]> git.lizzy.rs Git - rust.git/blobdiff - crates/hir_ty/src/infer/expr.rs
Merge #11481
[rust.git] / crates / hir_ty / src / infer / expr.rs
index b2570b97f902eaa334fe4b38e4fc5141f1d4d07a..13f64d682521e8733ec67b6fd2edb44990f02736 100644 (file)
@@ -8,10 +8,10 @@
 
 use chalk_ir::{cast::Cast, fold::Shift, Mutability, TyVariableKind};
 use hir_def::{
-    expr::{Array, BinaryOp, Expr, ExprId, Literal, MatchGuard, Statement, UnaryOp},
+    expr::{ArithOp, Array, BinaryOp, CmpOp, Expr, ExprId, Literal, Ordering, Statement, UnaryOp},
     path::{GenericArg, GenericArgs},
     resolver::resolver_for_expr,
-    AssocContainerId, FieldId, Lookup,
+    FieldId, FunctionId, ItemContainerId, Lookup,
 };
 use hir_expand::name::{name, Name};
 use stdx::always;
@@ -23,7 +23,7 @@
     infer::coerce::CoerceMany,
     lower::lower_to_chalk_mutability,
     mapping::from_chalk,
-    method_resolution, op,
+    method_resolution,
     primitive::{self, UintTy},
     static_lifetime, to_chalk_trait_id,
     traits::FnTrait,
@@ -60,7 +60,7 @@ pub(super) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) ->
     /// Return the type after possible coercion.
     pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
         let ty = self.infer_expr_inner(expr, expected);
-        let ty = if let Some(target) = expected.only_has_type(&mut self.table) {
+        if let Some(target) = expected.only_has_type(&mut self.table) {
             match self.coerce(Some(expr), &ty, &target) {
                 Ok(res) => res.value,
                 Err(_) => {
@@ -74,9 +74,7 @@ pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation)
             }
         } else {
             ty
-        };
-
-        ty
+        }
     }
 
     fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
@@ -104,11 +102,11 @@ fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Ve
 
         let trait_env = self.trait_env.env.clone();
         let obligation = InEnvironment {
-            goal: projection.trait_ref(self.db).cast(&Interner),
+            goal: projection.trait_ref(self.db).cast(Interner),
             environment: trait_env,
         };
         let canonical = self.canonicalize(obligation.clone());
-        if self.db.trait_solve(krate, canonical.value.cast(&Interner)).is_some() {
+        if self.db.trait_solve(krate, canonical.value.cast(Interner)).is_some() {
             self.push_obligation(obligation.goal);
             let return_ty = self.table.normalize_projection_ty(projection);
             Some((arg_tys, return_ty))
@@ -134,7 +132,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                 // if let is desugared to match, so this is always simple if
                 self.infer_expr(
                     condition,
-                    &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
+                    &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
                 );
 
                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
@@ -157,6 +155,11 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
 
                 coerce.complete()
             }
+            &Expr::Let { pat, expr } => {
+                let input_ty = self.infer_expr(expr, &Expectation::none());
+                self.infer_pat(pat, &input_ty, BindingMode::default());
+                TyKind::Scalar(Scalar::Bool).intern(Interner)
+            }
             Expr::Block { statements, tail, label, id: _ } => {
                 let old_resolver = mem::replace(
                     &mut self.resolver,
@@ -200,8 +203,8 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                 let inner_ty = self.infer_expr(*body, &Expectation::none());
                 let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
                 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
-                TyKind::OpaqueType(opaque_ty_id, Substitution::from1(&Interner, inner_ty))
-                    .intern(&Interner)
+                TyKind::OpaqueType(opaque_ty_id, Substitution::from1(Interner, inner_ty))
+                    .intern(Interner)
             }
             Expr::Loop { body, label } => {
                 self.breakables.push(BreakableContext {
@@ -217,7 +220,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                     self.diverges = Diverges::Maybe;
                     ctxt.coerce.complete()
                 } else {
-                    TyKind::Never.intern(&Interner)
+                    TyKind::Never.intern(Interner)
                 }
             }
             Expr::While { condition, body, label } => {
@@ -229,7 +232,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                 // while let is desugared to a match loop, so this is always simple while
                 self.infer_expr(
                     *condition,
-                    &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
+                    &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
                 );
                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
@@ -263,10 +266,9 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
 
                 // collect explicitly written argument types
                 for arg_type in arg_types.iter() {
-                    let arg_ty = if let Some(type_ref) = arg_type {
-                        self.make_ty(type_ref)
-                    } else {
-                        self.table.new_type_var()
+                    let arg_ty = match arg_type {
+                        Some(type_ref) => self.make_ty(type_ref),
+                        None => self.table.new_type_var(),
                     };
                     sig_tys.push(arg_ty);
                 }
@@ -281,14 +283,14 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                     num_binders: 0,
                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
                     substitution: FnSubst(
-                        Substitution::from_iter(&Interner, sig_tys.clone()).shifted_in(&Interner),
+                        Substitution::from_iter(Interner, sig_tys.clone()).shifted_in(Interner),
                     ),
                 })
-                .intern(&Interner);
+                .intern(Interner);
                 let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
                 let closure_ty =
-                    TyKind::Closure(closure_id, Substitution::from1(&Interner, sig_ty.clone()))
-                        .intern(&Interner);
+                    TyKind::Closure(closure_id, Substitution::from1(Interner, sig_ty.clone()))
+                        .intern(Interner);
 
                 // Eagerly try to relate the closure type with the expected
                 // type, otherwise we often won't have enough information to
@@ -327,10 +329,8 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                     },
                 );
                 let res = derefs.by_ref().find_map(|(callee_deref_ty, _)| {
-                    self.callable_sig(
-                        &canonicalized.decanonicalize_ty(callee_deref_ty.value),
-                        args.len(),
-                    )
+                    let ty = &canonicalized.decanonicalize_ty(&mut self.table, callee_deref_ty);
+                    self.callable_sig(ty, args.len())
                 });
                 let (param_tys, ret_ty): (Vec<Ty>, Ty) = match res {
                     Some(res) => {
@@ -340,18 +340,32 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                     None => (Vec::new(), self.err_ty()),
                 };
                 self.register_obligations_for_call(&callee_ty);
-                self.check_call_arguments(args, &param_tys);
+
+                let expected_inputs = self.expected_inputs_for_expected_output(
+                    expected,
+                    ret_ty.clone(),
+                    param_tys.clone(),
+                );
+
+                self.check_call_arguments(args, &expected_inputs, &param_tys);
                 self.normalize_associated_types_in(ret_ty)
             }
             Expr::MethodCall { receiver, args, method_name, generic_args } => self
-                .infer_method_call(tgt_expr, *receiver, args, method_name, generic_args.as_deref()),
+                .infer_method_call(
+                    tgt_expr,
+                    *receiver,
+                    args,
+                    method_name,
+                    generic_args.as_deref(),
+                    expected,
+                ),
             Expr::Match { expr, arms } => {
                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 
                 let expected = expected.adjust_for_branches(&mut self.table);
 
                 let result_ty = if arms.is_empty() {
-                    TyKind::Never.intern(&Interner)
+                    TyKind::Never.intern(Interner)
                 } else {
                     match &expected {
                         Expectation::HasType(ty) => ty.clone(),
@@ -363,23 +377,14 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                 let matchee_diverges = self.diverges;
                 let mut all_arms_diverge = Diverges::Always;
 
-                for arm in arms {
+                for arm in arms.iter() {
                     self.diverges = Diverges::Maybe;
                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
-                    match arm.guard {
-                        Some(MatchGuard::If { expr: guard_expr }) => {
-                            self.infer_expr(
-                                guard_expr,
-                                &Expectation::has_type(
-                                    TyKind::Scalar(Scalar::Bool).intern(&Interner),
-                                ),
-                            );
-                        }
-                        Some(MatchGuard::IfLet { expr, pat }) => {
-                            let input_ty = self.infer_expr(expr, &Expectation::none());
-                            let _pat_ty = self.infer_pat(pat, &input_ty, BindingMode::default());
-                        }
-                        _ => {}
+                    if let Some(guard_expr) = arm.guard {
+                        self.infer_expr(
+                            guard_expr,
+                            &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
+                        );
                     }
 
                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
@@ -396,7 +401,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or_else(|| self.err_ty())
             }
-            Expr::Continue { .. } => TyKind::Never.intern(&Interner),
+            Expr::Continue { .. } => TyKind::Never.intern(Interner),
             Expr::Break { expr, label } => {
                 let mut coerce = match find_breakable(&mut self.breakables, label.as_ref()) {
                     Some(ctxt) => {
@@ -427,7 +432,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                     });
                 };
 
-                TyKind::Never.intern(&Interner)
+                TyKind::Never.intern(Interner)
             }
             Expr::Return { expr } => {
                 if let Some(expr) = expr {
@@ -436,14 +441,14 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                     let unit = TyBuilder::unit();
                     let _ = self.coerce(Some(tgt_expr), &unit, &self.return_ty.clone());
                 }
-                TyKind::Never.intern(&Interner)
+                TyKind::Never.intern(Interner)
             }
             Expr::Yield { expr } => {
                 // FIXME: track yield type for coercion
                 if let Some(expr) = expr {
                     self.infer_expr(*expr, &Expectation::none());
                 }
-                TyKind::Never.intern(&Interner)
+                TyKind::Never.intern(Interner)
             }
             Expr::RecordLit { path, fields, spread } => {
                 let (ty, def_id) = self.resolve_variant(path.as_deref(), false);
@@ -458,7 +463,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                 let substs = ty
                     .as_adt()
                     .map(|(_, s)| s.clone())
-                    .unwrap_or_else(|| Substitution::empty(&Interner));
+                    .unwrap_or_else(|| Substitution::empty(Interner));
                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
                 let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
                 for field in fields.iter() {
@@ -473,7 +478,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                             }
                         });
                     let field_ty = field_def.map_or(self.err_ty(), |it| {
-                        field_types[it.local_id].clone().substitute(&Interner, &substs)
+                        field_types[it.local_id].clone().substitute(Interner, &substs)
                     });
                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
                 }
@@ -495,22 +500,25 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                     },
                 );
                 let ty = autoderef.by_ref().find_map(|(derefed_ty, _)| {
-                    let def_db = self.db.upcast();
                     let module = self.resolver.module();
+                    let db = self.db;
                     let is_visible = |field_id: &FieldId| {
                         module
                             .map(|mod_id| {
-                                self.db.field_visibilities(field_id.parent)[field_id.local_id]
-                                    .is_visible_from(def_db, mod_id)
+                                db.field_visibilities(field_id.parent)[field_id.local_id]
+                                    .is_visible_from(db.upcast(), mod_id)
                             })
                             .unwrap_or(true)
                     };
-                    match canonicalized.decanonicalize_ty(derefed_ty.value).kind(&Interner) {
+                    match canonicalized
+                        .decanonicalize_ty(&mut self.table, derefed_ty)
+                        .kind(Interner)
+                    {
                         TyKind::Tuple(_, substs) => name.as_tuple_index().and_then(|idx| {
                             substs
-                                .as_slice(&Interner)
+                                .as_slice(Interner)
                                 .get(idx)
-                                .map(|a| a.assert_ty_ref(&Interner))
+                                .map(|a| a.assert_ty_ref(Interner))
                                 .cloned()
                         }),
                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
@@ -521,7 +529,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                                 Some(
                                     self.db.field_types((*s).into())[field.local_id]
                                         .clone()
-                                        .substitute(&Interner, &parameters),
+                                        .substitute(Interner, &parameters),
                                 )
                             } else {
                                 None
@@ -535,7 +543,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                                 Some(
                                     self.db.field_types((*u).into())[field.local_id]
                                         .clone()
-                                        .substitute(&Interner, &parameters),
+                                        .substitute(Interner, &parameters),
                                 )
                             } else {
                                 None
@@ -584,7 +592,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                         // FIXME: record type error - expected reference but found ptr,
                         // which cannot be coerced
                     }
-                    Expectation::rvalue_hint(Ty::clone(exp_inner))
+                    Expectation::rvalue_hint(&mut self.table, Ty::clone(exp_inner))
                 } else {
                     Expectation::none()
                 };
@@ -593,7 +601,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
                     Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
                 }
-                .intern(&Interner)
+                .intern(Interner)
             }
             Expr::Box { expr } => {
                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
@@ -622,7 +630,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                                 },
                             ) {
                                 Some(derefed_ty) => {
-                                    canonicalized.decanonicalize_ty(derefed_ty.value)
+                                    canonicalized.decanonicalize_ty(&mut self.table, derefed_ty)
                                 }
                                 None => self.err_ty(),
                             }
@@ -630,7 +638,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                         None => self.err_ty(),
                     },
                     UnaryOp::Neg => {
-                        match inner_ty.kind(&Interner) {
+                        match inner_ty.kind(Interner) {
                             // Fast path for builtins
                             TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_))
                             | TyKind::InferenceVar(
@@ -643,7 +651,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                         }
                     }
                     UnaryOp::Not => {
-                        match inner_ty.kind(&Interner) {
+                        match inner_ty.kind(Interner) {
                             // Fast path for builtins
                             TyKind::Scalar(Scalar::Bool | Scalar::Int(_) | Scalar::Uint(_))
                             | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
@@ -655,33 +663,21 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                 }
             }
             Expr::BinaryOp { lhs, rhs, op } => match op {
-                Some(op) => {
-                    let lhs_expectation = match op {
-                        BinaryOp::LogicOp(..) => {
-                            Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner))
-                        }
-                        _ => 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());
-
-                    if ret.is_unknown() {
-                        cov_mark::hit!(infer_expr_inner_binary_operator_overload);
-
-                        self.resolve_associated_type_with_params(
-                            lhs_ty,
-                            self.resolve_binary_op_output(op),
-                            &[rhs_ty],
-                        )
-                    } else {
-                        ret
-                    }
+                Some(BinaryOp::Assignment { op: None }) => {
+                    let lhs_ty = self.infer_expr(*lhs, &Expectation::none());
+                    self.infer_expr_coerce(*rhs, &Expectation::has_type(lhs_ty));
+                    self.result.standard_types.unit.clone()
+                }
+                Some(BinaryOp::LogicOp(_)) => {
+                    let bool_ty = self.result.standard_types.bool_.clone();
+                    self.infer_expr_coerce(*lhs, &Expectation::HasType(bool_ty.clone()));
+                    let lhs_diverges = self.diverges;
+                    self.infer_expr_coerce(*rhs, &Expectation::HasType(bool_ty.clone()));
+                    // Depending on the LHS' value, the RHS can never execute.
+                    self.diverges = lhs_diverges;
+                    bool_ty
                 }
+                Some(op) => self.infer_overloadable_binop(*lhs, *op, *rhs, tgt_expr),
                 _ => self.err_ty(),
             },
             Expr::Range { lhs, rhs, range_type } => {
@@ -737,8 +733,9 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                         krate,
                         index_trait,
                     );
-                    let self_ty =
-                        self_ty.map_or(self.err_ty(), |t| canonicalized.decanonicalize_ty(t.value));
+                    let self_ty = self_ty.map_or(self.err_ty(), |t| {
+                        canonicalized.decanonicalize_ty(&mut self.table, t)
+                    });
                     self.resolve_associated_type_with_params(
                         self_ty,
                         self.resolve_ops_index_output(),
@@ -752,11 +749,11 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                 let mut tys = match expected
                     .only_has_type(&mut self.table)
                     .as_ref()
-                    .map(|t| t.kind(&Interner))
+                    .map(|t| t.kind(Interner))
                 {
                     Some(TyKind::Tuple(_, substs)) => substs
-                        .iter(&Interner)
-                        .map(|a| a.assert_ty_ref(&Interner).clone())
+                        .iter(Interner)
+                        .map(|a| a.assert_ty_ref(Interner).clone())
                         .chain(repeat_with(|| self.table.new_type_var()))
                         .take(exprs.len())
                         .collect::<Vec<_>>(),
@@ -767,11 +764,11 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
                 }
 
-                TyKind::Tuple(tys.len(), Substitution::from_iter(&Interner, tys)).intern(&Interner)
+                TyKind::Tuple(tys.len(), Substitution::from_iter(Interner, tys)).intern(Interner)
             }
             Expr::Array(array) => {
                 let elem_ty =
-                    match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(&Interner)) {
+                    match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(Interner)) {
                         Some(TyKind::Array(st, _) | TyKind::Slice(st)) => st.clone(),
                         _ => self.table.new_type_var(),
                     };
@@ -791,50 +788,57 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                         self.infer_expr(
                             repeat,
                             &Expectation::has_type(
-                                TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner),
+                                TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(Interner),
                             ),
                         );
 
-                        let repeat_expr = &self.body.exprs[repeat];
-                        consteval::eval_usize(repeat_expr)
+                        consteval::eval_usize(
+                            repeat,
+                            consteval::ConstEvalCtx {
+                                exprs: &body.exprs,
+                                pats: &body.pats,
+                                local_data: Default::default(),
+                                infer: &mut |x| self.infer_expr(x, &expected),
+                            },
+                        )
                     }
                 };
 
-                TyKind::Array(coerce.complete(), consteval::usize_const(len)).intern(&Interner)
+                TyKind::Array(coerce.complete(), consteval::usize_const(len)).intern(Interner)
             }
             Expr::Literal(lit) => match lit {
-                Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
+                Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
                 Literal::String(..) => {
-                    TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(&Interner))
-                        .intern(&Interner)
+                    TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(Interner))
+                        .intern(Interner)
                 }
                 Literal::ByteString(bs) => {
-                    let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(&Interner);
+                    let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner);
 
                     let len = consteval::usize_const(Some(bs.len() as u64));
 
-                    let array_type = TyKind::Array(byte_type, len).intern(&Interner);
-                    TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(&Interner)
+                    let array_type = TyKind::Array(byte_type, len).intern(Interner);
+                    TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(Interner)
                 }
-                Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(&Interner),
+                Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(Interner),
                 Literal::Int(_v, ty) => match ty {
                     Some(int_ty) => {
                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
-                            .intern(&Interner)
+                            .intern(Interner)
                     }
                     None => self.table.new_integer_var(),
                 },
                 Literal::Uint(_v, ty) => match ty {
                     Some(int_ty) => {
                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
-                            .intern(&Interner)
+                            .intern(Interner)
                     }
                     None => self.table.new_integer_var(),
                 },
                 Literal::Float(_v, ty) => match ty {
                     Some(float_ty) => {
                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
-                            .intern(&Interner)
+                            .intern(Interner)
                     }
                     None => self.table.new_float_var(),
                 },
@@ -847,6 +851,60 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
         ty
     }
 
+    fn infer_overloadable_binop(
+        &mut self,
+        lhs: ExprId,
+        op: BinaryOp,
+        rhs: ExprId,
+        tgt_expr: ExprId,
+    ) -> Ty {
+        let lhs_expectation = Expectation::none();
+        let lhs_ty = self.infer_expr(lhs, &lhs_expectation);
+        let rhs_ty = self.table.new_type_var();
+
+        let func = self.resolve_binop_method(op);
+        let func = match func {
+            Some(func) => func,
+            None => {
+                let rhs_ty = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone());
+                let rhs_ty = self.infer_expr_coerce(rhs, &Expectation::from_option(rhs_ty));
+                return self
+                    .builtin_binary_op_return_ty(op, lhs_ty, rhs_ty)
+                    .unwrap_or_else(|| self.err_ty());
+            }
+        };
+
+        let subst = TyBuilder::subst_for_def(self.db, func)
+            .push(lhs_ty.clone())
+            .push(rhs_ty.clone())
+            .build();
+        self.write_method_resolution(tgt_expr, func, subst.clone());
+
+        let method_ty = self.db.value_ty(func.into()).substitute(Interner, &subst);
+        self.register_obligations_for_call(&method_ty);
+
+        self.infer_expr_coerce(rhs, &Expectation::has_type(rhs_ty.clone()));
+
+        let ret_ty = match method_ty.callable_sig(self.db) {
+            Some(sig) => sig.ret().clone(),
+            None => self.err_ty(),
+        };
+
+        let ret_ty = self.normalize_associated_types_in(ret_ty);
+
+        // FIXME: record autoref adjustments
+
+        // use knowledge of built-in binary ops, which can sometimes help inference
+        if let Some(builtin_rhs) = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone()) {
+            self.unify(&builtin_rhs, &rhs_ty);
+        }
+        if let Some(builtin_ret) = self.builtin_binary_op_return_ty(op, lhs_ty, rhs_ty) {
+            self.unify(&builtin_ret, &ret_ty);
+        }
+
+        ret_ty
+    }
+
     fn infer_block(
         &mut self,
         expr: ExprId,
@@ -856,7 +914,7 @@ fn infer_block(
     ) -> Ty {
         for stmt in statements {
             match stmt {
-                Statement::Let { pat, type_ref, initializer } => {
+                Statement::Let { pat, type_ref, initializer, else_branch } => {
                     let decl_ty = type_ref
                         .as_ref()
                         .map(|tr| self.make_ty(tr))
@@ -873,6 +931,13 @@ fn infer_block(
                         }
                     }
 
+                    if let Some(expr) = else_branch {
+                        self.infer_expr_coerce(
+                            *expr,
+                            &Expectation::has_type(Ty::new(Interner, TyKind::Never)),
+                        );
+                    }
+
                     self.infer_pat(*pat, &ty, BindingMode::default());
                 }
                 Statement::Expr { expr, .. } => {
@@ -881,7 +946,7 @@ fn infer_block(
             }
         }
 
-        let ty = if let Some(expr) = tail {
+        if let Some(expr) = tail {
             self.infer_expr_coerce(expr, expected)
         } else {
             // Citing rustc: if there is no explicit tail expression,
@@ -900,8 +965,7 @@ fn infer_block(
                 }
                 TyBuilder::unit()
             }
-        };
-        ty
+        }
     }
 
     fn infer_method_call(
@@ -911,6 +975,7 @@ fn infer_method_call(
         args: &[ExprId],
         method_name: &Name,
         generic_args: Option<&GenericArgs>,
+        expected: &Expectation,
     ) -> Ty {
         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
         let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
@@ -924,13 +989,13 @@ fn infer_method_call(
                 self.trait_env.clone(),
                 krate,
                 &traits_in_scope,
-                self.resolver.module(),
+                self.resolver.module().into(),
                 method_name,
             )
         });
         let (receiver_ty, method_ty, substs) = match resolved {
             Some((ty, func)) => {
-                let ty = canonicalized_receiver.decanonicalize_ty(ty);
+                let ty = canonicalized_receiver.decanonicalize_ty(&mut self.table, ty);
                 let generics = generics(self.db.upcast(), func.into());
                 let substs = self.substs_for_method_call(generics, generic_args, &ty);
                 self.write_method_resolution(tgt_expr, func, substs.clone());
@@ -938,13 +1003,13 @@ fn infer_method_call(
             }
             None => (
                 receiver_ty,
-                Binders::empty(&Interner, self.err_ty()),
-                Substitution::empty(&Interner),
+                Binders::empty(Interner, self.err_ty()),
+                Substitution::empty(Interner),
             ),
         };
-        let method_ty = method_ty.substitute(&Interner, &substs);
+        let method_ty = method_ty.substitute(Interner, &substs);
         self.register_obligations_for_call(&method_ty);
-        let (expected_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
+        let (formal_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
             Some(sig) => {
                 if !sig.params().is_empty() {
                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
@@ -954,13 +1019,43 @@ fn infer_method_call(
             }
             None => (self.err_ty(), Vec::new(), self.err_ty()),
         };
-        self.unify(&expected_receiver_ty, &receiver_ty);
+        self.unify(&formal_receiver_ty, &receiver_ty);
+
+        let expected_inputs =
+            self.expected_inputs_for_expected_output(expected, ret_ty.clone(), param_tys.clone());
 
-        self.check_call_arguments(args, &param_tys);
+        self.check_call_arguments(args, &expected_inputs, &param_tys);
         self.normalize_associated_types_in(ret_ty)
     }
 
-    fn check_call_arguments(&mut self, args: &[ExprId], param_tys: &[Ty]) {
+    fn expected_inputs_for_expected_output(
+        &mut self,
+        expected_output: &Expectation,
+        output: Ty,
+        inputs: Vec<Ty>,
+    ) -> Vec<Ty> {
+        if let Some(expected_ty) = expected_output.to_option(&mut self.table) {
+            self.table.fudge_inference(|table| {
+                if table.try_unify(&expected_ty, &output).is_ok() {
+                    table.resolve_with_fallback(inputs, &|var, kind, _, _| match kind {
+                        chalk_ir::VariableKind::Ty(tk) => var.to_ty(Interner, tk).cast(Interner),
+                        chalk_ir::VariableKind::Lifetime => {
+                            var.to_lifetime(Interner).cast(Interner)
+                        }
+                        chalk_ir::VariableKind::Const(ty) => {
+                            var.to_const(Interner, ty).cast(Interner)
+                        }
+                    })
+                } else {
+                    Vec::new()
+                }
+            })
+        } else {
+            Vec::new()
+        }
+    }
+
+    fn check_call_arguments(&mut self, args: &[ExprId], expected_inputs: &[Ty], param_tys: &[Ty]) {
         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
         // We do this in a pretty awful way: first we type-check any arguments
         // that are not closures, then we type-check the closures. This is so
@@ -968,14 +1063,45 @@ fn check_call_arguments(&mut self, args: &[ExprId], param_tys: &[Ty]) {
         // type-check the functions. This isn't really the right way to do this.
         for &check_closures in &[false, true] {
             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
-            for (&arg, param_ty) in args.iter().zip(param_iter) {
+            let expected_iter = expected_inputs
+                .iter()
+                .cloned()
+                .chain(param_iter.clone().skip(expected_inputs.len()));
+            for ((&arg, param_ty), expected_ty) in args.iter().zip(param_iter).zip(expected_iter) {
                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
                 if is_closure != check_closures {
                     continue;
                 }
 
+                // the difference between param_ty and expected here is that
+                // expected is the parameter when the expected *return* type is
+                // taken into account. So in `let _: &[i32] = identity(&[1, 2])`
+                // the expected type is already `&[i32]`, whereas param_ty is
+                // still an unbound type variable. We don't always want to force
+                // the parameter to coerce to the expected type (for example in
+                // `coerce_unsize_expected_type_4`).
                 let param_ty = self.normalize_associated_types_in(param_ty);
-                self.infer_expr_coerce(arg, &Expectation::has_type(param_ty.clone()));
+                let expected = Expectation::rvalue_hint(&mut self.table, expected_ty);
+                // infer with the expected type we have...
+                let ty = self.infer_expr_inner(arg, &expected);
+
+                // then coerce to either the expected type or just the formal parameter type
+                let coercion_target = if let Some(ty) = expected.only_has_type(&mut self.table) {
+                    // if we are coercing to the expectation, unify with the
+                    // formal parameter type to connect everything
+                    self.unify(&ty, &param_ty);
+                    ty
+                } else {
+                    param_ty
+                };
+                if !coercion_target.is_unknown() {
+                    if self.coerce(Some(arg), &ty, &coercion_target).is_err() {
+                        self.result.type_mismatches.insert(
+                            arg.into(),
+                            TypeMismatch { expected: coercion_target, actual: ty.clone() },
+                        );
+                    }
+                }
             }
         }
     }
@@ -1022,27 +1148,26 @@ fn substs_for_method_call(
             substs.push(self.table.new_type_var());
         }
         assert_eq!(substs.len(), total_len);
-        Substitution::from_iter(&Interner, substs)
+        Substitution::from_iter(Interner, substs)
     }
 
     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) {
+        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());
             for predicate in generic_predicates.iter() {
                 let (predicate, binders) = predicate
                     .clone()
-                    .substitute(&Interner, parameters)
+                    .substitute(Interner, parameters)
                     .into_value_and_skipped_binders();
-                always!(binders.len(&Interner) == 0); // quantified where clauses not yet handled
-                self.push_obligation(predicate.cast(&Interner));
+                always!(binders.len(Interner) == 0); // quantified where clauses not yet handled
+                self.push_obligation(predicate.cast(Interner));
             }
             // add obligation for trait implementation, if this is a trait method
             match def {
                 CallableDefId::FunctionId(f) => {
-                    if let AssocContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container
-                    {
+                    if let ItemContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container {
                         // construct a TraitRef
                         let substs = crate::subst_prefix(
                             &*parameters,
@@ -1050,7 +1175,7 @@ fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
                         );
                         self.push_obligation(
                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
-                                .cast(&Interner),
+                                .cast(Interner),
                         );
                     }
                 }
@@ -1058,4 +1183,143 @@ fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
             }
         }
     }
+
+    fn builtin_binary_op_return_ty(&mut self, op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Option<Ty> {
+        let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
+        let rhs_ty = self.resolve_ty_shallow(&rhs_ty);
+        match op {
+            BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => {
+                Some(TyKind::Scalar(Scalar::Bool).intern(Interner))
+            }
+            BinaryOp::Assignment { .. } => Some(TyBuilder::unit()),
+            BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => {
+                // all integer combinations are valid here
+                if matches!(
+                    lhs_ty.kind(Interner),
+                    TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
+                        | TyKind::InferenceVar(_, TyVariableKind::Integer)
+                ) && matches!(
+                    rhs_ty.kind(Interner),
+                    TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
+                        | TyKind::InferenceVar(_, TyVariableKind::Integer)
+                ) {
+                    Some(lhs_ty)
+                } else {
+                    None
+                }
+            }
+            BinaryOp::ArithOp(_) => match (lhs_ty.kind(Interner), rhs_ty.kind(Interner)) {
+                // (int, int) | (uint, uint) | (float, float)
+                (TyKind::Scalar(Scalar::Int(_)), TyKind::Scalar(Scalar::Int(_)))
+                | (TyKind::Scalar(Scalar::Uint(_)), TyKind::Scalar(Scalar::Uint(_)))
+                | (TyKind::Scalar(Scalar::Float(_)), TyKind::Scalar(Scalar::Float(_))) => {
+                    Some(rhs_ty)
+                }
+                // ({int}, int) | ({int}, uint)
+                (
+                    TyKind::InferenceVar(_, TyVariableKind::Integer),
+                    TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
+                ) => Some(rhs_ty),
+                // (int, {int}) | (uint, {int})
+                (
+                    TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
+                    TyKind::InferenceVar(_, TyVariableKind::Integer),
+                ) => Some(lhs_ty),
+                // ({float} | float)
+                (
+                    TyKind::InferenceVar(_, TyVariableKind::Float),
+                    TyKind::Scalar(Scalar::Float(_)),
+                ) => Some(rhs_ty),
+                // (float, {float})
+                (
+                    TyKind::Scalar(Scalar::Float(_)),
+                    TyKind::InferenceVar(_, TyVariableKind::Float),
+                ) => Some(lhs_ty),
+                // ({int}, {int}) | ({float}, {float})
+                (
+                    TyKind::InferenceVar(_, TyVariableKind::Integer),
+                    TyKind::InferenceVar(_, TyVariableKind::Integer),
+                )
+                | (
+                    TyKind::InferenceVar(_, TyVariableKind::Float),
+                    TyKind::InferenceVar(_, TyVariableKind::Float),
+                ) => Some(rhs_ty),
+                _ => None,
+            },
+        }
+    }
+
+    fn builtin_binary_op_rhs_expectation(&mut self, op: BinaryOp, lhs_ty: Ty) -> Option<Ty> {
+        Some(match op {
+            BinaryOp::LogicOp(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
+            BinaryOp::Assignment { op: None } => lhs_ty,
+            BinaryOp::CmpOp(CmpOp::Eq { .. }) => match self
+                .resolve_ty_shallow(&lhs_ty)
+                .kind(Interner)
+            {
+                TyKind::Scalar(_) | TyKind::Str => lhs_ty,
+                TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
+                _ => return None,
+            },
+            BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => return None,
+            BinaryOp::CmpOp(CmpOp::Ord { .. })
+            | BinaryOp::Assignment { op: Some(_) }
+            | BinaryOp::ArithOp(_) => match self.resolve_ty_shallow(&lhs_ty).kind(Interner) {
+                TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_)) => lhs_ty,
+                TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
+                _ => return None,
+            },
+        })
+    }
+
+    fn resolve_binop_method(&self, op: BinaryOp) -> Option<FunctionId> {
+        let (name, lang_item) = match op {
+            BinaryOp::LogicOp(_) => return None,
+            BinaryOp::ArithOp(aop) => match aop {
+                ArithOp::Add => (name!(add), name!(add)),
+                ArithOp::Mul => (name!(mul), name!(mul)),
+                ArithOp::Sub => (name!(sub), name!(sub)),
+                ArithOp::Div => (name!(div), name!(div)),
+                ArithOp::Rem => (name!(rem), name!(rem)),
+                ArithOp::Shl => (name!(shl), name!(shl)),
+                ArithOp::Shr => (name!(shr), name!(shr)),
+                ArithOp::BitXor => (name!(bitxor), name!(bitxor)),
+                ArithOp::BitOr => (name!(bitor), name!(bitor)),
+                ArithOp::BitAnd => (name!(bitand), name!(bitand)),
+            },
+            BinaryOp::Assignment { op: Some(aop) } => match aop {
+                ArithOp::Add => (name!(add_assign), name!(add_assign)),
+                ArithOp::Mul => (name!(mul_assign), name!(mul_assign)),
+                ArithOp::Sub => (name!(sub_assign), name!(sub_assign)),
+                ArithOp::Div => (name!(div_assign), name!(div_assign)),
+                ArithOp::Rem => (name!(rem_assign), name!(rem_assign)),
+                ArithOp::Shl => (name!(shl_assign), name!(shl_assign)),
+                ArithOp::Shr => (name!(shr_assign), name!(shr_assign)),
+                ArithOp::BitXor => (name!(bitxor_assign), name!(bitxor_assign)),
+                ArithOp::BitOr => (name!(bitor_assign), name!(bitor_assign)),
+                ArithOp::BitAnd => (name!(bitand_assign), name!(bitand_assign)),
+            },
+            BinaryOp::CmpOp(cop) => match cop {
+                CmpOp::Eq { negated: false } => (name!(eq), name!(eq)),
+                CmpOp::Eq { negated: true } => (name!(ne), name!(eq)),
+                CmpOp::Ord { ordering: Ordering::Less, strict: false } => {
+                    (name!(le), name!(partial_ord))
+                }
+                CmpOp::Ord { ordering: Ordering::Less, strict: true } => {
+                    (name!(lt), name!(partial_ord))
+                }
+                CmpOp::Ord { ordering: Ordering::Greater, strict: false } => {
+                    (name!(ge), name!(partial_ord))
+                }
+                CmpOp::Ord { ordering: Ordering::Greater, strict: true } => {
+                    (name!(gt), name!(partial_ord))
+                }
+            },
+            BinaryOp::Assignment { op: None } => return None,
+        };
+
+        let trait_ = self.resolve_lang_item(lang_item)?.as_trait()?;
+
+        self.db.trait_data(trait_).method_by_name(&name)
+    }
 }