Validate connection section in direct upload config

For some reason, `Settingslogic` doesn't always provide the right error
message when the `connection` block is omitted. Sometimes it erroneously
attributes the error section to a different part of the YAML
(e.g. `backup`, `dependency_proxy`).

This commit adds on more information on which `connection` block is
missing from the `gitlab.yml` (e.g. LFS, artifacts, or uploads).

Closes https://gitlab.com/gitlab-org/gitlab/issues/38258

changelogs/unreleased/sh-validate-direct-upload-config.yml

+---
+title: Validate connection section in direct upload config
+merge_request: 21270
+author:
+type: fixed

config/initializers/direct_upload_support.rb

@@ -3,17 +3,35 @@ class DirectUploadsValidator
 
   ValidationError = Class.new(StandardError)
 
-  def verify!(object_store)
+  def verify!(uploader_type, object_store)
     return unless object_store.enabled
     return unless object_store.direct_upload
-    return if SUPPORTED_DIRECT_UPLOAD_PROVIDERS.include?(object_store.connection&.provider.to_s)
 
-    raise ValidationError, "Only #{SUPPORTED_DIRECT_UPLOAD_PROVIDERS.join(',')} are supported as a object storage provider when 'direct_upload' is used"
+    raise ValidationError, "Object storage is configured for '#{uploader_type}', but the 'connection' section is missing" unless object_store.key?('connection')
+
+    provider = object_store.connection&.provider.to_s
+
+    raise ValidationError, "No provider configured for '#{uploader_type}'. #{supported_provider_text}" if provider.blank?
+
+    return if SUPPORTED_DIRECT_UPLOAD_PROVIDERS.include?(provider)
+
+    raise ValidationError, "Object storage provider '#{provider}' is not supported " \
+                           "when 'direct_upload' is used for '#{uploader_type}'. #{supported_provider_text}"
+  end
+
+  def supported_provider_text
+    "Only #{SUPPORTED_DIRECT_UPLOAD_PROVIDERS.join(', ')} are supported."
   end
 end
 
 DirectUploadsValidator.new.tap do |validator|
-  [Gitlab.config.artifacts, Gitlab.config.uploads, Gitlab.config.lfs].each do |uploader|
-    validator.verify!(uploader.object_store)
+  CONFIGS = {
+    artifacts: Gitlab.config.artifacts,
+    uploads: Gitlab.config.uploads,
+    lfs: Gitlab.config.lfs
+  }.freeze
+
+  CONFIGS.each do |uploader_type, uploader|
+    validator.verify!(uploader_type, uploader.object_store)
   end
 end

spec/initializers/direct_upload_support_spec.rb

@@ -56,7 +56,7 @@ describe 'Direct upload support' do
           let(:connection) { nil }
 
           it 'raises an error' do
-            expect { subject }.to raise_error /are supported as a object storage provider when 'direct_upload' is used/
+            expect { subject }.to raise_error "No provider configured for '#{config_name}'. Only Google, AWS are supported."
           end
         end
 
@@ -64,7 +64,20 @@ describe 'Direct upload support' do
           let(:provider) { 'Rackspace' }
 
           it 'raises an error' do
-            expect { subject }.to raise_error /are supported as a object storage provider when 'direct_upload' is used/
+            expect { subject }.to raise_error /Object storage provider '#{provider}' is not supported when 'direct_upload' is used for '#{config_name}'/
+          end
+        end
+
+        context 'when connection is omitted' do
+          let(:object_store) do
+            {
+              enabled: enabled,
+              direct_upload: direct_upload
+            }
+          end
+
+          it 'raises an error' do
+            expect { subject }.to raise_error /the 'connection' section is missing/
           end
         end
       end