7 files changed, 39 insertions, 25 deletions

diff --git a/crates/hir_ty/src/chalk_ext.rs b/crates/hir_ty/src/chalk_ext.rs
new file mode 100644
index 000000000..b7463366b
--- /dev/null
+++ b/crates/hir_ty/src/chalk_ext.rs
@@ -0,0 +1,13 @@
+//! Various extensions traits for Chalk types.
+
+use crate::{Interner, Ty, TyKind};
+
+pub trait TyExt {
+    fn is_unit(&self) -> bool;
+}
+
+impl TyExt for Ty {
+    fn is_unit(&self) -> bool {
+        matches!(self.kind(&Interner), TyKind::Tuple(0, _))
+    }
+}
diff --git a/crates/hir_ty/src/diagnostics/expr.rs b/crates/hir_ty/src/diagnostics/expr.rs
index ad1259b34..8169b759f 100644
--- a/crates/hir_ty/src/diagnostics/expr.rs
+++ b/crates/hir_ty/src/diagnostics/expr.rs
@@ -15,7 +15,7 @@ use crate::{
         MissingPatFields, RemoveThisSemicolon,
     },
     utils::variant_data,
-    AdtId, InferenceResult, Interner, Ty, TyKind,
+    AdtId, InferenceResult, Interner, TyExt, TyKind,
 };
 
 pub(crate) use hir_def::{
@@ -423,7 +423,7 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
             None => return,
         };
 
-        if mismatch.actual != Ty::unit() || mismatch.expected != *possible_tail_ty {
+        if !mismatch.actual.is_unit() || mismatch.expected != *possible_tail_ty {
             return;
         }
 
diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index 97f1092c6..eb82e1a11 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -19,7 +19,8 @@ use crate::{
     db::HirDatabase, from_assoc_type_id, from_foreign_def_id, from_placeholder_idx, primitive,
     to_assoc_type_id, traits::chalk::from_chalk, utils::generics, AdtId, AliasEq, AliasTy,
     CallableDefId, CallableSig, DomainGoal, GenericArg, ImplTraitId, Interner, Lifetime, OpaqueTy,
-    ProjectionTy, QuantifiedWhereClause, Scalar, Substitution, TraitRef, Ty, TyKind, WhereClause,
+    ProjectionTy, QuantifiedWhereClause, Scalar, Substitution, TraitRef, Ty, TyExt, TyKind,
+    WhereClause,
 };
 
 pub struct HirFormatter<'a> {
@@ -423,7 +424,7 @@ impl HirDisplay for Ty {
                 f.write_joined(sig.params(), ", ")?;
                 write!(f, ")")?;
                 let ret = sig.ret();
-                if *ret != Ty::unit() {
+                if !ret.is_unit() {
                     let ret_display = ret.into_displayable(
                         f.db,
                         f.max_size,
@@ -663,7 +664,7 @@ impl HirDisplay for CallableSig {
         }
         write!(f, ")")?;
         let ret = self.ret();
-        if *ret != Ty::unit() {
+        if !ret.is_unit() {
             let ret_display =
                 ret.into_displayable(f.db, f.max_size, f.omit_verbose_types, f.display_target);
             write!(f, " -> {}", ret_display)?;
diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index dd3914ec3..db8aeead2 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -23,7 +23,7 @@ use crate::{
     traits::{chalk::from_chalk, FnTrait, InEnvironment},
     utils::{generics, variant_data, Generics},
     AdtId, Binders, CallableDefId, DomainGoal, FnPointer, FnSig, Interner, Rawness, Scalar,
-    Substitution, TraitRef, Ty, TyKind,
+    Substitution, TraitRef, Ty, TyBuilder, TyKind,
 };
 
 use super::{
@@ -138,7 +138,7 @@ impl<'a> InferenceContext<'a> {
                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
                 let else_ty = match else_branch {
                     Some(else_branch) => self.infer_expr_inner(*else_branch, &expected),
-                    None => Ty::unit(),
+                    None => TyBuilder::unit(),
                 };
                 both_arms_diverge &= self.diverges;
 
@@ -193,7 +193,7 @@ impl<'a> InferenceContext<'a> {
                     break_ty: self.table.new_type_var(),
                     label: label.map(|label| self.body[label].name.clone()),
                 });
-                self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
+                self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 
                 let ctxt = self.breakables.pop().expect("breakable stack broken");
                 if ctxt.may_break {
@@ -217,11 +217,11 @@ impl<'a> InferenceContext<'a> {
                     *condition,
                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
                 );
-                self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
+                self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
                 // the body may not run, so it diverging doesn't mean we diverge
                 self.diverges = Diverges::Maybe;
-                Ty::unit()
+                TyBuilder::unit()
             }
             Expr::For { iterable, body, pat, label } => {
                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
@@ -236,11 +236,11 @@ impl<'a> InferenceContext<'a> {
 
                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 
-                self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
+                self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
                 // the body may not run, so it diverging doesn't mean we diverge
                 self.diverges = Diverges::Maybe;
-                Ty::unit()
+                TyBuilder::unit()
             }
             Expr::Lambda { body, args, ret_type, arg_types } => {
                 assert_eq!(args.len(), arg_types.len());
@@ -360,7 +360,7 @@ impl<'a> InferenceContext<'a> {
                 let val_ty = if let Some(expr) = expr {
                     self.infer_expr(*expr, &Expectation::none())
                 } else {
-                    Ty::unit()
+                    TyBuilder::unit()
                 };
 
                 let last_ty =
@@ -386,7 +386,7 @@ impl<'a> InferenceContext<'a> {
                 if let Some(expr) = expr {
                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
                 } else {
-                    let unit = Ty::unit();
+                    let unit = TyBuilder::unit();
                     self.coerce(&unit, &self.return_ty.clone());
                 }
                 TyKind::Never.intern(&Interner)
@@ -828,8 +828,8 @@ impl<'a> InferenceContext<'a> {
                 // we don't even make an attempt at coercion
                 self.table.new_maybe_never_var()
             } else {
-                self.coerce(&Ty::unit(), &expected.coercion_target());
-                Ty::unit()
+                self.coerce(&TyBuilder::unit(), &expected.coercion_target());
+                TyBuilder::unit()
             }
         };
         ty
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index a8ddb43f5..b6173d87c 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -23,6 +23,7 @@ pub mod diagnostics;
 mod tests;
 #[cfg(test)]
 mod test_db;
+mod chalk_ext;
 
 use std::{iter, mem, sync::Arc};
 
@@ -42,6 +43,7 @@ use crate::{
 };
 
 pub use autoderef::autoderef;
+pub use chalk_ext::TyExt;
 pub use infer::{could_unify, InferenceResult, InferenceVar};
 pub use lower::{
     associated_type_shorthand_candidates, callable_item_sig, CallableDefId, ImplTraitLoweringMode,
@@ -813,14 +815,12 @@ impl TypeWalk for CallableSig {
 struct TyBuilder {}
 
 impl TyBuilder {
-
-}
-
-impl Ty {
-    pub fn unit() -> Self {
+    pub fn unit() -> Ty {
         TyKind::Tuple(0, Substitution::empty(&Interner)).intern(&Interner)
     }
+}
 
+impl Ty {
     pub fn adt_ty(adt: hir_def::AdtId, substs: Substitution) -> Ty {
         TyKind::Adt(AdtId(adt), substs).intern(&Interner)
     }
diff --git a/crates/hir_ty/src/op.rs b/crates/hir_ty/src/op.rs
index 8533e1ed8..90dd31a35 100644
--- a/crates/hir_ty/src/op.rs
+++ b/crates/hir_ty/src/op.rs
@@ -2,12 +2,12 @@
 use chalk_ir::TyVariableKind;
 use hir_def::expr::{ArithOp, BinaryOp, CmpOp};
 
-use crate::{Interner, Scalar, Ty, TyKind};
+use crate::{Interner, Scalar, Ty, TyBuilder, TyKind};
 
 pub(super) fn binary_op_return_ty(op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Ty {
     match op {
         BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
-        BinaryOp::Assignment { .. } => Ty::unit(),
+        BinaryOp::Assignment { .. } => TyBuilder::unit(),
         BinaryOp::ArithOp(ArithOp::Shl) | BinaryOp::ArithOp(ArithOp::Shr) => {
             match lhs_ty.kind(&Interner) {
                 TyKind::Scalar(Scalar::Int(_))
diff --git a/crates/hir_ty/src/traits/chalk.rs b/crates/hir_ty/src/traits/chalk.rs
index fbac51b05..36a397990 100644
--- a/crates/hir_ty/src/traits/chalk.rs
+++ b/crates/hir_ty/src/traits/chalk.rs
@@ -22,7 +22,7 @@ use crate::{
     to_assoc_type_id, to_chalk_trait_id,
     utils::generics,
     AliasEq, AliasTy, BoundVar, CallableDefId, DebruijnIndex, FnDefId, ProjectionTy, Substitution,
-    TraitRef, Ty, TyKind, WhereClause,
+    TraitRef, Ty, TyBuilder, TyKind, WhereClause,
 };
 use mapping::{
     convert_where_clauses, generic_predicate_to_inline_bound, make_binders, TypeAliasAsValue,
@@ -300,7 +300,7 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
         _closure_id: chalk_ir::ClosureId<Interner>,
         _substs: &chalk_ir::Substitution<Interner>,
     ) -> chalk_ir::Binders<chalk_ir::Ty<Interner>> {
-        let ty = Ty::unit().to_chalk(self.db);
+        let ty = TyBuilder::unit().to_chalk(self.db);
         make_binders(ty, 0)
     }
     fn closure_fn_substitution(