Rework obligation handling

We can't do the easy hack that we did before anymore, where we kept
track of whether any inference variables changed since the last time we
rechecked obligations. Instead, we store the obligations in
canonicalized form; that way we can easily check the inference variables
to see whether they have changed since the goal was canonicalized.

1 files changed, 35 insertions, 13 deletions

diff --git a/crates/hir_ty/src/method_resolution.rs b/crates/hir_ty/src/method_resolution.rs
index 37e1f89d8..08e385a42 100644
--- a/crates/hir_ty/src/method_resolution.rs
+++ b/crates/hir_ty/src/method_resolution.rs
@@ -577,6 +577,7 @@ fn iterate_method_candidates_by_receiver(
         if iterate_inherent_methods(
             self_ty,
             db,
+            env.clone(),
             name,
             Some(receiver_ty),
             krate,
@@ -613,8 +614,16 @@ fn iterate_method_candidates_for_self_ty(
     name: Option<&Name>,
     mut callback: &mut dyn FnMut(&Ty, AssocItemId) -> bool,
 ) -> bool {
-    if iterate_inherent_methods(self_ty, db, name, None, krate, visible_from_module, &mut callback)
-    {
+    if iterate_inherent_methods(
+        self_ty,
+        db,
+        env.clone(),
+        name,
+        None,
+        krate,
+        visible_from_module,
+        &mut callback,
+    ) {
         return true;
     }
     iterate_trait_method_candidates(self_ty, db, env, krate, traits_in_scope, name, None, callback)
@@ -653,12 +662,12 @@ fn iterate_trait_method_candidates(
         for (_name, item) in data.items.iter() {
             // Don't pass a `visible_from_module` down to `is_valid_candidate`,
             // since only inherent methods should be included into visibility checking.
-            if !is_valid_candidate(db, name, receiver_ty, *item, self_ty, None) {
+            if !is_valid_candidate(db, env.clone(), name, receiver_ty, *item, self_ty, None) {
                 continue;
             }
             if !known_implemented {
                 let goal = generic_implements_goal(db, env.clone(), t, self_ty.clone());
-                if db.trait_solve(krate, goal).is_none() {
+                if db.trait_solve(krate, goal.cast(&Interner)).is_none() {
                     continue 'traits;
                 }
             }
@@ -675,6 +684,7 @@ fn iterate_trait_method_candidates(
 fn iterate_inherent_methods(
     self_ty: &Canonical<Ty>,
     db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
     name: Option<&Name>,
     receiver_ty: Option<&Canonical<Ty>>,
     krate: CrateId,
@@ -690,14 +700,24 @@ fn iterate_inherent_methods(
 
         for &impl_def in impls.for_self_ty(&self_ty.value) {
             for &item in db.impl_data(impl_def).items.iter() {
-                if !is_valid_candidate(db, name, receiver_ty, item, self_ty, visible_from_module) {
+                if !is_valid_candidate(
+                    db,
+                    env.clone(),
+                    name,
+                    receiver_ty,
+                    item,
+                    self_ty,
+                    visible_from_module,
+                ) {
                     continue;
                 }
                 // we have to check whether the self type unifies with the type
                 // that the impl is for. If we have a receiver type, this
                 // already happens in `is_valid_candidate` above; if not, we
                 // check it here
-                if receiver_ty.is_none() && inherent_impl_substs(db, impl_def, self_ty).is_none() {
+                if receiver_ty.is_none()
+                    && inherent_impl_substs(db, env.clone(), impl_def, self_ty).is_none()
+                {
                     cov_mark::hit!(impl_self_type_match_without_receiver);
                     continue;
                 }
@@ -722,7 +742,7 @@ pub fn resolve_indexing_op(
     let deref_chain = autoderef_method_receiver(db, krate, ty);
     for ty in deref_chain {
         let goal = generic_implements_goal(db, env.clone(), index_trait, ty.clone());
-        if db.trait_solve(krate, goal).is_some() {
+        if db.trait_solve(krate, goal.cast(&Interner)).is_some() {
             return Some(ty);
         }
     }
@@ -731,6 +751,7 @@ pub fn resolve_indexing_op(
 
 fn is_valid_candidate(
     db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
     name: Option<&Name>,
     receiver_ty: Option<&Canonical<Ty>>,
     item: AssocItemId,
@@ -749,7 +770,7 @@ fn is_valid_candidate(
                 if !data.has_self_param() {
                     return false;
                 }
-                let transformed_receiver_ty = match transform_receiver_ty(db, m, self_ty) {
+                let transformed_receiver_ty = match transform_receiver_ty(db, env, m, self_ty) {
                     Some(ty) => ty,
                     None => return false,
                 };
@@ -776,6 +797,7 @@ fn is_valid_candidate(
 
 pub(crate) fn inherent_impl_substs(
     db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
     impl_id: ImplId,
     self_ty: &Canonical<Ty>,
 ) -> Option<Substitution> {
@@ -798,8 +820,7 @@ pub(crate) fn inherent_impl_substs(
         binders: CanonicalVarKinds::from_iter(&Interner, kinds),
         value: (self_ty_with_vars, self_ty.value.clone()),
     };
-    let trait_env = Arc::new(TraitEnvironment::default()); // FIXME
-    let substs = super::infer::unify(db, trait_env, &tys)?;
+    let substs = super::infer::unify(db, env, &tys)?;
     // We only want the substs for the vars we added, not the ones from self_ty.
     // Also, if any of the vars we added are still in there, we replace them by
     // Unknown. I think this can only really happen if self_ty contained
@@ -824,6 +845,7 @@ fn fallback_bound_vars(s: Substitution, num_vars_to_keep: usize) -> Substitution
 
 fn transform_receiver_ty(
     db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
     function_id: FunctionId,
     self_ty: &Canonical<Ty>,
 ) -> Option<Ty> {
@@ -833,7 +855,7 @@ fn transform_receiver_ty(
             .fill_with_unknown()
             .build(),
         AssocContainerId::ImplId(impl_id) => {
-            let impl_substs = inherent_impl_substs(db, impl_id, &self_ty)?;
+            let impl_substs = inherent_impl_substs(db, env, impl_id, &self_ty)?;
             TyBuilder::subst_for_def(db, function_id)
                 .use_parent_substs(&impl_substs)
                 .fill_with_unknown()
@@ -853,7 +875,7 @@ pub fn implements_trait(
     trait_: TraitId,
 ) -> bool {
     let goal = generic_implements_goal(db, env, trait_, ty.clone());
-    let solution = db.trait_solve(krate, goal);
+    let solution = db.trait_solve(krate, goal.cast(&Interner));
 
     solution.is_some()
 }
@@ -866,7 +888,7 @@ pub fn implements_trait_unique(
     trait_: TraitId,
 ) -> bool {
     let goal = generic_implements_goal(db, env, trait_, ty.clone());
-    let solution = db.trait_solve(krate, goal);
+    let solution = db.trait_solve(krate, goal.cast(&Interner));
 
     matches!(solution, Some(crate::Solution::Unique(_)))
 }