Return nil license if Gitaly is down

When exploring projects (/explore, /explore/projects/starred,
/explore/projects/trending), a small license icon is displayed for "MIT", "GNU,"
etc. That license requires a Gitaly call, so if Gitaly is unreachable or down,
the entire page will return a 503. This MR should return nil, or an empty
license so that the page doesn't require it in order to load.

app/helpers/projects_helper.rb

@@ -381,6 +381,14 @@ module ProjectsHelper
     @project.grafana_integration&.enabled?
   end
 
+  def project_license_name(project)
+    project.repository.license&.name
+  rescue GRPC::Unavailable, GRPC::DeadlineExceeded, Gitlab::Git::CommandError => e
+    Gitlab::ErrorTracking.track_exception(e)
+
+    nil
+  end
+
   private
 
   def get_project_nav_tabs(project, current_user)

app/views/shared/projects/_project.html.haml

@@ -14,6 +14,7 @@
 - updated_tooltip = time_ago_with_tooltip(project.last_activity_date)
 - css_controls_class = compact_mode ? [] : ["flex-lg-row", "justify-content-lg-between"]
 - avatar_container_class = project.creator && use_creator_avatar ? '' : 'rect-avatar'
+- license_name = project_license_name(project)
 
 %li.project-row.d-flex{ class: css_class }
   = cache(cache_key) do
@@ -40,10 +41,10 @@
           %span.metadata-info.visibility-icon.append-right-10.prepend-top-8.text-secondary.has-tooltip{ data: { container: 'body', placement: 'top' }, title: visibility_icon_description(project) }
             = visibility_level_icon(project.visibility_level, fw: true)
 
-          - if explore_projects_tab? && project.repository.license
+          - if explore_projects_tab? && license_name
             %span.metadata-info.d-inline-flex.align-items-center.append-right-10.prepend-top-8
               = sprite_icon('scale', size: 14, css_class: 'append-right-4')
-              = project.repository.license.name
+              = license_name
 
           - if !explore_projects_tab? && access&.nonzero?
             -# haml-lint:disable UnnecessaryStringOutput

changelogs/unreleased/199442-explore-projects.yml

+---
+title: Handle Gitaly failure when fetching license
+merge_request: 24310
+author:
+type: fixed

spec/helpers/projects_helper_spec.rb

@@ -994,4 +994,56 @@ describe ProjectsHelper do
       it { is_expected.to eq(grafana_integration.enabled) }
     end
   end
+
+  describe '#project_license_name(project)' do
+    let_it_be(:project) { create(:project) }
+    let_it_be(:repository) { project.repository }
+
+    subject { project_license_name(project) }
+
+    context 'gitaly is working appropriately' do
+      it 'returns the license name' do
+        license = Licensee::License.new('mit')
+        allow(repository).to receive(:license).and_return(license)
+
+        expect(subject).to eq(license.name)
+      end
+    end
+
+    context 'gitaly is unreachable' do
+      shared_examples 'returns nil and tracks exception' do
+        it { is_expected.to be_nil }
+
+        it 'tracks the exception' do
+          expect(Gitlab::ErrorTracking).to receive(:track_exception).with(
+            an_instance_of(exception)
+          )
+
+          subject
+        end
+      end
+
+      before do
+        allow(repository).to receive(:license).and_raise(exception)
+      end
+
+      context "Gitlab::Git::CommandError" do
+        let(:exception) { Gitlab::Git::CommandError }
+
+        it_behaves_like 'returns nil and tracks exception'
+      end
+
+      context "GRPC::Unavailable" do
+        let(:exception) { GRPC::Unavailable }
+
+        it_behaves_like 'returns nil and tracks exception'
+      end
+
+      context "GRPC::DeadlineExceeded" do
+        let(:exception) { GRPC::DeadlineExceeded }
+
+        it_behaves_like 'returns nil and tracks exception'
+      end
+    end
+  end
 end