Normalize legacy function_call finish reason on the Chat path

[PratikDhanave (PratikDhanave)]

Some OpenAI-compatible endpoints still emit the deprecated "function_call" finish reason. The Chat path assigned choice.FinishReason / chunk.Choices[0].FinishReason verbatim, so a caller hitting such an endpoint saw FinishReason == "function_call" where the Python and .NET clients report "tool_calls".

The Python client normalizes this on both parse paths: finish_reason = "tool_calls" if choice.finish_reason == "function_call" else choice.finish_reason.

Change

• Add normalizeChatFinishReason and apply it at both the non-streaming and streaming finish-reason assignment sites. Only "function_call" is remapped; all other reasons pass through unchanged.

This is distinct from the already-implemented Responses-path tool_calls synthesis — this remaps a legacy finish-reason string on the Chat path.

Test

• TestChatLegacyFunctionCallFinishReasonNormalized: a canned completion with "finish_reason":"function_call" now yields FinishReason == "tool_calls". Fails before the change ("function_call"), passes after.

[Copilot]

🟡 Changes recommended

Add regression coverage for the streaming Chat path.

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Pull request overview

Normalizes legacy Chat finish reasons from function_call to tool_calls for compatibility across response paths.

Changes:

• Added shared finish-reason normalization.
• Applied it to streaming and non-streaming Chat responses.
• Added non-streaming regression coverage.

File summaries

File	Summary
provider/openaiprovider/chat.go	Normalizes legacy finish reasons on both Chat paths.
provider/openaiprovider/chat_test.go	Tests non-streaming normalization; streaming coverage is still requested.

Review note (nit, 3 votes): Add streaming regression coverage for function_call normalization.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

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[github-actions]

Scope: user-visible behavior (internal implementation, no exported API change)
Changed Go contract: provider/openaiprovider/chat.go — unexported normalizeChatFinishReason helper now remaps the legacy "function_call" finish reason to "tool_calls" at both the non-streaming and streaming Chat-path assignment sites. No exported types, functions, or signatures changed.
Upstream evidence reviewed: python/packages/openai/agent_framework_openai/_chat_completion_client.py lines 873-877 and 908-920 — finish_reason = "tool_calls" if choice.finish_reason == "function_call" else choice.finish_reason, applied identically on both the non-streaming and streaming parse paths. No equivalent .NET code found in dotnet/src/ (the reference .NET OpenAI chat client relies on Microsoft.Extensions.AI, which is outside this upstream repo).
Result: aligned — the Go change is a faithful, one-to-one port of the Python normalization (same trigger value, same replacement value, same two call sites). No parity issues found.

Generated by Go API Consistency Review Agent · copilot · auto · 23.5 AIC · ⌖ 5.66 AIC · ⊞ 9.2K · ◷