eval: Do not create run files for skipped examples (#28800)

Release Notes:

- N/A

crates/eval/src/eval.rs

@@ -199,7 +199,7 @@ fn main() {
 
             future::join_all(clone_tasks).await;
 
-            for example in examples.iter() {
+            for example in examples.iter_mut() {
                 example.setup().await?;
             }
 

crates/eval/src/example.rs

@@ -57,7 +57,7 @@ pub struct Example {
     /// Content of `criteria.md`
     pub criteria: String,
     /// Markdown output file to append to
-    pub output_file: Arc<Mutex<File>>,
+    pub output_file: Option<Arc<Mutex<File>>>,
     /// Path to markdown output file
     pub output_file_path: PathBuf,
     /// Prefix used for logging that identifies this example
@@ -97,14 +97,13 @@ impl Example {
             "{}.md",
             dir_path.file_name().unwrap().to_str().unwrap()
         ));
-        let output_file = Arc::new(Mutex::new(File::create(&output_file_path).unwrap()));
 
         Ok(Example {
             name: name.clone(),
             base: toml::from_str(&fs::read_to_string(&base_path)?)?,
             prompt: fs::read_to_string(prompt_path.clone())?,
             criteria: fs::read_to_string(criteria_path.clone())?,
-            output_file,
+            output_file: None,
             output_file_path,
             log_prefix: name,
         })
@@ -132,7 +131,7 @@ impl Example {
     }
 
     /// Set up the example by checking out the specified Git revision
-    pub async fn setup(&self) -> Result<()> {
+    pub async fn setup(&mut self) -> Result<()> {
         let repo_path = repo_path_for_url(&self.base.url);
 
         println!("{}Fetching", self.log_prefix);
@@ -171,9 +170,20 @@ impl Example {
             .await?;
         }
 
+        // Create the output file
+        let output_file = Arc::new(Mutex::new(File::create(&self.output_file_path)?));
+        self.output_file = Some(output_file);
+
         Ok(())
     }
 
+    /// Returns the output file, panicking if it's not set
+    fn output_file(&self) -> Arc<Mutex<File>> {
+        self.output_file
+            .clone()
+            .expect("Output file not created. Call setup() first.")
+    }
+
     pub fn run(
         &self,
         model: Arc<dyn LanguageModel>,
@@ -287,7 +297,8 @@ impl Example {
                 thread_store.update(cx, |thread_store, cx| thread_store.create_thread(cx))?;
 
             {
-                let mut output_file = this.output_file.lock().unwrap();
+                let output_file_ref = this.output_file();
+                let mut output_file = output_file_ref.lock().unwrap();
                 writeln!(&mut output_file, "👤 USER:").log_err();
                 writeln!(&mut output_file, "{}", this.prompt).log_err();
                 writeln!(&mut output_file, "🤖 ASSISTANT:").log_err();
@@ -304,7 +315,8 @@ impl Example {
             });
 
             let event_handler_task = cx.spawn({
-                let output_file = this.output_file.clone();
+                // Need to clone the Arc here because the reference from output_file() won't live long enough
+                let output_file = this.output_file.clone().unwrap();
                 let log_prefix = this.log_prefix.clone();
                 let tool_use_counts = tool_use_counts.clone();
                 let thread = thread.downgrade();
@@ -471,7 +483,8 @@ impl Example {
 
         let response = send_language_model_request(model, request, cx).await?;
 
-        let mut output_file = self.output_file.lock().unwrap();
+        let output_file_ref = self.output_file();
+        let mut output_file = output_file_ref.lock().unwrap();
 
         writeln!(&mut output_file, "\n\n").log_err();
         writeln!(&mut output_file, "========================================").log_err();