Tool calling fails with 'Duplicate function declaration found'

[sharpomatic]

Environment details

• Programming language: C#
• OS: Win11
• Language runtime version: .NET 10
• Package version: 0.13.1

Steps to reproduce

1. Take you example code from the README for tool calling. Like this.

using Google.GenAI;
using Microsoft.Extensions.AI;
using System.ComponentModel

// assuming credentials are set up in environment variables as instructed above.
IChatClient chatClient = new Client().AsIChatClient("gemini-2.0-flash")
    .AsBuilder()
    .UseFunctionInvocation()
    .UseOpenTelemetry()
    .Build();

ChatOptions options = new()
{
    Tools = [AIFunctionFactory.Create(([Description("The name of the person whose age is to be retrieved")] string personName) => personName switch
    {
        "Alice" => 30,
        "Bob" => 25,
        _ => 35
    }, "get_person_age", "Gets the age of the specified person");
};

await foreach (var update in chatClient.GetStreamingResponseAsync("How much older is Alice than Bob?", options))
{
    Console.Write(update);
}

2. Modify the ChatOptions so it has a GenerateContentConfig instance.

var generateContentConfig = new Google.GenAI.Types.GenerateContentConfig();

ChatOptions options = new()
{
    RawRepresentationFactory = (_) => generateContentConfig,
    Tools = [AIFunctionFactory.Create(([Description("The name of the person whose age is to be retrieved")] string personName) => personName switch
    {
        "Alice" => 30,
        "Bob" => 25,
        _ => 35
    }, "get_person_age", "Gets the age of the specified person");
};

Having the RawRepresentationFactory will cause the tool calling to now fail with an error of 'Duplicate function declaration found:'. Remove that entry in ChatOptions and it works again.

[shivvaam0001]

Hi @sharpomatic
Thank you for bringing this to our attention. We truly appreciate you flagging this issue, we will file a bug internally.

[yyyu-google]

@stephentoub Could you have a look at this? Thank you

[stephentoub]

var generateContentConfig = new Google.GenAI.Types.GenerateContentConfig();
ChatOptions options = new()
{
RawRepresentationFactory = (_) => generateContentConfig,

This part of the repro is buggy. Each call to RawRepresentationFactory should construct a new instance, because it's going to be mutated by the IChatClient. It should instead create and configure the config in the delegate, e.g.

RawRepresentationFactory = (_) =>  new Google.GenAI.Types.GenerateContentConfig();

The docs for RawRepresentationFactory call this out:
https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.ai.chatoptions.rawrepresentationfactory
"Such implementations might mutate the supplied options instance further based on other settings supplied on this ChatOptions instance or from other inputs, like the enumerable of ChatMessages. Therefore, it is strongly recommended to not return shared instances and instead make the callback return a new instance on each call."