From a1b03e30675fcf1fadd9979f6c10a10182c7660e Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Thu, 30 Nov 2023 17:01:28 +0100
Subject: [PATCH] explain a good reason for why LocalValue does not store the
 type of the local

---
 compiler/rustc_const_eval/src/interpret/eval_context.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index 3bdfc1db913a4..32220b2aa7635 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -173,6 +173,9 @@ impl<Prov: Provenance> std::fmt::Debug for LocalState<'_, Prov> {
 }
 
 /// Current value of a local variable
+///
+/// This does not store the type of the local; the type is given by `body.local_decls` and can never
+/// change, so by not storing here we avoid having to maintain that as an invariant.
 #[derive(Copy, Clone, Debug)] // Miri debug-prints these
 pub(super) enum LocalValue<Prov: Provenance = AllocId> {
     /// This local is not currently alive, and cannot be used at all.