From 534c6baf8b7a5c74bbd6356f85182530bbb4a125 Mon Sep 17 00:00:00 2001
From: Aaron Feickert <66188213+AaronFeickert@users.noreply.github.com>
Date: Fri, 5 Jul 2024 09:15:13 -0500
Subject: [PATCH] Add a marker trait for equality testing

---
 src/lib.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/lib.rs b/src/lib.rs
index 9fc143b..21b4159 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -286,6 +286,16 @@ pub trait ConstantTimeEq {
     }
 }
 
+/// A marker trait indicating that `Eq` equality testing uses `ConstantTimeEq` under the hood.
+/// 
+/// Even though `Eq`-based equality testing returns a `bool`, it's a common design pattern
+/// to have some types implement this using `ConstantTimeEq`, and then coerce the resulting
+/// `Choice` into a `bool`.
+/// 
+/// This marker trait should be used if and only if you do this, in order to signal this
+/// functionality to implementers.
+pub trait EqIsConstantTimeEq {}
+
 impl<T: ConstantTimeEq> ConstantTimeEq for [T] {
     /// Check whether two slices of `ConstantTimeEq` types are equal.
     ///