Reduce Chalk max_size parameter, add test for slow case

crates/ra_hir/src/ty/tests.rs

@@ -2581,6 +2581,35 @@ fn test() { foo.call()<|>; }
     );
 }
 
+#[test]
+fn method_resolution_slow() {
+    // this can get quite slow if we set the solver size limit too high
+    let t = type_at(
+        r#"
+//- /main.rs
+trait Send {}
+
+struct S1; impl Send for S1;
+struct S2; impl Send for S2;
+struct U1;
+
+trait Trait { fn method(self); }
+
+struct X1<A, B> {}
+impl<A, B> Send for X1<A, B> where A: Send, B: Send {}
+
+struct S<B, C> {}
+
+trait Fn {}
+
+impl<B, C> Trait for S<B, C> where C: Fn, B: Send {}
+
+fn test() { (S {}).method()<|>; }
+"#,
+    );
+    assert_eq!(t, "{unknown}");
+}
+
 fn type_at_pos(db: &MockDatabase, pos: FilePosition) -> String {
     let file = db.parse(pos.file_id);
     let expr = algo::find_node_at_offset::<ast::Expr>(file.syntax(), pos.offset).unwrap();

crates/ra_hir/src/ty/traits.rs

@@ -14,6 +14,11 @@ mod chalk;
 
 pub(crate) type Solver = chalk_solve::Solver;
 
+/// This controls the maximum size of types Chalk considers. If we set this too
+/// high, we can run into slow edge cases; if we set it too low, Chalk won't
+/// find some solutions.
+const CHALK_SOLVER_MAX_SIZE: usize = 2;
+
 #[derive(Debug, Copy, Clone)]
 struct ChalkContext<'a, DB> {
     db: &'a DB,
@@ -22,7 +27,8 @@ struct ChalkContext<'a, DB> {
 
 pub(crate) fn solver(_db: &impl HirDatabase, _krate: Crate) -> Arc<Mutex<Solver>> {
     // krate parameter is just so we cache a unique solver per crate
-    let solver_choice = chalk_solve::SolverChoice::SLG { max_size: 10 };
+    let solver_choice = chalk_solve::SolverChoice::SLG { max_size: CHALK_SOLVER_MAX_SIZE };
+    debug!("Creating new solver for crate {:?}", _krate);
     Arc::new(Mutex::new(solver_choice.into_solver()))
 }
 
@@ -53,6 +59,7 @@ fn solve(
 ) -> Option<chalk_solve::Solution> {
     let context = ChalkContext { db, krate };
     let solver = db.solver(krate);
+    debug!("solve goal: {:?}", goal);
     let solution = solver.lock().unwrap().solve(&context, goal);
     debug!("solve({:?}) => {:?}", goal, solution);
     solution

crates/ra_hir/src/ty/traits/chalk.rs

@@ -345,11 +345,14 @@ where
             return Vec::new();
         }
         let trait_ = from_chalk(self.db, trait_id);
-        self.db
+        let result: Vec<_> = self
+            .db
             .impls_for_trait(self.krate, trait_)
             .iter()
             .map(|impl_block| impl_block.to_chalk(self.db))
-            .collect()
+            .collect();
+        debug!("impls_for_trait returned {} impls", result.len());
+        result
     }
     fn impl_provided_for(
         &self,