From fe1e324694425e9b683b72be5371a555601ffe6c Mon Sep 17 00:00:00 2001
From: Chayim Refael Friedman <chayimfr@gmail.com>
Date: Sun, 23 Jan 2022 05:59:35 +0200
Subject: [PATCH] Type-inference for `let` expressions

---
 crates/hir_ty/src/infer/expr.rs | 29 +++++++++++------------------
 1 file changed, 11 insertions(+), 18 deletions(-)

diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 4f1bdee705d..13f64d68252 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -8,10 +8,7 @@ use std::{
 
 use chalk_ir::{cast::Cast, fold::Shift, Mutability, TyVariableKind};
 use hir_def::{
-    expr::{
-        ArithOp, Array, BinaryOp, CmpOp, Expr, ExprId, Literal, MatchGuard, Ordering, Statement,
-        UnaryOp,
-    },
+    expr::{ArithOp, Array, BinaryOp, CmpOp, Expr, ExprId, Literal, Ordering, Statement, UnaryOp},
     path::{GenericArg, GenericArgs},
     resolver::resolver_for_expr,
     FieldId, FunctionId, ItemContainerId, Lookup,
@@ -158,6 +155,11 @@ impl<'a> InferenceContext<'a> {
 
                 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,
@@ -378,20 +380,11 @@ impl<'a> InferenceContext<'a> {
                 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);