Add InvocationRequired property to FunctionCallContent #7126

Copilot · 2025-12-10T16:12:59Z

Implementation Summary

Successfully implemented the InvocationRequired property for FunctionCallContent with the following features:

Goals Achieved

This implementation enables:

IChatClients to produce FunctionCallContent/FunctionResultContent that should not be re-invoked by callers
Callers to distinguish whether a FunctionCallContent is informative or requires processing
Multiple FunctionInvokingChatClients in a pipeline without duplicating work
Proper serialization and deserialization of function call state

Original prompt

Add a get/set InvocationRequired property to FunctionCallContent. It should default to true and then be set to false by FunctionInvokingChatClient when the associated AIFunction has been processed and a FunctionResultContent created. It should be ignored by JSON serialization when it has its default value of false. Please ensure great test coverage in existing tests, validating the property is set appropriately, and add new tests to ensure that FunctionCallContent will InvocationRequired=false are ignored by FunctionInvokingChatClient; it shouldn't see them as content to be processed.

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src/Libraries/Microsoft.Extensions.AI/ChatCompletion/FunctionInvokingChatClient.cs

stephentoub · 2025-12-10T19:29:17Z

@copilot, fix the CI failures

Copilot · 2025-12-10T19:55:40Z

@copilot, fix the CI failures

Fixed in da8a275. The tests were reusing FunctionCallContent objects across multiple test iterations. When we set InvocationRequired=false during processing, subsequent iterations saw them as already processed. Added a ResetPlanFunctionCallStates helper method that resets InvocationRequired=true at the beginning of test helper methods. All 385 AI tests and 1115 abstraction tests now pass.

stephentoub · 2025-12-10T20:00:30Z

@javiercn, @jozkee, @westey-m, thoughts on this approach?

The goal here is to:

Enable an IChatClient to produce FunctionCallContent / FunctionResultContent that should not be re-invoked by callers.
Allow callers to distinguish whether an FCC is informative or a request. Today when a consumer gets back an FCC they don't know if it's been handled, and need to look for a corresponding FRC to determine whether it should be handled or not.
Allow multiple FunctionInvocationChatClients to be in a pipeline and not duplicate work.
Maybe allow FunctionCallContent / FunctionResultContent (or derivations to represent server-side invocations).

Copilot

Pull request overview

This PR adds an InvocationRequired property to FunctionCallContent to prevent duplicate processing of function calls in the FunctionInvokingChatClient. The property defaults to true and is set to false after a function call has been processed, allowing the middleware to distinguish between new function calls and already-processed ones. This is particularly useful in scenarios where chat history containing function calls is reused across multiple requests.

Key changes:

Added InvocationRequired boolean property to FunctionCallContent with JSON serialization support (omitted when false)
Modified FunctionInvokingChatClient to set the property to false after processing and filter out function calls with InvocationRequired = false
Added comprehensive test coverage including unit tests for serialization behavior and integration tests for filtering logic

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/FunctionCallContent.cs	Adds `InvocationRequired` property with field initializer defaulting to `true`, marked as experimental, with `JsonIgnoreCondition.WhenWritingDefault` to omit when false
src/Libraries/Microsoft.Extensions.AI/ChatCompletion/FunctionInvokingChatClient.cs	Updates `CopyFunctionCalls` to filter out function calls where `InvocationRequired = false` and sets the property to false in `ProcessFunctionCallAsync` and `CreateFunctionResultContent`
test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Contents/FunctionCallContentTests.cs	Adds 6 unit tests covering property defaults, getters/setters, and JSON serialization/deserialization behavior
test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/FunctionInvokingChatClientTests.cs	Adds 4 integration tests for the filtering behavior and a `ResetPlanFunctionCallStates` helper method to reset the property when reusing test plans across multiple invocations

src/Libraries/Microsoft.Extensions.AI/ChatCompletion/FunctionInvokingChatClient.cs

src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/FunctionCallContent.cs

src/Libraries/Microsoft.Extensions.AI/ChatCompletion/FunctionInvokingChatClient.cs

test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/FunctionInvokingChatClientTests.cs

src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/FunctionCallContent.cs

Copilot · 2025-12-10T22:58:04Z

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rogerbarreto · 2025-12-12T11:24:14Z

Assuming we will always have a FRC for invoked FCC even for server-side invoked FCCs.

The representation of a function that was already invoked already exists as the FRC, I understand the need for it but I'm not sure if this should be represented as an extra serializeable boolean in the FCC with not specific pointer/hint.

I suggest that we might just have a nullable [JsonIgnore] Result property pointing to what is the FRC for that FCC when it was already invoked.

Further downstream FICC could check if the FCC has a FRC as to know if it was invoked, this makes some API usage more intuitive as well.

Often I found myself having to store the FCC.Id to map what was the FRC.CallId, this would make some calling code easier to handle.

javiercn · 2025-12-12T16:18:21Z

@javiercn, @jozkee, @westey-m, thoughts on this approach?

The goal here is to:

Enable an IChatClient to produce FunctionCallContent / FunctionResultContent that should not be re-invoked by callers.

Allow callers to distinguish whether an FCC is informative or a request. Today when a consumer gets back an FCC they don't know if it's been handled, and need to look for a corresponding FRC to determine whether it should be handled or not.

Allow multiple FunctionInvocationChatClients to be in a pipeline and not duplicate work.

Maybe allow FunctionCallContent / FunctionResultContent (or derivations to represent server-side invocations).

Could we instead look for the matching FunctionResultContent on the stream? If we see a function -> result pair on the response we can consider it as handled, couldn't we?

I think this goes in line with what @rogerbarreto has in mind.

jozkee · 2025-12-12T16:30:06Z

@javiercn does AGUI always returns a matching FRC for a server-side function?
cc @mattleibow which had a similar use case.

stephentoub · 2025-12-12T16:33:29Z

Could we instead look for the matching FunctionResultContent on the stream? If we see a function -> result pair on the response we can consider it as handled, couldn't we?

We could, it's just fairly complex, especially in a streaming scenario where you may have received the FCC but not yet the FRC, but even in non-streaming they can (and typically) are spread across multiple messages. We would need to employ that logic in FunctionInvokingChatClient, and any consumer that wanted to handle function invocation manually (often for a subset of requests) would need to have similar logic (we could try to expose something in a helper?) We would also need to mandate that any FCC that should be considered handled must always have a paired FRC.

I'd tried this approach in #7011 but gave up on it due to complexity. We can experiment with it again, though.

stephentoub · 2025-12-12T21:34:44Z

#7141 is an attempt at handling it based on looking for corresponding FRCs in FunctionInvokingChatClient.

mattleibow · 2026-01-13T19:25:22Z

I created this issue to see if we could use that in links in code and docs around this issue, but also have a central place to get comments/discussions that are not directly related to a specific PR. #7204

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

src/Libraries/Microsoft.Extensions.AI.Abstractions/Microsoft.Extensions.AI.Abstractions.json

src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/FunctionCallContent.cs

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Copilot AI changed the title ~~[WIP] Add get/set InvocationRequired property to FunctionCallContent~~ Add InvocationRequired property to FunctionCallContent Dec 10, 2025

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stephentoub mentioned this pull request Dec 12, 2025

Add content to represent service-side actions #7109

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stephentoub added * NO MERGE * Do not merge this PR as long as this label is present. area-ai Microsoft.Extensions.AI libraries labels Dec 12, 2025

stephentoub closed this Dec 15, 2025

mattleibow mentioned this pull request Jan 13, 2026

FunctionInvokingChatClient should not re-invoke already-handled FunctionCallContent #7204

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Copilot AI mentioned this pull request Jan 21, 2026

Add InvocationRequired to FunctionCallContent; make MCP types inherit from base content types #7220

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jozkee mentioned this pull request Jan 21, 2026

Ignore FunctionCallContent with paired FunctionResultContent in FunctionInvokingChatClient #7141

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stephentoub removed the * NO MERGE * Do not merge this PR as long as this label is present. label Jan 23, 2026

stephentoub reopened this Jan 23, 2026

Copilot AI and others added 2 commits January 23, 2026 16:06

Initial plan

69b996b

Add InvocationRequired property to FunctionCallContent with tests

30d0ee7

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

stephentoub approved these changes Jan 23, 2026

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stephentoub requested a review from jozkee January 23, 2026 21:20

stephentoub force-pushed the copilot/add-invocation-required-property branch from 6f38322 to 30d0ee7 Compare January 23, 2026 22:05

Add InvocationRequired property to FunctionCallContent #7126

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Microsoft Reviewers: Open in CodeFlow

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