Streaming tool calls (#29179)

https://github.com/user-attachments/assets/7854a737-ef83-414c-b397-45122e4f32e8



Release Notes:

- Create file and edit file tools now stream their tool descriptions, so
you can see what they're doing sooner.

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>

crates/assistant_tools/src/create_file_tool.rs

@@ -33,8 +33,18 @@ pub struct CreateFileToolInput {
     pub contents: String,
 }
 
+#[derive(Debug, Serialize, Deserialize, JsonSchema)]
+struct PartialInput {
+    #[serde(default)]
+    path: String,
+    #[serde(default)]
+    contents: String,
+}
+
 pub struct CreateFileTool;
 
+const DEFAULT_UI_TEXT: &str = "Create file";
+
 impl Tool for CreateFileTool {
     fn name(&self) -> String {
         "create_file".into()
@@ -62,7 +72,14 @@ impl Tool for CreateFileTool {
                 let path = MarkdownString::inline_code(&input.path);
                 format!("Create file {path}")
             }
-            Err(_) => "Create file".to_string(),
+            Err(_) => DEFAULT_UI_TEXT.to_string(),
+        }
+    }
+
+    fn still_streaming_ui_text(&self, input: &serde_json::Value) -> String {
+        match serde_json::from_value::<PartialInput>(input.clone()).ok() {
+            Some(input) if !input.path.is_empty() => input.path,
+            _ => DEFAULT_UI_TEXT.to_string(),
         }
     }
 
@@ -111,3 +128,60 @@ impl Tool for CreateFileTool {
         .into()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde_json::json;
+
+    #[test]
+    fn still_streaming_ui_text_with_path() {
+        let tool = CreateFileTool;
+        let input = json!({
+            "path": "src/main.rs",
+            "contents": "fn main() {\n    println!(\"Hello, world!\");\n}"
+        });
+
+        assert_eq!(tool.still_streaming_ui_text(&input), "src/main.rs");
+    }
+
+    #[test]
+    fn still_streaming_ui_text_without_path() {
+        let tool = CreateFileTool;
+        let input = json!({
+            "path": "",
+            "contents": "fn main() {\n    println!(\"Hello, world!\");\n}"
+        });
+
+        assert_eq!(tool.still_streaming_ui_text(&input), DEFAULT_UI_TEXT);
+    }
+
+    #[test]
+    fn still_streaming_ui_text_with_null() {
+        let tool = CreateFileTool;
+        let input = serde_json::Value::Null;
+
+        assert_eq!(tool.still_streaming_ui_text(&input), DEFAULT_UI_TEXT);
+    }
+
+    #[test]
+    fn ui_text_with_valid_input() {
+        let tool = CreateFileTool;
+        let input = json!({
+            "path": "src/main.rs",
+            "contents": "fn main() {\n    println!(\"Hello, world!\");\n}"
+        });
+
+        assert_eq!(tool.ui_text(&input), "Create file `src/main.rs`");
+    }
+
+    #[test]
+    fn ui_text_with_invalid_input() {
+        let tool = CreateFileTool;
+        let input = json!({
+            "invalid": "field"
+        });
+
+        assert_eq!(tool.ui_text(&input), DEFAULT_UI_TEXT);
+    }
+}