From e500e1777ee2de537f5ca1e9dfc4bff9ddae14ed Mon Sep 17 00:00:00 2001
From: Ary Borenszweig <asterite@gmail.com>
Date: Fri, 6 Sep 2024 16:12:03 -0300
Subject: [PATCH] fix: let `derive(Eq)` work for empty structs

---
 noir_stdlib/src/cmp.nr                             | 8 +++++++-
 test_programs/execution_success/derive/src/main.nr | 6 ++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/noir_stdlib/src/cmp.nr b/noir_stdlib/src/cmp.nr
index b7f473429a7..521604a4e20 100644
--- a/noir_stdlib/src/cmp.nr
+++ b/noir_stdlib/src/cmp.nr
@@ -11,7 +11,13 @@ trait Eq {
 comptime fn derive_eq(s: StructDefinition) -> Quoted {
     let signature = quote { fn eq(_self: Self, _other: Self) -> bool };
     let for_each_field = |name| quote { (_self.$name == _other.$name) };
-    let body = |fields| fields;
+    let body = |fields| {
+        if s.fields().len() == 0 {
+            quote { true }
+        } else {
+            fields
+        }
+    };
     crate::meta::make_trait_impl(s, quote { Eq }, signature, for_each_field, quote { & }, body)
 }
 // docs:end:derive_eq
diff --git a/test_programs/execution_success/derive/src/main.nr b/test_programs/execution_success/derive/src/main.nr
index 5ec2fb32a79..b32612831d7 100644
--- a/test_programs/execution_success/derive/src/main.nr
+++ b/test_programs/execution_success/derive/src/main.nr
@@ -35,6 +35,9 @@ struct MyOtherOtherStruct<T> {
     x: T,
 }
 
+#[derive(Eq, Default, Hash, Ord)]
+struct EmptyStruct { }
+
 fn main() {
     let s = MyStruct { my_field: 1 };
     s.do_nothing();
@@ -53,6 +56,9 @@ fn main() {
     let mut hasher = TestHasher { result: 0 };
     o1.hash(&mut hasher);
     assert_eq(hasher.finish(), 12 + 24 + 54);
+
+    let empty = EmptyStruct {};
+    assert_eq(empty, empty);
 }
 
 struct TestHasher {