Support Array Type for Tool Calling Function

[sayanshaw24]

Summary

Fixes a crash in ConvertParameters when a tool function property's "type" field is a JSON array (e.g. ["string", "null"]) instead of a plain string.

Per the OpenAI function calling spec, strict mode requires all fields to be marked as required, and optional fields are denoted by adding "null" as a type option — resulting in "type": ["string", "null"] rather than "type": "string".

Previously, ConvertParameters unconditionally did std::string type = prop_schema["type"], which throws json.exception.type_error.302 when the value is an array. This caused a 500 error in downstream consumers like Foundry Local.

Changes

shared/api/chat_template.cc

• Updated ConvertParameters to handle "type" as:
  • string — normalized as before ("string" → "str", others as-is)
  • array — extracts the first non-"null" type from the array and normalizes it
  • any other JSON value — passed through as-is (safety net for unexpected schemas)

test/pp_api_test/test_tokenizer_chat.cc

• Added Qwen2_5_ChatTemplateWithOAIFunctionTypeArrayType test that uses "type": ["string", "null"] on a property, verifying it normalizes correctly without crashing.

Validation

• Validated unit test in ORT Extensions
• Tested e2e with ORT GenAI using phi-4 mini and deepseek r1 distill qwen-1.5b

Fixes

• Foundry local doesn't support array for "type" property in tools Foundry-Local#576