Fixed crash

Author: jagunter

compiler/rustc_hir_typeck/src/demand.rs

@@ -799,17 +799,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Detect the following case
     ///
     /// ```text
-    /// fn change_object(mut a: &Ty) {
+    /// fn change_object(mut b: &Ty) {
     ///     let a = Ty::new();
     ///     b = a;
     /// }
     /// ```
     ///
-    /// where the user likely meant to modify the value behind there reference, use `a` as an out
+    /// where the user likely meant to modify the value behind there reference, use `b` as an out
     /// parameter, instead of mutating the local binding. When encountering this we suggest:
     ///
     /// ```text
-    /// fn change_object(a: &'_ mut Ty) {
+    /// fn change_object(b: &'_ mut Ty) {
     ///     let a = Ty::new();
     ///     *b = a;
     /// }
@@ -823,6 +823,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if let Some(TypeError::Sorts(ExpectedFound { expected, found })) = error
             && let ty::Ref(_, inner, hir::Mutability::Not) = expected.kind()
 
+            // Cannot use found in can_eq if it contains region variables that no longer exist.
+            // Fixes #140823
+            && !found.has_infer_regions()
+
             // The difference between the expected and found values is one level of borrowing.
             && self.can_eq(self.param_env, *inner, found)