fix: schema generation (#862)

Author: ms-jpq

lib/openai/helpers/structured_output/union_of.rb

@@ -21,6 +21,7 @@ class UnionOf
         #
         # @return [Hash{Symbol=>Object}]
         def to_json_schema_inner(state:)
+          # rubocop:disable Metrics/BlockLength
           OpenAI::Helpers::StructuredOutput::JsonSchemaConverter.cache_def!(state, type: self) do
             path = state.fetch(:path)
             mergeable_keys = {[:anyOf] => 0, [:type] => 0}
@@ -33,7 +34,9 @@ def to_json_schema_inner(state:)
             end
 
             schemas.each do |schema|
-              mergeable_keys.each_key { mergeable_keys[_1] += 1 if schema.keys == _1 }
+              mergeable_keys.each_key do
+                mergeable_keys[_1] += 1 if schema.keys == _1 && schema[_1].is_a?(Array)
+              end
             end
             mergeable = mergeable_keys.any? { _1.last == schemas.length }
             if mergeable
@@ -48,6 +51,7 @@ def to_json_schema_inner(state:)
               }
             end
           end
+          # rubocop:enable Metrics/BlockLength
         end
 
         private_class_method :new

test/openai/helpers/structured_output_test.rb

@@ -39,6 +39,7 @@ class M3 < OpenAI::Helpers::StructuredOutput::BaseModel
   U1 = OpenAI::Helpers::StructuredOutput::UnionOf[Integer, A1]
   U2 = OpenAI::Helpers::StructuredOutput::UnionOf[M2, M3]
   U3 = OpenAI::Helpers::StructuredOutput::UnionOf[A1, A1]
+  U4 = OpenAI::Helpers::StructuredOutput::UnionOf[String, NilClass]
 
   def test_coerce
     cases = {
@@ -117,6 +118,12 @@ def test_to_schema
             additionalProperties: false
           }
         ]
+      },
+      U4 => {
+        anyOf: [
+          {type: "string"},
+          {type: "null"}
+        ]
       }
     }
     cases.each do |input, expected|