Fallback to lowest visibility level in snippet visibility radio

In snippets form when the default visibility level is not
available fallback to the lowest available visibility level.

app/helpers/visibility_level_helper.rb

@@ -167,6 +167,17 @@ module VisibilityLevelHelper
     [requested_level, max_allowed_visibility_level(form_model)].min
   end
 
+  def available_visibility_levels(form_model)
+    Gitlab::VisibilityLevel.values.reject do |level|
+      disallowed_visibility_level?(form_model, level) ||
+      restricted_visibility_levels.include?(level)
+    end
+  end
+
+  def snippets_selected_visibility_level(visibility_levels, selected)
+    visibility_levels.find { |level| level == selected } || visibility_levels.min
+  end
+
   def multiple_visibility_levels_restricted?
     restricted_visibility_levels.many? # rubocop: disable CodeReuse/ActiveRecord
   end

app/views/shared/_visibility_radios.html.haml

-- Gitlab::VisibilityLevel.values.each do |level|
-  - disallowed = disallowed_visibility_level?(form_model, level)
-  - restricted = restricted_visibility_levels.include?(level)
-  - next if disallowed || restricted
+- available_visibility_levels = available_visibility_levels(form_model)
+- selected_level = snippets_selected_visibility_level(available_visibility_levels, selected_level)
 
+- available_visibility_levels.each do |level|
   .form-check
     = form.radio_button model_method, level, checked: (selected_level == level), class: 'form-check-input', data: { track_label: "blank_project", track_event: "activate_form_input", track_property: "#{model_method}_#{level}", track_value: "", qa_selector: "#{visibility_level_label(level).downcase}_radio" }
     = form.label "#{model_method}_#{level}", class: 'form-check-label' do

changelogs/unreleased/216871-snippets-author-can-t-be-blank-error.yml

+---
+title: Fallback to lowest visibility level in snippet visibility radio
+merge_request: 31847
+author: Jacopo Beschi @jacopo-beschi
+type: fixed

spec/features/snippets/user_creates_snippet_spec.rb

@@ -7,7 +7,6 @@ shared_examples_for 'snippet editor' do
     stub_feature_flags(snippets_vue: false)
     stub_feature_flags(snippets_edit_vue: false)
     sign_in(user)
-    visit new_snippet_path
   end
 
   def description_field
@@ -28,6 +27,8 @@ shared_examples_for 'snippet editor' do
   end
 
   it 'Authenticated user creates a snippet' do
+    visit new_snippet_path
+
     fill_form
 
     click_button('Create snippet')
@@ -42,6 +43,8 @@ shared_examples_for 'snippet editor' do
   end
 
   it 'previews a snippet with file' do
+    visit new_snippet_path
+
     # Click placeholder first to expand full description field
     description_field.click
     fill_in 'personal_snippet_description', with: 'My Snippet'
@@ -62,6 +65,8 @@ shared_examples_for 'snippet editor' do
   end
 
   it 'uploads a file when dragging into textarea' do
+    visit new_snippet_path
+
     fill_form
 
     dropzone_file Rails.root.join('spec', 'fixtures', 'banana_sample.gif')
@@ -86,6 +91,8 @@ shared_examples_for 'snippet editor' do
         allow(instance).to receive(:create_commit).and_raise(StandardError, error)
       end
 
+      visit new_snippet_path
+
       fill_form
 
       click_button('Create snippet')
@@ -107,6 +114,8 @@ shared_examples_for 'snippet editor' do
   end
 
   it 'validation fails for the first time' do
+    visit new_snippet_path
+
     fill_in 'personal_snippet_title', with: 'My Snippet Title'
     click_button('Create snippet')
 
@@ -132,6 +141,8 @@ shared_examples_for 'snippet editor' do
   end
 
   it 'Authenticated user creates a snippet with + in filename' do
+    visit new_snippet_path
+
     fill_in 'personal_snippet_title', with: 'My Snippet Title'
     page.within('.file-editor') do
       find(:xpath, "//input[@id='personal_snippet_file_name']").set 'snippet+file+name'
@@ -146,6 +157,27 @@ shared_examples_for 'snippet editor' do
     expect(page).to have_content('snippet+file+name')
     expect(page).to have_content('Hello World!')
   end
+
+  context 'when snippets default visibility level is restricted' do
+    before do
+      stub_application_setting(restricted_visibility_levels: [Gitlab::VisibilityLevel::PRIVATE],
+                              default_snippet_visibility: Gitlab::VisibilityLevel::PRIVATE)
+    end
+
+    it 'creates a snippet using the lowest available visibility level as default' do
+      visit new_snippet_path
+
+      fill_form
+
+      click_button('Create snippet')
+      wait_for_requests
+
+      visit snippets_path
+      click_link('Internal')
+
+      expect(page).to have_content('My Snippet Title')
+    end
+  end
 end
 
 describe 'User creates snippet', :js do

spec/helpers/visibility_level_helper_spec.rb

@@ -184,6 +184,84 @@ describe VisibilityLevelHelper do
     end
   end
 
+  shared_examples_for 'available visibility level' do
+    using RSpec::Parameterized::TableSyntax
+
+    let(:user) { create(:user) }
+
+    subject { helper.available_visibility_levels(form_model) }
+
+    public_vis = Gitlab::VisibilityLevel::PUBLIC
+    internal_vis = Gitlab::VisibilityLevel::INTERNAL
+    private_vis = Gitlab::VisibilityLevel::PRIVATE
+
+    where(:restricted_visibility_levels, :expected) do
+      [] | [private_vis, internal_vis, public_vis]
+      [private_vis] | [internal_vis, public_vis]
+      [private_vis, internal_vis] | [public_vis]
+      [private_vis, public_vis] | [internal_vis]
+      [internal_vis] | [private_vis, public_vis]
+      [internal_vis, private_vis] | [public_vis]
+      [internal_vis, public_vis] | [private_vis]
+      [public_vis] | [private_vis, internal_vis]
+      [public_vis, private_vis] | [internal_vis]
+      [public_vis, internal_vis] | [private_vis]
+    end
+
+    before do
+      allow(helper).to receive(:current_user) { user }
+    end
+
+    with_them do
+      before do
+        stub_application_setting(restricted_visibility_levels: restricted_visibility_levels)
+      end
+
+      it { is_expected.to eq(expected) }
+    end
+
+    it 'excludes disallowed visibility levels' do
+      stub_application_setting(restricted_visibility_levels: [])
+      allow(helper).to receive(:disallowed_visibility_level?).with(form_model, private_vis) { true }
+      allow(helper).to receive(:disallowed_visibility_level?).with(form_model, internal_vis) { false }
+      allow(helper).to receive(:disallowed_visibility_level?).with(form_model, public_vis) { false }
+
+      expect(subject).to eq([internal_vis, public_vis])
+    end
+  end
+
+  describe '#available_visibility_levels' do
+    it_behaves_like 'available visibility level' do
+      let(:form_model) { project_snippet }
+    end
+
+    it_behaves_like 'available visibility level' do
+      let(:form_model) { personal_snippet }
+    end
+
+    it_behaves_like 'available visibility level' do
+      let(:form_model) { project }
+    end
+
+    it_behaves_like 'available visibility level' do
+      let(:form_model) { group }
+    end
+  end
+
+  describe '#snippets_selected_visibility_level' do
+    let(:available_levels) { [Gitlab::VisibilityLevel::PUBLIC, Gitlab::VisibilityLevel::INTERNAL] }
+
+    it 'returns the selected visibility level' do
+      expect(helper.snippets_selected_visibility_level(available_levels, Gitlab::VisibilityLevel::PUBLIC))
+        .to eq(Gitlab::VisibilityLevel::PUBLIC)
+    end
+
+    it "fallbacks using the lowest available visibility level when selected level isn't available" do
+      expect(helper.snippets_selected_visibility_level(available_levels, Gitlab::VisibilityLevel::PRIVATE))
+       .to eq(Gitlab::VisibilityLevel::INTERNAL)
+    end
+  end
+
   describe 'multiple_visibility_levels_restricted?' do
     using RSpec::Parameterized::TableSyntax