Add tool calling support for Gemini models (#27772)

Release Notes:

- N/A

crates/assistant_tools/src/schema.rs

@@ -0,0 +1,120 @@
+use anyhow::Result;
+use language_model::LanguageModelToolSchemaFormat;
+use schemars::{
+    schema::{RootSchema, Schema, SchemaObject},
+    JsonSchema,
+};
+
+pub fn json_schema_for<T: JsonSchema>(format: LanguageModelToolSchemaFormat) -> serde_json::Value {
+    let schema = root_schema_for::<T>(format);
+    schema_to_json(&schema, format).expect("Failed to convert tool calling schema to JSON")
+}
+
+pub fn schema_to_json(
+    schema: &RootSchema,
+    format: LanguageModelToolSchemaFormat,
+) -> Result<serde_json::Value> {
+    let mut value = serde_json::to_value(schema)?;
+    match format {
+        LanguageModelToolSchemaFormat::JsonSchema => Ok(value),
+        LanguageModelToolSchemaFormat::JsonSchemaSubset => {
+            transform_fields_to_json_schema_subset(&mut value);
+            Ok(value)
+        }
+    }
+}
+
+fn root_schema_for<T: JsonSchema>(format: LanguageModelToolSchemaFormat) -> RootSchema {
+    let mut generator = match format {
+        LanguageModelToolSchemaFormat::JsonSchema => schemars::SchemaGenerator::default(),
+        LanguageModelToolSchemaFormat::JsonSchemaSubset => {
+            schemars::r#gen::SchemaSettings::default()
+                .with(|settings| {
+                    settings.meta_schema = None;
+                    settings.inline_subschemas = true;
+                    settings
+                        .visitors
+                        .push(Box::new(TransformToJsonSchemaSubsetVisitor));
+                })
+                .into_generator()
+        }
+    };
+    generator.root_schema_for::<T>()
+}
+
+#[derive(Debug, Clone)]
+struct TransformToJsonSchemaSubsetVisitor;
+
+impl schemars::visit::Visitor for TransformToJsonSchemaSubsetVisitor {
+    fn visit_root_schema(&mut self, root: &mut RootSchema) {
+        schemars::visit::visit_root_schema(self, root)
+    }
+
+    fn visit_schema(&mut self, schema: &mut Schema) {
+        schemars::visit::visit_schema(self, schema)
+    }
+
+    fn visit_schema_object(&mut self, schema: &mut SchemaObject) {
+        // Ensure that the type field is not an array, this happens when we use
+        // Option<T>, the type will be [T, "null"].
+        if let Some(instance_type) = schema.instance_type.take() {
+            schema.instance_type = match instance_type {
+                schemars::schema::SingleOrVec::Single(t) => {
+                    Some(schemars::schema::SingleOrVec::Single(t))
+                }
+                schemars::schema::SingleOrVec::Vec(items) => items
+                    .into_iter()
+                    .next()
+                    .map(schemars::schema::SingleOrVec::from),
+            };
+        }
+
+        // One of is not supported, use anyOf instead.
+        if let Some(subschema) = schema.subschemas.as_mut() {
+            if let Some(one_of) = subschema.one_of.take() {
+                subschema.any_of = Some(one_of);
+            }
+        }
+
+        schemars::visit::visit_schema_object(self, schema)
+    }
+}
+
+fn transform_fields_to_json_schema_subset(json: &mut serde_json::Value) {
+    if let serde_json::Value::Object(obj) = json {
+        if let Some(default) = obj.get("default") {
+            let is_null = default.is_null();
+            //Default is not supported, so we need to remove it.
+            obj.remove("default");
+            if is_null {
+                obj.insert("nullable".to_string(), serde_json::Value::Bool(true));
+            }
+        }
+
+        // If a type is not specified for an input parameter we need to add it.
+        if obj.contains_key("description")
+            && !obj.contains_key("type")
+            && !(obj.contains_key("anyOf")
+                || obj.contains_key("oneOf")
+                || obj.contains_key("allOf"))
+        {
+            obj.insert(
+                "type".to_string(),
+                serde_json::Value::String("string".to_string()),
+            );
+        }
+
+        //Format field is only partially supported (e.g. not uint compatibility)
+        obj.remove("format");
+
+        for (_, value) in obj.iter_mut() {
+            if let serde_json::Value::Object(_) | serde_json::Value::Array(_) = value {
+                transform_fields_to_json_schema_subset(value);
+            }
+        }
+    } else if let serde_json::Value::Array(arr) = json {
+        for item in arr.iter_mut() {
+            transform_fields_to_json_schema_subset(item);
+        }
+    }
+}