IntEnum tool parameters produce an invalid function declaration: integer values in a STRING enum

[MarcHuang168]

🔴 Required Information

Describe the Bug:
When a tool function has a parameter annotated with an enum.IntEnum, the generated function declaration sets type: STRING but fills enum with the raw integer values (e.g. [1, 2]). google.genai.types.Schema.enum is typed list[str], so the declaration is invalid by the SDK's own contract: building the same schema through the constructor raises a ValidationError, and serializing the ADK-built one emits PydanticSerializationUnexpectedValue warnings. The invalid value only gets through because the parser assigns schema.enum = [...] after construction, which bypasses validation.

Steps to Reproduce:

1. pip install google-adk
2. Run the snippet under Minimal Reproduction Code
3. Observe the emitted schema and the serializer warnings

Expected Behavior:
The declaration is valid for types.Schema — e.g. the enum values are strings (["1", "2"], or the member names), consistent with type: STRING.

Observed Behavior:

UserWarning: Pydantic serializer warnings:
  PydanticSerializationUnexpectedValue(Expected `str` - serialized value may not be as expected [field_name='enum', input_value=1, input_type=int])
  PydanticSerializationUnexpectedValue(Expected `str` - serialized value may not be as expected [field_name='enum', input_value=2, input_type=int])
ADK emits: {'enum': [1, 2], 'type': <Type.STRING: 'STRING'>}
types.Schema rejects it: ValidationError

Environment Details:

• ADK Library Version (pip show google-adk): 2.8.0
• Desktop OS: macOS (arm64)
• Python Version (python -V): 3.14.7

Model Information:

• Are you using LiteLLM: No
• Which model is being used: N/A (reproduces at declaration-build time, no model call needed)

---

🟡 Optional Information

Regression:
Unknown.

Logs:
See Observed Behavior above.

Screenshots / Video:
N/A

Additional Context:
str-valued enums work correctly; only non-string enum values are affected. The relevant code is the Enum branch in _function_parameter_parse_util._parse_schema_from_parameter (schema.enum = [e.value for e in param.annotation]).

I'd be happy to submit a PR for this. Since it involves a choice (stringify the values vs. use member names, and how the argument is mapped back to the enum on the call path), I'd appreciate guidance on the preferred approach before opening one, per the contributing guide. Reported with AI assistance; reproduced and reviewed by me.

Minimal Reproduction Code:

import enum
from google.genai import types
from google.adk.tools._automatic_function_calling_util import from_function_with_options


class Level(enum.IntEnum):
    LOW = 1
    HIGH = 2


def set_level(level: Level) -> str:
    """Set the level.

    Args:
        level: the level to set
    """
    return "ok"


decl = from_function_with_options(set_level)
print("ADK emits:", decl.parameters.properties["level"].model_dump(exclude_none=True))

# The same schema is rejected when built through the public constructor
try:
    types.Schema(type="STRING", enum=[1, 2])
except Exception as e:
    print("types.Schema rejects it:", type(e).__name__)

How often has this issue occurred?:

• Always (100%)

[maxx1958]

I've been there.
If only a number is entered in the HITL situation
What I expect is string, but int is entered, error occurs. 100%

[chelsealong]

Picking this one up now — opening a PR shortly. Flagging it here so nobody duplicates the work; if someone is already on it, say so and I will drop mine.

[surajksharma07]

@MarcHuang168 chelsealong already has a fix up in #6981 that stringifies the enum values before they hit the schema so the STRING/enum pair stays valid. Could you pull that branch and confirm it clears things on your end? No need for a separate PR just want your sign-off before it will go for review.

[MarcHuang168]

@surajksharma07 Confirmed — pulled #6981 (33c3853) and re-ran the reproduction from this issue on my end: the declaration now emits {'enum': ['1', '2'], 'type': STRING} with no serializer warnings. Looks good to me.