fix: use kill_on_drop() to avoid zombie proc in error case (#887)

In the previous macOS file search implementation, we spawned an mdfind child
process and killed it when we got the results we needed to avoid zombie
processes.  However, this kill step would be skipped if an error happened
during query results processing as we propagate errors.

This commit replaces the manual kill operation with the `ChildProcHandle.kill_on_drop()`
API to let RAII do the job to fix the issue.

Author: SteveLauC

docs/content.en/docs/release-notes/_index.md

@@ -33,6 +33,7 @@ Information about release notes of Coco App is provided here.
 - fix: shortcut key not opening extension store #877
 - fix: set up hotkey on main thread or Windows will complain #879
 - fix: resolve deeplink login issue #881
+- fix: use kill_on_drop() to avoid zombie proc in error case #887
 
 ### ✈️ Improvements
 

src-tauri/src/extension/built_in/file_search/implementation/macos.rs

@@ -25,7 +25,7 @@ pub(crate) async fn hits(
     size: usize,
     config: &FileSearchConfig,
 ) -> Result<Vec<(Document, f64)>, String> {
-    let (mut iter, mut mdfind_child_process) =
+    let (mut iter, _mdfind_child_process) =
         execute_mdfind_query(&query_string, from, size, &config)?;
 
     // Convert results to documents
@@ -73,12 +73,6 @@ pub(crate) async fn hits(
 
         hits.push((doc, SCORE));
     }
-    // Kill the mdfind process once we get the needed results to prevent zombie
-    // processes.
-    mdfind_child_process
-        .kill()
-        .await
-        .map_err(|e| format!("{:?}", e))?;
 
     Ok(hits)
 }
@@ -130,8 +124,9 @@ fn build_mdfind_query(query_string: &str, config: &FileSearchConfig) -> Vec<Stri
 /// # Return value:
 ///
 /// * impl Stream: an async iterator that will yield the matched files
-/// * Child: The handle to the mdfind process, we need to kill it once we
-///   collect all the results to avoid zombie processes.
+/// * Child: The handle to the mdfind process.  The child process will be killed
+///   when this handle gets dropped, we need to keep it alive until we exhaust
+///   all the query results.
 fn execute_mdfind_query(
     query_string: &str,
     from: usize,
@@ -149,6 +144,7 @@ fn execute_mdfind_query(
         .args(&args[1..])
         .stdout(tx)
         .stderr(std::process::Stdio::null())
+        .kill_on_drop(true)
         .spawn()
         .map_err(|e| format!("Failed to spawn mdfind: {}", e))?;
     let config_clone = config.clone();