Don't reuse the Chalk solver

This slows down analysis-stats a bit (~5% in my measurement), but improves
incremental checking a lot because we can reuse trait solve results.

crates/ra_hir/src/db.rs

@@ -18,8 +18,7 @@ pub use hir_ty::db::{
     FieldTypesQuery, GenericDefaultsQuery, GenericPredicatesForParamQuery, GenericPredicatesQuery,
     HirDatabase, HirDatabaseStorage, ImplDatumQuery, ImplSelfTyQuery, ImplTraitQuery,
     ImplsForTraitQuery, ImplsInCrateQuery, InternAssocTyValueQuery, InternChalkImplQuery,
-    InternTypeCtorQuery, StructDatumQuery, TraitDatumQuery, TraitSolveQuery, TraitSolverQuery,
-    TyQuery, ValueTyQuery,
+    InternTypeCtorQuery, StructDatumQuery, TraitDatumQuery, TraitSolveQuery, TyQuery, ValueTyQuery,
 };
 
 #[test]

crates/ra_hir_ty/src/db.rs

@@ -66,14 +66,6 @@ pub trait HirDatabase: DefDatabase {
     #[salsa::invoke(crate::traits::impls_for_trait_query)]
     fn impls_for_trait(&self, krate: CrateId, trait_: TraitId) -> Arc<[ImplId]>;
 
-    /// This provides the Chalk trait solver instance. Because Chalk always
-    /// works from a specific crate, this query is keyed on the crate; and
-    /// because Chalk does its own internal caching, the solver is wrapped in a
-    /// Mutex and the query does an untracked read internally, to make sure the
-    /// cached state is thrown away when input facts change.
-    #[salsa::invoke(crate::traits::trait_solver_query)]
-    fn trait_solver(&self, krate: CrateId) -> crate::traits::TraitSolver;
-
     // Interned IDs for Chalk integration
     #[salsa::interned]
     fn intern_type_ctor(&self, type_ctor: TypeCtor) -> crate::TypeCtorId;

crates/ra_hir_ty/src/traits.rs

@@ -1,12 +1,9 @@
 //! Trait solving using Chalk.
-use std::{
-    panic,
-    sync::{Arc, Mutex},
-};
+use std::{panic, sync::Arc};
 
 use chalk_ir::cast::Cast;
 use hir_def::{expr::ExprId, DefWithBodyId, ImplId, TraitId, TypeAliasId};
-use ra_db::{impl_intern_key, salsa, Canceled, CrateId};
+use ra_db::{impl_intern_key, salsa, CrateId};
 use ra_prof::profile;
 use rustc_hash::FxHashSet;
 
@@ -19,74 +16,6 @@ use self::chalk::{from_chalk, Interner, ToChalk};
 pub(crate) mod chalk;
 mod builtin;
 
-#[derive(Debug, Clone)]
-pub struct TraitSolver {
-    krate: CrateId,
-    inner: Arc<Mutex<chalk_solve::Solver<Interner>>>,
-}
-
-/// We need eq for salsa
-impl PartialEq for TraitSolver {
-    fn eq(&self, other: &TraitSolver) -> bool {
-        Arc::ptr_eq(&self.inner, &other.inner)
-    }
-}
-
-impl Eq for TraitSolver {}
-
-impl TraitSolver {
-    fn solve(
-        &self,
-        db: &impl HirDatabase,
-        goal: &chalk_ir::UCanonical<chalk_ir::InEnvironment<chalk_ir::Goal<Interner>>>,
-    ) -> Option<chalk_solve::Solution<Interner>> {
-        let context = ChalkContext { db, krate: self.krate };
-        log::debug!("solve goal: {:?}", goal);
-        let mut solver = match self.inner.lock() {
-            Ok(it) => it,
-            // Our cancellation works via unwinding, but, as chalk is not
-            // panic-safe, we need to make sure to propagate the cancellation.
-            // Ideally, we should also make chalk panic-safe.
-            Err(_) => ra_db::Canceled::throw(),
-        };
-
-        let fuel = std::cell::Cell::new(CHALK_SOLVER_FUEL);
-
-        let solution = panic::catch_unwind({
-            let solver = panic::AssertUnwindSafe(&mut solver);
-            let context = panic::AssertUnwindSafe(&context);
-            move || {
-                solver.0.solve_limited(context.0, goal, || {
-                    context.0.db.check_canceled();
-                    let remaining = fuel.get();
-                    fuel.set(remaining - 1);
-                    if remaining == 0 {
-                        log::debug!("fuel exhausted");
-                    }
-                    remaining > 0
-                })
-            }
-        });
-
-        let solution = match solution {
-            Ok(it) => it,
-            Err(err) => {
-                if err.downcast_ref::<Canceled>().is_some() {
-                    panic::resume_unwind(err)
-                } else {
-                    log::error!("chalk panicked :-(");
-                    // Reset the solver, as it is not panic-safe.
-                    *solver = create_chalk_solver();
-                    None
-                }
-            }
-        };
-
-        log::debug!("solve({:?}) => {:?}", goal, solution);
-        solution
-    }
-}
-
 /// 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.
@@ -100,16 +29,6 @@ struct ChalkContext<'a, DB> {
     krate: CrateId,
 }
 
-pub(crate) fn trait_solver_query(
-    db: &(impl HirDatabase + salsa::Database),
-    krate: CrateId,
-) -> TraitSolver {
-    db.salsa_runtime().report_untracked_read();
-    // krate parameter is just so we cache a unique solver per crate
-    log::debug!("Creating new solver for crate {:?}", krate);
-    TraitSolver { krate, inner: Arc::new(Mutex::new(create_chalk_solver())) }
-}
-
 fn create_chalk_solver() -> chalk_solve::Solver<Interner> {
     let solver_choice =
         chalk_solve::SolverChoice::SLG { max_size: CHALK_SOLVER_MAX_SIZE, expected_answers: None };
@@ -239,10 +158,35 @@ pub(crate) fn trait_solve_query(
     // We currently don't deal with universes (I think / hope they're not yet
     // relevant for our use cases?)
     let u_canonical = chalk_ir::UCanonical { canonical, universes: 1 };
-    let solution = db.trait_solver(krate).solve(db, &u_canonical);
+    let solution = solve(db, krate, &u_canonical);
     solution.map(|solution| solution_from_chalk(db, solution))
 }
 
+fn solve(
+    db: &impl HirDatabase,
+    krate: CrateId,
+    goal: &chalk_ir::UCanonical<chalk_ir::InEnvironment<chalk_ir::Goal<Interner>>>,
+) -> Option<chalk_solve::Solution<Interner>> {
+    let context = ChalkContext { db, krate };
+    log::debug!("solve goal: {:?}", goal);
+    let mut solver = create_chalk_solver();
+
+    let fuel = std::cell::Cell::new(CHALK_SOLVER_FUEL);
+
+    let solution = solver.solve_limited(&context, goal, || {
+        context.db.check_canceled();
+        let remaining = fuel.get();
+        fuel.set(remaining - 1);
+        if remaining == 0 {
+            log::debug!("fuel exhausted");
+        }
+        remaining > 0
+    });
+
+    log::debug!("solve({:?}) => {:?}", goal, solution);
+    solution
+}
+
 fn solution_from_chalk(
     db: &impl HirDatabase,
     solution: chalk_solve::Solution<Interner>,

crates/ra_ide_db/src/change.rs

@@ -362,7 +362,6 @@ impl RootDatabase {
             hir::db::GenericDefaultsQuery
             hir::db::ImplsInCrateQuery
             hir::db::ImplsForTraitQuery
-            hir::db::TraitSolverQuery
             hir::db::InternTypeCtorQuery
             hir::db::InternChalkImplQuery
             hir::db::InternAssocTyValueQuery