fix(gitlab-ci-config): allow strings in the 'include' keyword

This fix is a followup to !24098 which introduced a validation of the
`include:` keyword of a gitlab-ci configuration file when triggered
from /ci/lint API calls.

However, there was a test case missing: the case of a single string as
value. I have added a test case for that which shows that the code was
not validating it correctly.

This commit fixes that to allow all `include:` valid inputs.

2 files changed, 9 insertions, 1 deletions

diff --git a/lib/gitlab/ci/config/entry/includes.rb b/lib/gitlab/ci/config/entry/includes.rb
index 82b2b1ccf4b..43e74dfd628 100644
--- a/lib/gitlab/ci/config/entry/includes.rb
+++ b/lib/gitlab/ci/config/entry/includes.rb
@@ -11,7 +11,7 @@ module Gitlab
           include ::Gitlab::Config::Entry::Validatable
 
           validations do
-            validates :config, type: Array
+            validates :config, array_or_string: true
           end
 
           def self.aspects
diff --git a/lib/gitlab/config/entry/validators.rb b/lib/gitlab/config/entry/validators.rb
index 746fe83f90f..df34d254c65 100644
--- a/lib/gitlab/config/entry/validators.rb
+++ b/lib/gitlab/config/entry/validators.rb
@@ -54,6 +54,14 @@ module Gitlab
           end
         end
 
+        class ArrayOrStringValidator < ActiveModel::EachValidator
+          def validate_each(record, attribute, value)
+            unless value.is_a?(Array) || value.is_a?(String)
+              record.errors.add(attribute, 'should be an array or a string')
+            end
+          end
+        end
+
         class BooleanValidator < ActiveModel::EachValidator
           include LegacyValidationHelpers