[ty] Parallelize workspace symbols

This is a pretty naive approach, but it makes cold times for listing
workspace symbols in home-assistant under 1s on my machine.

Courtesy of Micha:
https://github.com/astral-sh/ruff/pull/20030#discussion_r2292924171

Cargo.lock

@@ -4243,6 +4243,7 @@ dependencies = [
  "bitflags 2.9.2",
  "insta",
  "itertools 0.14.0",
+ "rayon",
  "regex",
  "ruff_db",
  "ruff_memory_usage",

crates/ty_ide/Cargo.toml

@@ -23,6 +23,7 @@ ty_python_semantic = { workspace = true }
 ty_project = { workspace = true, features = ["testing"] }
 
 itertools = { workspace = true }
+rayon = { workspace = true }
 regex = { workspace = true }
 rustc-hash = { workspace = true }
 salsa = { workspace = true, features = ["compact_str"] }

crates/ty_ide/src/workspace_symbols.rs

@@ -10,7 +10,6 @@ pub fn workspace_symbols(db: &dyn Db, query: &str) -> Vec<WorkspaceSymbolInfo> {
         return Vec::new();
     }
 
-    let mut results = Vec::new();
     let project = db.project();
 
     let options = SymbolsOptions {
@@ -19,22 +18,34 @@ pub fn workspace_symbols(db: &dyn Db, query: &str) -> Vec<WorkspaceSymbolInfo> {
         query_string: Some(query.into()),
     };
 
-    // Get all files in the project
     let files = project.files(db);
+    let results = std::sync::Mutex::new(Vec::new());
+    {
+        let db = db.dyn_clone();
+        let files = &files;
+        let options = &options;
+        let results = &results;
 
+        rayon::scope(move |s| {
             // For each file, extract symbols and add them to results
             for file in files.iter() {
-        let file_symbols = symbols_for_file(db, *file, &options);
+                let db = db.dyn_clone();
-
+                s.spawn(move |_| {
-        for symbol in file_symbols {
+                    for symbol in symbols_for_file(&*db, *file, options) {
-            results.push(WorkspaceSymbolInfo {
+                        // It seems like we could do better here than
+                        // locking `results` for every single symbol,
+                        // but this works pretty well as it is.
+                        results.lock().unwrap().push(WorkspaceSymbolInfo {
                             symbol: symbol.clone(),
                             file: *file,
                         });
                     }
+                });
+            }
+        });
     }
 
-    results
+    results.into_inner().unwrap()
 }
 
 /// A symbol found in the workspace, including the file it was found in.