Add tool calling support for Gemini models (#27772)

Release Notes:

- N/A

crates/language_model/src/language_model.rs

@@ -66,6 +66,15 @@ pub enum LanguageModelCompletionEvent {
     UsageUpdate(TokenUsage),
 }
 
+/// Indicates the format used to define the input schema for a language model tool.
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum LanguageModelToolSchemaFormat {
+    /// A JSON schema, see https://json-schema.org
+    JsonSchema,
+    /// A subset of an OpenAPI 3.0 schema object supported by Google AI, see https://ai.google.dev/api/caching#Schema
+    JsonSchemaSubset,
+}
+
 #[derive(Debug, PartialEq, Clone, Copy, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum StopReason {
@@ -176,6 +185,10 @@ pub trait LanguageModel: Send + Sync {
         LanguageModelAvailability::Public
     }
 
+    fn tool_input_format(&self) -> LanguageModelToolSchemaFormat {
+        LanguageModelToolSchemaFormat::JsonSchema
+    }
+
     fn max_token_count(&self) -> usize;
     fn max_output_tokens(&self) -> Option<u32> {
         None

crates/language_model/src/request.rs

@@ -167,6 +167,7 @@ impl LanguageModelImage {
 #[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq, Hash)]
 pub struct LanguageModelToolResult {
     pub tool_use_id: LanguageModelToolUseId,
+    pub tool_name: Arc<str>,
     pub is_error: bool,
     pub content: Arc<str>,
 }