From afa03ab036fdc36e86306b193d017bfa9e65ea73 Mon Sep 17 00:00:00 2001
From: Shunsuke Shibayama <sbym1346@gmail.com>
Date: Thu, 3 Oct 2024 23:18:39 +0900
Subject: [PATCH] fix: type variable bug

---
 crates/erg_compiler/ty/mod.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/crates/erg_compiler/ty/mod.rs b/crates/erg_compiler/ty/mod.rs
index 284c23f3..9bad94dd 100644
--- a/crates/erg_compiler/ty/mod.rs
+++ b/crates/erg_compiler/ty/mod.rs
@@ -4172,6 +4172,12 @@ impl Type {
             Self::FreeVar(fv) if fv.is_linked() => fv.unwrap_linked().eliminate_subsup(target),
             Self::FreeVar(ref fv) if fv.constraint_is_sandwiched() => {
                 let (sub, sup) = fv.get_subsup().unwrap();
+                let sub = if sub.addr_eq(target) {
+                    Type::Never
+                } else {
+                    sub
+                };
+                let sup = if sup.addr_eq(target) { Type::Obj } else { sup };
                 let sub = sub.eliminate_subsup(target);
                 let sup = sup.eliminate_subsup(target);
                 self.update_tyvar(sub, sup, None, false);