docs(firebaseai): document tool combinations in Tool.functionDeclarations

[Yusufihsangorgel]

Description

Adds a note to the Tool.functionDeclarations docs about combining function declarations with other tools such as Google Search. In #17687, a request with both through FirebaseAI.googleAI() failed with Tool use with function calling is unsupported. The note says that some models reject such a request and that this can change with new model versions, without listing models. It suggests separate requests as a workaround. The Tool.googleSearch docs now point to the note.

A comment on #18192 asked for more detail in the functionDeclarations docs instead of validating the combination on the client. Only doc comments in lib/src/tool.dart change.

Checked in packages/firebase_ai/firebase_ai with dart format, dart analyze lib test --fatal-infos and flutter test. I did not run melos or call the live API. The firebase_ai e2e jobs need repository secrets and do not run on forks.

Related Issues

• Fixes [firebase_ai]: Grounding with Google not working in Flutter #17687

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