From 2e2b687facb290645d4ea1665f0e7001f9431acc Mon Sep 17 00:00:00 2001
From: Brendan Hansknecht <brendan.hansknecht@gmail.com>
Date: Thu, 6 Apr 2023 20:41:04 -0700
Subject: [PATCH] fix errors with alias analysis

---
 crates/compiler/solve/src/solve.rs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/crates/compiler/solve/src/solve.rs b/crates/compiler/solve/src/solve.rs
index 4f6489d578..cfa7928a7c 100644
--- a/crates/compiler/solve/src/solve.rs
+++ b/crates/compiler/solve/src/solve.rs
@@ -1785,7 +1785,9 @@ fn solve(
                 );
 
                 if let Success { .. } = unify(
-                    &mut UEnv::new(subs),
+                    // TODO: if we don't clone and a later branch matches, we will get a failure in alias analysis.
+                    // That said, I assume cloning is expensive and should be avoided.
+                    &mut UEnv::new(&mut subs.clone()),
                     actual,
                     Variable::LIST_U8,
                     Mode::EQ,
@@ -1794,7 +1796,7 @@ fn solve(
                     // List U8 always valid.
                     state
                 } else if let Success { .. } = unify(
-                    &mut UEnv::new(subs),
+                    &mut UEnv::new(&mut subs.clone()),
                     actual,
                     Variable::STR,
                     Mode::EQ,