8 files changed, 56 insertions, 88 deletions

diff --git a/crates/hir_ty/src/infer.rs b/crates/hir_ty/src/infer.rs
index 8cfc84b86..ab742e203 100644
--- a/crates/hir_ty/src/infer.rs
+++ b/crates/hir_ty/src/infer.rs
@@ -273,7 +273,7 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn err_ty(&self) -> Ty {
-        TyKind::Error.intern(&Interner)
+        self.result.standard_types.unknown.clone()
     }
 
     fn resolve_all(mut self) -> InferenceResult {
@@ -284,12 +284,14 @@ impl<'a> InferenceContext<'a> {
         self.table.propagate_diverging_flag();
         let mut result = std::mem::take(&mut self.result);
         for ty in result.type_of_expr.values_mut() {
-            let resolved = self.table.resolve_ty_completely(ty.clone());
-            *ty = resolved;
+            *ty = self.table.resolve_ty_completely(ty.clone());
         }
         for ty in result.type_of_pat.values_mut() {
-            let resolved = self.table.resolve_ty_completely(ty.clone());
-            *ty = resolved;
+            *ty = self.table.resolve_ty_completely(ty.clone());
+        }
+        for mismatch in result.type_mismatches.values_mut() {
+            mismatch.expected = self.table.resolve_ty_completely(mismatch.expected.clone());
+            mismatch.actual = self.table.resolve_ty_completely(mismatch.actual.clone());
         }
         result
     }
@@ -343,6 +345,14 @@ impl<'a> InferenceContext<'a> {
     fn insert_type_vars_shallow(&mut self, ty: Ty) -> Ty {
         match ty.kind(&Interner) {
             TyKind::Error => self.table.new_type_var(),
+            TyKind::InferenceVar(..) => {
+                let ty_resolved = self.resolve_ty_shallow(&ty);
+                if ty_resolved.is_unknown() {
+                    self.table.new_type_var()
+                } else {
+                    ty
+                }
+            }
             _ => ty,
         }
     }
@@ -371,18 +381,8 @@ impl<'a> InferenceContext<'a> {
         self.table.unify_inner(ty1, ty2)
     }
 
-    // FIXME get rid of this, instead resolve shallowly where necessary
-    /// Resolves the type as far as currently possible, replacing type variables
-    /// by their known types. All types returned by the infer_* functions should
-    /// be resolved as far as possible, i.e. contain no type variables with
-    /// known type.
-    fn resolve_ty_as_possible(&mut self, ty: Ty) -> Ty {
-        self.resolve_obligations_as_possible();
-
-        self.table.resolve_ty_as_possible(ty)
-    }
-
     fn resolve_ty_shallow(&mut self, ty: &Ty) -> Ty {
+        self.resolve_obligations_as_possible();
         self.table.resolve_ty_shallow(ty)
     }
 
@@ -416,7 +416,7 @@ impl<'a> InferenceContext<'a> {
                 };
                 self.push_obligation(trait_ref.cast(&Interner));
                 self.push_obligation(alias_eq.cast(&Interner));
-                self.resolve_ty_as_possible(ty)
+                ty
             }
             None => self.err_ty(),
         }
diff --git a/crates/hir_ty/src/infer/coerce.rs b/crates/hir_ty/src/infer/coerce.rs
index c85c088f7..00b2b585f 100644
--- a/crates/hir_ty/src/infer/coerce.rs
+++ b/crates/hir_ty/src/infer/coerce.rs
@@ -19,12 +19,12 @@ impl<'a> InferenceContext<'a> {
     /// Unify two types, but may coerce the first one to the second one
     /// using "implicit coercion rules" if needed.
     pub(super) fn coerce(&mut self, from_ty: &Ty, to_ty: &Ty) -> bool {
+        let from_ty = self.resolve_ty_shallow(from_ty);
+        let to_ty = self.resolve_ty_shallow(to_ty);
         // TODO handle expectations properly
         if to_ty.is_unknown() {
             return true;
         }
-        let from_ty = self.resolve_ty_shallow(from_ty);
-        let to_ty = self.resolve_ty_shallow(to_ty);
         match self.coerce_inner(from_ty, &to_ty) {
             Ok(_result) => {
                 // TODO deal with goals
diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 6eaccd9b4..f5782ab24 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -35,7 +35,7 @@ use super::{
 impl<'a> InferenceContext<'a> {
     pub(super) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
         let ty = self.infer_expr_inner(tgt_expr, expected);
-        if ty.is_never() {
+        if self.resolve_ty_shallow(&ty).is_never() {
             // Any expression that produces a value of type `!` must have diverged
             self.diverges = Diverges::Always;
         }
@@ -46,7 +46,7 @@ impl<'a> InferenceContext<'a> {
                 TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() },
             );
         }
-        self.resolve_ty_as_possible(ty)
+        ty
     }
 
     /// Infer type of expression with possibly implicit coerce to the expected type.
@@ -67,7 +67,7 @@ impl<'a> InferenceContext<'a> {
             expected.ty.clone()
         };
 
-        self.resolve_ty_as_possible(ty)
+        ty
     }
 
     fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
@@ -284,8 +284,7 @@ impl<'a> InferenceContext<'a> {
 
                 // Now go through the argument patterns
                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
-                    let resolved = self.resolve_ty_as_possible(arg_ty);
-                    self.infer_pat(*arg_pat, &resolved, BindingMode::default());
+                    self.infer_pat(*arg_pat, &arg_ty, BindingMode::default());
                 }
 
                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
@@ -525,14 +524,14 @@ impl<'a> InferenceContext<'a> {
             Expr::Ref { expr, rawness, mutability } => {
                 let mutability = lower_to_chalk_mutability(*mutability);
                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) =
-                    &expected.ty.as_reference_or_ptr()
+                    &self.resolve_ty_shallow(&expected.ty).as_reference_or_ptr()
                 {
                     if *exp_mutability == Mutability::Mut && mutability == Mutability::Not {
-                        // FIXME: throw type error - expected mut reference but found shared ref,
+                        // FIXME: record type error - expected mut reference but found shared ref,
                         // which cannot be coerced
                     }
                     if *exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
-                        // FIXME: throw type error - expected reference but found ptr,
+                        // FIXME: record type error - expected reference but found ptr,
                         // which cannot be coerced
                     }
                     Expectation::rvalue_hint(Ty::clone(exp_inner))
@@ -559,6 +558,7 @@ impl<'a> InferenceContext<'a> {
             }
             Expr::UnaryOp { expr, op } => {
                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
+                let inner_ty = self.resolve_ty_shallow(&inner_ty);
                 match op {
                     UnaryOp::Deref => match self.resolver.krate() {
                         Some(krate) => {
@@ -615,8 +615,10 @@ impl<'a> InferenceContext<'a> {
                         _ => Expectation::none(),
                     };
                     let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
+                    let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
                     let rhs_expectation = op::binary_op_rhs_expectation(*op, lhs_ty.clone());
                     let rhs_ty = self.infer_expr(*rhs, &Expectation::has_type(rhs_expectation));
+                    let rhs_ty = self.resolve_ty_shallow(&rhs_ty);
 
                     let ret = op::binary_op_return_ty(*op, lhs_ty.clone(), rhs_ty.clone());
 
@@ -699,7 +701,7 @@ impl<'a> InferenceContext<'a> {
                 }
             }
             Expr::Tuple { exprs } => {
-                let mut tys = match expected.ty.kind(&Interner) {
+                let mut tys = match self.resolve_ty_shallow(&expected.ty).kind(&Interner) {
                     TyKind::Tuple(_, substs) => substs
                         .iter(&Interner)
                         .map(|a| a.assert_ty_ref(&Interner).clone())
@@ -716,7 +718,7 @@ impl<'a> InferenceContext<'a> {
                 TyKind::Tuple(tys.len(), Substitution::from_iter(&Interner, tys)).intern(&Interner)
             }
             Expr::Array(array) => {
-                let elem_ty = match expected.ty.kind(&Interner) {
+                let elem_ty = match self.resolve_ty_shallow(&expected.ty).kind(&Interner) {
                     TyKind::Array(st, _) | TyKind::Slice(st) => st.clone(),
                     _ => self.table.new_type_var(),
                 };
@@ -788,7 +790,6 @@ impl<'a> InferenceContext<'a> {
         };
         // use a new type variable if we got unknown here
         let ty = self.insert_type_vars_shallow(ty);
-        let ty = self.resolve_ty_as_possible(ty);
         self.write_expr_ty(tgt_expr, ty.clone());
         ty
     }
@@ -816,7 +817,6 @@ impl<'a> InferenceContext<'a> {
                         }
                     }
 
-                    let ty = self.resolve_ty_as_possible(ty);
                     self.infer_pat(*pat, &ty, BindingMode::default());
                 }
                 Statement::Expr { expr, .. } => {
@@ -894,7 +894,8 @@ impl<'a> InferenceContext<'a> {
         };
         // Apply autoref so the below unification works correctly
         // FIXME: return correct autorefs from lookup_method
-        let actual_receiver_ty = match expected_receiver_ty.as_reference() {
+        let actual_receiver_ty = match self.resolve_ty_shallow(&expected_receiver_ty).as_reference()
+        {
             Some((_, lifetime, mutability)) => {
                 TyKind::Ref(mutability, lifetime, derefed_receiver_ty).intern(&Interner)
             }
@@ -974,6 +975,7 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
+        let callable_ty = self.resolve_ty_shallow(&callable_ty);
         if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(&Interner) {
             let def: CallableDefId = from_chalk(self.db, *fn_def);
             let generic_predicates = self.db.generic_predicates(def.into());
diff --git a/crates/hir_ty/src/infer/pat.rs b/crates/hir_ty/src/infer/pat.rs
index b15f4977d..9c8e3b6ae 100644
--- a/crates/hir_ty/src/infer/pat.rs
+++ b/crates/hir_ty/src/infer/pat.rs
@@ -94,14 +94,15 @@ impl<'a> InferenceContext<'a> {
     pub(super) fn infer_pat(
         &mut self,
         pat: PatId,
-        mut expected: &Ty,
+        expected: &Ty,
         mut default_bm: BindingMode,
     ) -> Ty {
         let body = Arc::clone(&self.body); // avoid borrow checker problem
+        let mut expected = self.resolve_ty_shallow(expected);
 
         if is_non_ref_pat(&body, pat) {
             while let Some((inner, _lifetime, mutability)) = expected.as_reference() {
-                expected = inner;
+                expected = self.resolve_ty_shallow(inner);
                 default_bm = match default_bm {
                     BindingMode::Move => BindingMode::Ref(mutability),
                     BindingMode::Ref(Mutability::Not) => BindingMode::Ref(Mutability::Not),
@@ -147,9 +148,9 @@ impl<'a> InferenceContext<'a> {
             }
             Pat::Or(ref pats) => {
                 if let Some((first_pat, rest)) = pats.split_first() {
-                    let ty = self.infer_pat(*first_pat, expected, default_bm);
+                    let ty = self.infer_pat(*first_pat, &expected, default_bm);
                     for pat in rest {
-                        self.infer_pat(*pat, expected, default_bm);
+                        self.infer_pat(*pat, &expected, default_bm);
                     }
                     ty
                 } else {
@@ -173,13 +174,13 @@ impl<'a> InferenceContext<'a> {
             Pat::TupleStruct { path: p, args: subpats, ellipsis } => self.infer_tuple_struct_pat(
                 p.as_deref(),
                 subpats,
-                expected,
+                &expected,
                 default_bm,
                 pat,
                 *ellipsis,
             ),
             Pat::Record { path: p, args: fields, ellipsis: _ } => {
-                self.infer_record_pat(p.as_deref(), fields, expected, default_bm, pat)
+                self.infer_record_pat(p.as_deref(), fields, &expected, default_bm, pat)
             }
             Pat::Path(path) => {
                 // FIXME use correct resolver for the surrounding expression
@@ -193,7 +194,7 @@ impl<'a> InferenceContext<'a> {
                     BindingMode::convert(*mode)
                 };
                 let inner_ty = if let Some(subpat) = subpat {
-                    self.infer_pat(*subpat, expected, default_bm)
+                    self.infer_pat(*subpat, &expected, default_bm)
                 } else {
                     expected.clone()
                 };
@@ -206,7 +207,6 @@ impl<'a> InferenceContext<'a> {
                     }
                     BindingMode::Move => inner_ty.clone(),
                 };
-                let bound_ty = self.resolve_ty_as_possible(bound_ty);
                 self.write_pat_ty(pat, bound_ty);
                 return inner_ty;
             }
@@ -265,13 +265,12 @@ impl<'a> InferenceContext<'a> {
         };
         // use a new type variable if we got error type here
         let ty = self.insert_type_vars_shallow(ty);
-        if !self.unify(&ty, expected) {
+        if !self.unify(&ty, &expected) {
             self.result.type_mismatches.insert(
                 pat.into(),
                 TypeMismatch { expected: expected.clone(), actual: ty.clone() },
             );
         }
-        let ty = self.resolve_ty_as_possible(ty);
         self.write_pat_ty(pat, ty.clone());
         ty
     }
diff --git a/crates/hir_ty/src/infer/path.rs b/crates/hir_ty/src/infer/path.rs
index fd366e121..14c99eafd 100644
--- a/crates/hir_ty/src/infer/path.rs
+++ b/crates/hir_ty/src/infer/path.rs
@@ -65,7 +65,6 @@ impl<'a> InferenceContext<'a> {
         let typable: ValueTyDefId = match value {
             ValueNs::LocalBinding(pat) => {
                 let ty = self.result.type_of_pat.get(pat)?.clone();
-                let ty = self.resolve_ty_as_possible(ty);
                 return Some(ty);
             }
             ValueNs::FunctionId(it) => it.into(),
@@ -275,6 +274,7 @@ impl<'a> InferenceContext<'a> {
         name: &Name,
         id: ExprOrPatId,
     ) -> Option<(ValueNs, Option<Substitution>)> {
+        let ty = self.resolve_ty_shallow(ty);
         let (enum_id, subst) = match ty.as_adt() {
             Some((AdtId::EnumId(e), subst)) => (e, subst),
             _ => return None,
diff --git a/crates/hir_ty/src/infer/unify.rs b/crates/hir_ty/src/infer/unify.rs
index 278127c69..539e12420 100644
--- a/crates/hir_ty/src/infer/unify.rs
+++ b/crates/hir_ty/src/infer/unify.rs
@@ -24,6 +24,9 @@ impl<'a> InferenceContext<'a> {
     where
         T::Result: HasInterner<Interner = Interner>,
     {
+        // try to resolve obligations before canonicalizing, since this might
+        // result in new knowledge about variables
+        self.resolve_obligations_as_possible();
         self.table.canonicalize(t)
     }
 }
@@ -216,7 +219,6 @@ impl<'a> InferenceTable<'a> {
     /// call). `make_ty` handles this already, but e.g. for field types we need
     /// to do it as well.
     pub(super) fn normalize_associated_types_in(&mut self, ty: Ty) -> Ty {
-        let ty = self.resolve_ty_as_possible(ty);
         fold_tys(
             ty,
             |ty, _| match ty.kind(&Interner) {
@@ -302,11 +304,6 @@ impl<'a> InferenceTable<'a> {
         self.resolve_with_fallback(ty, |_, _, d, _| d)
     }
 
-    // FIXME get rid of this, instead resolve shallowly where necessary
-    pub(crate) fn resolve_ty_as_possible(&mut self, ty: Ty) -> Ty {
-        self.resolve_ty_as_possible_inner(&mut Vec::new(), ty)
-    }
-
     /// Unify two types and register new trait goals that arise from that.
     // TODO give these two functions better names
     pub(crate) fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
@@ -344,36 +341,6 @@ impl<'a> InferenceTable<'a> {
         self.var_unification_table.normalize_ty_shallow(&Interner, ty).unwrap_or_else(|| ty.clone())
     }
 
-    /// Resolves the type as far as currently possible, replacing type variables
-    /// by their known types.
-    fn resolve_ty_as_possible_inner(&mut self, tv_stack: &mut Vec<InferenceVar>, ty: Ty) -> Ty {
-        fold_tys(
-            ty,
-            |ty, _| match ty.kind(&Interner) {
-                &TyKind::InferenceVar(tv, kind) => {
-                    if tv_stack.contains(&tv) {
-                        // recursive type
-                        return self.type_variable_table.fallback_value(tv, kind);
-                    }
-                    if let Some(known_ty) = self.var_unification_table.probe_var(tv) {
-                        // known_ty may contain other variables that are known by now
-                        tv_stack.push(tv);
-                        let result = self.resolve_ty_as_possible_inner(
-                            tv_stack,
-                            known_ty.assert_ty_ref(&Interner).clone(),
-                        );
-                        tv_stack.pop();
-                        result
-                    } else {
-                        ty
-                    }
-                }
-                _ => ty,
-            },
-            DebruijnIndex::INNERMOST,
-        )
-    }
-
     pub fn register_obligation(&mut self, goal: Goal) {
         let in_env = InEnvironment::new(&self.trait_env.env, goal);
         self.register_obligation_in_env(in_env)
diff --git a/crates/hir_ty/src/tests/regression.rs b/crates/hir_ty/src/tests/regression.rs
index 59a16f390..baef81590 100644
--- a/crates/hir_ty/src/tests/regression.rs
+++ b/crates/hir_ty/src/tests/regression.rs
@@ -117,19 +117,19 @@ fn recursive_vars_2() {
         "#,
         expect![[r#"
             10..79 '{     ...x)]; }': ()
-            20..21 'x': {unknown}
-            24..31 'unknown': {unknown}
+            20..21 'x': &{unknown}
+            24..31 'unknown': &{unknown}
             41..42 'y': {unknown}
             45..52 'unknown': {unknown}
-            58..76 '[(x, y..., &x)]': [({unknown}, {unknown}); 2]
-            59..65 '(x, y)': ({unknown}, {unknown})
-            60..61 'x': {unknown}
+            58..76 '[(x, y..., &x)]': [(&{unknown}, {unknown}); 2]
+            59..65 '(x, y)': (&{unknown}, {unknown})
+            60..61 'x': &{unknown}
             63..64 'y': {unknown}
-            67..75 '(&y, &x)': (&{unknown}, &{unknown})
+            67..75 '(&y, &x)': (&{unknown}, {unknown})
             68..70 '&y': &{unknown}
             69..70 'y': {unknown}
-            72..74 '&x': &{unknown}
-            73..74 'x': {unknown}
+            72..74 '&x': &&{unknown}
+            73..74 'x': &{unknown}
         "#]],
     );
 }
diff --git a/crates/hir_ty/src/tests/traits.rs b/crates/hir_ty/src/tests/traits.rs
index f80cf9879..a5a2df54c 100644
--- a/crates/hir_ty/src/tests/traits.rs
+++ b/crates/hir_ty/src/tests/traits.rs
@@ -3104,7 +3104,7 @@ fn foo() {
             568..573 'f(&s)': FnOnce::Output<dyn FnOnce(&Option<i32>), (&Option<i32>,)>
             570..572 '&s': &Option<i32>
             571..572 's': Option<i32>
-            549..562: expected Box<dyn FnOnce(&Option<i32>)>, got Box<|_| -> ()>
+            549..562: expected Box<dyn FnOnce(&Option<i32>)>, got Box<|{unknown}| -> ()>
         "#]],
     );
 }