
+
 = render 'projects/merge_request_merge_checks_settings', project: @project, form: form
 
 = render 'projects/merge_request_merge_suggestions_settings', project: @project, form: form

app/views/projects/_merge_request_squash_options_settings.html.haml

+- form = local_assigns.fetch(:form)
+
+= form.fields_for :project_setting do |settings|
+  .form-group
+    %b= s_('ProjectSettings|Squash commits when merging')
+    %p.text-secondary
+      = s_('ProjectSettings|Set the default behavior and availability of this option in merge requests. Changes made are also applied to existing merge requests.')
+      = link_to "What is squashing?",
+        help_page_path('user/project/merge_requests/squash_and_merge.md'),
+        target: '_blank'
+
+    .form-check.gl-mb-2
+      = settings.radio_button :squash_option, :never, class: "form-check-input"
+      = label_tag :project_project_setting_attributes_squash_option_never, class: 'form-check-label' do
+        .gl-font-weight-bold
+          = s_('ProjectSettings|Do not allow')
+        .text-secondary
+          = s_('ProjectSettings|Squashing is never performed and the checkbox is hidden.')
+
+    .form-check.gl-mb-2
+      = settings.radio_button :squash_option, :default_off, class: "form-check-input"
+      = label_tag :project_project_setting_attributes_squash_option_default_off, class: 'form-check-label' do
+        .gl-font-weight-bold
+          = s_('ProjectSettings|Allow')
+        .text-secondary
+          = s_('ProjectSettings|Checkbox is visible and unselected by default.')
+
+    .form-check.gl-mb-2
+      = settings.radio_button :squash_option, :default_on, class: "form-check-input"
+      = label_tag :project_project_setting_attributes_squash_option_default_on, class: 'form-check-label' do
+        .gl-font-weight-bold
+          = s_('ProjectSettings|Encourage')
+        .text-secondary
+          = s_('ProjectSettings|Checkbox is visible and selected by default.')
+
+    .form-check.gl-mb-2
+      = settings.radio_button :squash_option, :always, class: "form-check-input"
+      = label_tag :project_project_setting_attributes_squash_option_always, class: 'form-check-label' do
+        .gl-font-weight-bold
+          = s_('ProjectSettings|Require')
+        .text-secondary
+          = s_('ProjectSettings|Squashing is always performed. Checkbox is visible and selected, and users cannot change it.')

app/views/shared/issuable/_form.html.haml

@@ -35,7 +35,7 @@
 
 = render_if_exists 'shared/issuable/approvals', issuable: issuable, presenter: presenter, form: form
 
-= render 'shared/issuable/form/merge_params', issuable: issuable
+= render 'shared/issuable/form/merge_params', issuable: issuable, project: project
 
 = render 'shared/issuable/form/contribution', issuable: issuable, form: form
 

app/views/shared/issuable/form/_merge_params.html.haml

 - issuable = local_assigns.fetch(:issuable)
+- project = local_assigns.fetch(:project)
 
 - return unless issuable.is_a?(MergeRequest)
 - return if issuable.closed_without_fork?
@@ -14,9 +15,14 @@
         = check_box_tag 'merge_request[force_remove_source_branch]', '1', issuable.force_remove_source_branch?, class: 'form-check-input'
         = label_tag 'merge_request[force_remove_source_branch]', class: 'form-check-label' do
           Delete source branch when merge request is accepted.
+    - if !project.squash_never?
       .form-check
+        - if project.squash_always?
+          = hidden_field_tag 'merge_request[squash]', '1', id: nil
+          = check_box_tag 'merge_request[squash]', '1', project.squash_enabled_by_default?, class: 'form-check-input', disabled: 'true'
+        - else
           = hidden_field_tag 'merge_request[squash]', '0', id: nil
-      = check_box_tag 'merge_request[squash]', '1', issuable.squash, class: 'form-check-input'
+          = check_box_tag 'merge_request[squash]', '1', issuable_squash_option?(issuable, project), class: 'form-check-input'
         = label_tag 'merge_request[squash]', class: 'form-check-label' do
           Squash commits when merge request is accepted.
           = link_to icon('question-circle'), help_page_path('user/project/merge_requests/squash_and_merge'), target: '_blank'

ee/app/views/projects/_merge_request_settings.html.haml

@@ -4,6 +4,9 @@
 
 = render_ce 'projects/merge_request_merge_options_settings', project: @project, form: form
 
+- if Feature.enabled?(:squash_options, @project)
+  = render_ce 'projects/merge_request_squash_options_settings', form: form
+
 = render_ce 'projects/merge_request_merge_checks_settings', project: @project, form: form
 
 = render 'projects/merge_request_merge_suggestions_settings', project: @project, form: form

locale/gitlab.pot

@@ -17745,6 +17745,9 @@ msgstr ""
 msgid "ProjectSettings|All discussions must be resolved"
 msgstr ""
 
+msgid "ProjectSettings|Allow"
+msgstr ""
+
 msgid "ProjectSettings|Allow users to make copies of your repository to a new project"
 msgstr ""
 
@@ -17760,6 +17763,12 @@ msgstr ""
 msgid "ProjectSettings|Build, test, and deploy your changes"
 msgstr ""
 
+msgid "ProjectSettings|Checkbox is visible and selected by default."
+msgstr ""
+
+msgid "ProjectSettings|Checkbox is visible and unselected by default."
+msgstr ""
+
 msgid "ProjectSettings|Choose your merge method, merge options, merge checks, and merge suggestions."
 msgstr ""
 
@@ -17778,12 +17787,18 @@ msgstr ""
 msgid "ProjectSettings|Disable email notifications"
 msgstr ""
 
+msgid "ProjectSettings|Do not allow"
+msgstr ""
+
 msgid "ProjectSettings|Enable 'Delete source branch' option by default"
 msgstr ""
 
 msgid "ProjectSettings|Enable merge trains and pipelines for merged results"
 msgstr ""
 
+msgid "ProjectSettings|Encourage"
+msgstr ""
+
 msgid "ProjectSettings|Every merge creates a merge commit"
 msgstr ""
 
@@ -17898,6 +17913,12 @@ msgstr ""
 msgid "ProjectSettings|Repository"
 msgstr ""
 
+msgid "ProjectSettings|Require"
+msgstr ""
+
+msgid "ProjectSettings|Set the default behavior and availability of this option in merge requests. Changes made are also applied to existing merge requests."
+msgstr ""
+
 msgid "ProjectSettings|Share code pastes with others out of Git repository"
 msgstr ""
 
@@ -17913,6 +17934,15 @@ msgstr ""
 msgid "ProjectSettings|Snippets"
 msgstr ""
 
+msgid "ProjectSettings|Squash commits when merging"
+msgstr ""
+
+msgid "ProjectSettings|Squashing is always performed. Checkbox is visible and selected, and users cannot change it."
+msgstr ""
+
+msgid "ProjectSettings|Squashing is never performed and the checkbox is hidden."
+msgstr ""
+
 msgid "ProjectSettings|Submit changes to be merged upstream"
 msgstr ""
 

spec/features/projects/settings/user_manages_merge_requests_settings_spec.rb

@@ -28,6 +28,22 @@ RSpec.describe 'Projects > Settings > User manages merge request settings' do
     end
   end
 
+  it 'shows Squash commit options', :aggregate_failures do
+    page.within '#js-merge-request-settings' do
+      expect(page).to have_content 'Do not allow'
+      expect(page).to have_content 'Squashing is never performed and the checkbox is hidden.'
+
+      expect(page).to have_content 'Allow'
+      expect(page).to have_content 'Checkbox is visible and unselected by default.'
+
+      expect(page).to have_content 'Encourage'
+      expect(page).to have_content 'Checkbox is visible and selected by default.'
+
+      expect(page).to have_content 'Require'
+      expect(page).to have_content 'Squashing is always performed. Checkbox is visible and selected, and users cannot change it.'
+    end
+  end
+
   context 'when Merge Request and Pipelines are initially enabled', :js do
     context 'when Pipelines are initially enabled' do
       it 'shows the Merge Requests settings' do
@@ -130,4 +146,56 @@ RSpec.describe 'Projects > Settings > User manages merge request settings' do
       expect(project.remove_source_branch_after_merge).to be(false)
     end
   end
+
+  describe 'Squash commits when merging', :js do
+    it 'initially has :squash_option set to :default_off' do
+      radio = find_field('project_project_setting_attributes_squash_option_default_off')
+      expect(radio).to be_checked
+    end
+
+    it 'allows :squash_option to be set to :default_on' do
+      choose('project_project_setting_attributes_squash_option_default_on')
+
+      within('.merge-request-settings-form') do
+        find('.qa-save-merge-request-changes')
+        click_on('Save changes')
+      end
+
+      find('.flash-notice')
+      radio = find_field('project_project_setting_attributes_squash_option_default_on')
+
+      expect(radio).to be_checked
+      expect(project.reload.project_setting.squash_option).to eq('default_on')
+    end
+
+    it 'allows :squash_option to be set to :always' do
+      choose('project_project_setting_attributes_squash_option_always')
+
+      within('.merge-request-settings-form') do
+        find('.qa-save-merge-request-changes')
+        click_on('Save changes')
+      end
+
+      find('.flash-notice')
+      radio = find_field('project_project_setting_attributes_squash_option_always')
+
+      expect(radio).to be_checked
+      expect(project.reload.project_setting.squash_option).to eq('always')
+    end
+
+    it 'allows :squash_option to be set to :never' do
+      choose('project_project_setting_attributes_squash_option_never')
+
+      within('.merge-request-settings-form') do
+        find('.qa-save-merge-request-changes')
+        click_on('Save changes')
+      end
+
+      find('.flash-notice')
+      radio = find_field('project_project_setting_attributes_squash_option_never')
+
+      expect(radio).to be_checked
+      expect(project.reload.project_setting.squash_option).to eq('never')
+    end
+  end
 end

spec/helpers/issuables_helper_spec.rb

@@ -303,4 +303,28 @@ RSpec.describe IssuablesHelper do
       end
     end
   end
+
+  describe '#issuable_squash_option?' do
+    using RSpec::Parameterized::TableSyntax
+
+    where(:issuable_persisted, :squash, :squash_enabled_by_default, :expectation) do
+      true  | true  | true  | true
+      true  | false | true  | false
+      false | false | false | false
+      false | false | true  | true
+      false | true  | false | false
+      false | true  | true  | true
+    end
+
+    with_them do
+      it 'returns the correct value' do
+        project = double(
+          squash_enabled_by_default?: squash_enabled_by_default
+        )
+        issuable = double(persisted?: issuable_persisted, squash: squash)
+
+        expect(helper.issuable_squash_option?(issuable, project)).to eq(expectation)
+      end
+    end
+  end
 end