Fix: VariantCollectionCoercer#to_s returns "Array[Type, ...]" notation

CHANGELOG.md

@@ -66,6 +66,7 @@
 * [#2678](https://github.com/ruby-grape/grape/pull/2678): Update rubocop to 1.86.0 and autocorrect offenses - [@ericproulx](https://github.com/ericproulx).
 * [#2682](https://github.com/ruby-grape/grape/pull/2682): Fix `Style/OptionalBooleanParameter` offenses - [@ericproulx](https://github.com/ericproulx).
 * [#2699](https://github.com/ruby-grape/grape/pull/2699): Fix `Grape::Validations::Types::CustomTypeCoercer` dropping symbolized hash keys for `Array`/`Set` types; refactor the class for readability - [@ericproulx](https://github.com/ericproulx).
+* [#2758](https://github.com/ruby-grape/grape/pull/2758): Fix `VariantCollectionCoercer#to_s` to return `"Array[Type, ...]"` notation instead of a raw object string - [@bogdan](https://github.com/bogdan).
 * [#2700](https://github.com/ruby-grape/grape/pull/2700): Fix README typos, remove obsolete Ruby 2.4 / Fixnum section, and replace incorrect `requires + values + allow_blank` note with a correct one covering `optional + values` semantics (closes #2631) - [@ericproulx](https://github.com/ericproulx).
 * [#2703](https://github.com/ruby-grape/grape/pull/2703): Catch exceptions raised inside `rescue_from` blocks; new `rescue_from :internal_grape_exceptions` opt-in for unrecognised internal errors (resolves [#2482](https://github.com/ruby-grape/grape/issues/2482)) - [@ericproulx](https://github.com/ericproulx).
 * [#2706](https://github.com/ruby-grape/grape/pull/2706): Fix `optional :foo, message: 'oops'` raising `UnknownValidator` - [@ericproulx](https://github.com/ericproulx).

lib/grape/validations/types/variant_collection_coercer.rb

@@ -26,6 +26,14 @@ def initialize(types, method = nil)
           @member_coercer = MultipleTypeCoercer.new types, method
         end
 
+        # Returns the Grape DSL notation for this coercer, e.g. "Array[Integer, String]".
+        # Distinct from the plain-array string "[Integer, String]" produced by the
+        # +types:+ keyword, which lets documentation tools tell the two apart.
+        def to_s
+          container = @types.is_a?(Set) ? 'Set' : 'Array'
+          "#{container}[#{@types.join(', ')}]"
+        end
+
         # Coerce the given value.
         #
         # @param value [Array<String>] collection of values to be coerced

spec/grape/endpoint/declared_spec.rb

@@ -40,6 +40,7 @@
         optional :empty_hash_two, type: Hash
         optional :empty_set, type: Set
         optional :empty_typed_set, type: Set[String]
+        optional :empty_variant_set, type: Set[Integer, String]
       end
     end
 
@@ -108,7 +109,7 @@
       end
       get '/declared?first=present'
       expect(last_response).to be_successful
-      expect(JSON.parse(last_response.body).keys.size).to eq(12)
+      expect(JSON.parse(last_response.body).keys.size).to eq(13)
     end
 
     it 'has a optional param with default value all the time' do
@@ -205,6 +206,14 @@
         expect(body['nested']['empty_typed_set']).to eq(json_empty_set)
       end
 
+      it 'sets objects with type=Set[Integer, String] (variant collection) to be a set' do
+        get '/declared?first=present'
+        expect(last_response).to be_successful
+
+        body = JSON.parse(last_response.body)
+        expect(body['empty_variant_set']).to eq(JSON.parse(Set.new.to_json))
+      end
+
       it 'sets objects with type=Array to be an array' do
         get '/declared?first=present'
         expect(last_response).to be_successful

spec/grape/validations/validations_spec_spec.rb

@@ -36,12 +36,21 @@
     it 'wraps a multiple type from :type in a VariantCollectionCoercer' do
       multi_spec = described_class.from(type: [Integer, String])
       expect(multi_spec.coerce_type).to be_a(Grape::Validations::Types::VariantCollectionCoercer)
+      expect(multi_spec.coerce_type.to_s).to eq('Array[Integer, String]')
+      expect(multi_spec.coerce_method).to be_nil
+    end
+
+    it 'wraps a Set multiple type from :type in a VariantCollectionCoercer' do
+      multi_spec = described_class.from(type: Set[Integer, String])
+      expect(multi_spec.coerce_type).to be_a(Grape::Validations::Types::VariantCollectionCoercer)
+      expect(multi_spec.coerce_type.to_s).to eq('Set[Integer, String]')
       expect(multi_spec.coerce_method).to be_nil
     end
 
     it 'extracts :types as a plain coerce list' do
       spec = described_class.from(types: [Integer, String])
       expect(spec.coerce_type).to eq([Integer, String])
+      expect(spec.coerce_type.to_s).to eq('[Integer, String]')
     end
   end