[ty] Gracefully handle salsa cancellations and panics in background request handlers

crates/ruff_benchmark/benches/ty.rs

@@ -131,7 +131,7 @@ fn benchmark_incremental(criterion: &mut Criterion) {
     fn setup() -> Case {
         let case = setup_tomllib_case();
 
-        let result: Vec<_> = case.db.check().unwrap();
+        let result: Vec<_> = case.db.check();
 
         assert_diagnostics(&case.db, &result, EXPECTED_TOMLLIB_DIAGNOSTICS);
 
@@ -159,7 +159,7 @@ fn benchmark_incremental(criterion: &mut Criterion) {
             None,
         );
 
-        let result = db.check().unwrap();
+        let result = db.check();
 
         assert_eq!(result.len(), EXPECTED_TOMLLIB_DIAGNOSTICS.len());
     }
@@ -179,7 +179,7 @@ fn benchmark_cold(criterion: &mut Criterion) {
             setup_tomllib_case,
             |case| {
                 let Case { db, .. } = case;
-                let result: Vec<_> = db.check().unwrap();
+                let result: Vec<_> = db.check();
 
                 assert_diagnostics(db, &result, EXPECTED_TOMLLIB_DIAGNOSTICS);
             },
@@ -293,7 +293,7 @@ fn benchmark_many_string_assignments(criterion: &mut Criterion) {
             },
             |case| {
                 let Case { db, .. } = case;
-                let result = db.check().unwrap();
+                let result = db.check();
                 assert_eq!(result.len(), 0);
             },
             BatchSize::SmallInput,
@@ -339,7 +339,7 @@ fn benchmark_many_tuple_assignments(criterion: &mut Criterion) {
             },
             |case| {
                 let Case { db, .. } = case;
-                let result = db.check().unwrap();
+                let result = db.check();
                 assert_eq!(result.len(), 0);
             },
             BatchSize::SmallInput,

crates/ruff_db/src/panic.rs

@@ -1,3 +1,4 @@
+use std::any::Any;
 use std::backtrace::BacktraceStatus;
 use std::cell::Cell;
 use std::panic::Location;
@@ -24,17 +25,25 @@ impl Payload {
             None
         }
     }
+
+    pub fn downcast_ref<R: Any>(&self) -> Option<&R> {
+        self.0.downcast_ref::<R>()
+    }
 }
 
 impl std::fmt::Display for PanicError {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        writeln!(f, "panicked at")?;
+        write!(f, "panicked at")?;
         if let Some(location) = &self.location {
             write!(f, " {location}")?;
         }
         if let Some(payload) = self.payload.as_str() {
             write!(f, ":\n{payload}")?;
         }
+        if let Some(query_trace) = self.salsa_backtrace.as_ref() {
+            let _ = writeln!(f, "{query_trace}");
+        }
+
         if let Some(backtrace) = &self.backtrace {
             match backtrace.status() {
                 BacktraceStatus::Disabled => {
@@ -49,6 +58,7 @@ impl std::fmt::Display for PanicError {
                 _ => {}
             }
         }
+
         Ok(())
     }
 }

crates/ty/src/lib.rs

@@ -243,12 +243,14 @@ impl MainLoop {
                 MainLoopMessage::CheckWorkspace => {
                     let db = db.clone();
                     let sender = self.sender.clone();
-                    let mut reporter = R::default();
 
                     // Spawn a new task that checks the project. This needs to be done in a separate thread
                     // to prevent blocking the main loop here.
                     rayon::spawn(move || {
-                        match db.check_with_reporter(&mut reporter) {
+                        match salsa::Cancelled::catch(|| {
+                            let mut reporter = R::default();
+                            db.check_with_reporter(&mut reporter)
+                        }) {
                             Ok(result) => {
                                 // Send the result back to the main loop for printing.
                                 sender

crates/ty/tests/file_watching.rs

@@ -1135,7 +1135,7 @@ print(sys.last_exc, os.getegid())
         Ok(())
     })?;
 
-    let diagnostics = case.db.check().context("Failed to check project.")?;
+    let diagnostics = case.db.check();
 
     assert_eq!(diagnostics.len(), 2);
     assert_eq!(
@@ -1160,7 +1160,7 @@ print(sys.last_exc, os.getegid())
     })
     .expect("Search path settings to be valid");
 
-    let diagnostics = case.db.check().context("Failed to check project.")?;
+    let diagnostics = case.db.check();
     assert!(diagnostics.is_empty());
 
     Ok(())
@@ -1763,10 +1763,7 @@ fn changes_to_user_configuration() -> anyhow::Result<()> {
     let foo = case
         .system_file(case.project_path("foo.py"))
         .expect("foo.py to exist");
-    let diagnostics = case
-        .db()
-        .check_file(foo)
-        .context("Failed to check project.")?;
+    let diagnostics = case.db().check_file(foo);
 
     assert!(
         diagnostics.is_empty(),
@@ -1786,10 +1783,7 @@ fn changes_to_user_configuration() -> anyhow::Result<()> {
 
     case.apply_changes(changes);
 
-    let diagnostics = case
-        .db()
-        .check_file(foo)
-        .context("Failed to check project.")?;
+    let diagnostics = case.db().check_file(foo);
 
     assert!(
         diagnostics.len() == 1,

crates/ty_project/src/db.rs

@@ -8,8 +8,8 @@ use ruff_db::files::{File, Files};
 use ruff_db::system::System;
 use ruff_db::vendored::VendoredFileSystem;
 use ruff_db::{Db as SourceDb, Upcast};
+use salsa::Event;
 use salsa::plumbing::ZalsaDatabase;
-use salsa::{Cancelled, Event};
 use ty_ide::Db as IdeDb;
 use ty_python_semantic::lint::{LintRegistry, RuleSelection};
 use ty_python_semantic::{Db as SemanticDb, Program};
@@ -76,24 +76,21 @@ impl ProjectDatabase {
     }
 
     /// Checks all open files in the project and its dependencies.
-    pub fn check(&self) -> Result<Vec<Diagnostic>, Cancelled> {
+    pub fn check(&self) -> Vec<Diagnostic> {
         let mut reporter = DummyReporter;
         let reporter = AssertUnwindSafe(&mut reporter as &mut dyn Reporter);
-        self.with_db(|db| db.project().check(db, reporter))
+        self.project().check(self, reporter)
     }
 
     /// Checks all open files in the project and its dependencies, using the given reporter.
-    pub fn check_with_reporter(
-        &self,
-        reporter: &mut dyn Reporter,
-    ) -> Result<Vec<Diagnostic>, Cancelled> {
+    pub fn check_with_reporter(&self, reporter: &mut dyn Reporter) -> Vec<Diagnostic> {
         let reporter = AssertUnwindSafe(reporter);
-        self.with_db(|db| db.project().check(db, reporter))
+        self.project().check(self, reporter)
     }
 
     #[tracing::instrument(level = "debug", skip(self))]
-    pub fn check_file(&self, file: File) -> Result<Vec<Diagnostic>, Cancelled> {
-        self.with_db(|db| self.project().check_file(db, file))
+    pub fn check_file(&self, file: File) -> Vec<Diagnostic> {
+        self.project().check_file(self, file)
     }
 
     /// Returns a mutable reference to the system.
@@ -107,13 +104,6 @@ impl ProjectDatabase {
         Arc::get_mut(&mut self.system)
             .expect("ref count should be 1 because `zalsa_mut` drops all other DB references.")
     }
-
-    pub(crate) fn with_db<F, T>(&self, f: F) -> Result<T, Cancelled>
-    where
-        F: FnOnce(&ProjectDatabase) -> T + std::panic::UnwindSafe,
-    {
-        Cancelled::catch(|| f(self))
-    }
 }
 
 impl Upcast<dyn SemanticDb> for ProjectDatabase {

crates/ty_server/src/server.rs

@@ -1,10 +1,5 @@
 //! Scheduling, I/O, and API endpoints.
 
-use std::num::NonZeroUsize;
-// The new PanicInfoHook name requires MSRV >= 1.82
-#[expect(deprecated)]
-use std::panic::PanicInfo;
-
 use lsp_server::Message;
 use lsp_types::{
     ClientCapabilities, DiagnosticOptions, DiagnosticServerCapabilities,
@@ -13,6 +8,8 @@ use lsp_types::{
     TextDocumentSyncCapability, TextDocumentSyncKind, TextDocumentSyncOptions,
     TypeDefinitionProviderCapability, Url,
 };
+use std::num::NonZeroUsize;
+use std::panic::PanicHookInfo;
 
 use self::connection::{Connection, ConnectionInitializer};
 use self::schedule::event_loop_thread;
@@ -125,9 +122,7 @@ impl Server {
     }
 
     pub(crate) fn run(self) -> crate::Result<()> {
-        // The new PanicInfoHook name requires MSRV >= 1.82
-        #[expect(deprecated)]
-        type PanicHook = Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send>;
+        type PanicHook = Box<dyn Fn(&PanicHookInfo<'_>) + 'static + Sync + Send>;
         struct RestorePanicHook {
             hook: Option<PanicHook>,
         }