Handle coercion on binary operator RHS

Author: lnicola

crates/hir_ty/src/infer/expr.rs

@@ -679,7 +679,8 @@ impl<'a> InferenceContext<'a> {
                     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.infer_expr_coerce(*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());

crates/hir_ty/src/tests/coercion.rs

@@ -257,6 +257,24 @@ fn foo() {
     );
 }
 
+#[test]
+fn assign_coerce() {
+    check_no_mismatches(
+        r"
+//- minicore: deref
+struct String;
+impl core::ops::Deref for String { type Target = str; }
+fn g(_text: &str) {}
+fn f(text: &str) {
+    let mut text = text;
+    let tmp = String;
+    text = &tmp;
+    g(text);
+}
+",
+    );
+}
+
 #[test]
 fn coerce_fn_item_to_fn_ptr() {
     check_no_mismatches(