From 30c2e26506eb672386c70ea2e4d7e0b102f86d2d Mon Sep 17 00:00:00 2001
From: Jane Losare-Lusby <jlusby42@gmail.com>
Date: Fri, 21 Nov 2025 14:08:33 -0800
Subject: [PATCH 1/2] Add test for derive helper compat collisions

---
 .../auxiliary/extra-empty-derive.rs           |  7 ++++++
 .../helper-attr-compat-collision.rs           | 23 +++++++++++++++++++
 2 files changed, 30 insertions(+)
 create mode 100644 tests/ui/proc-macro/auxiliary/extra-empty-derive.rs
 create mode 100644 tests/ui/proc-macro/helper-attr-compat-collision.rs

diff --git a/tests/ui/proc-macro/auxiliary/extra-empty-derive.rs b/tests/ui/proc-macro/auxiliary/extra-empty-derive.rs
new file mode 100644
index 0000000000000..9a89e04364d75
--- /dev/null
+++ b/tests/ui/proc-macro/auxiliary/extra-empty-derive.rs
@@ -0,0 +1,7 @@
+extern crate proc_macro;
+use proc_macro::{TokenStream, TokenTree};
+
+#[proc_macro_derive(Empty2, attributes(empty_helper))]
+pub fn empty_derive2(_: TokenStream) -> TokenStream {
+    TokenStream::new()
+}
diff --git a/tests/ui/proc-macro/helper-attr-compat-collision.rs b/tests/ui/proc-macro/helper-attr-compat-collision.rs
new file mode 100644
index 0000000000000..1ed2f4c550663
--- /dev/null
+++ b/tests/ui/proc-macro/helper-attr-compat-collision.rs
@@ -0,0 +1,23 @@
+//@ proc-macro: test-macros.rs
+//@ proc-macro: extra-empty-derive.rs
+//@ build-pass
+
+#[macro_use(Empty)]
+extern crate test_macros;
+#[macro_use(Empty2)]
+extern crate extra_empty_derive;
+
+// Testing the behavior of derive attributes with helpers that share the same name.
+//
+// Normally if the first derive below were absent the call to #[empty_helper] before it it
+// introduced by its own derive would produce a future incompat error.
+//
+// With the extra derive also introducing that attribute in advanced the warning gets supressed.
+// Demonstrates a lack of identity to helper attributes, the compiler does not track which derive
+// introduced a helper, just that a derive introduced the helper.
+#[derive(Empty)]
+#[empty_helper]
+#[derive(Empty2)]
+struct S;
+
+fn main() {}

From 7537b0bc068b021fb852e8df92c3476b61527e15 Mon Sep 17 00:00:00 2001
From: Jane Losare-Lusby <jlusby42@gmail.com>
Date: Mon, 24 Nov 2025 10:41:28 -0800
Subject: [PATCH 2/2] Update
 tests/ui/proc-macro/helper-attr-compat-collision.rs

Co-authored-by: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
---
 tests/ui/proc-macro/helper-attr-compat-collision.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/ui/proc-macro/helper-attr-compat-collision.rs b/tests/ui/proc-macro/helper-attr-compat-collision.rs
index 1ed2f4c550663..7755582c46322 100644
--- a/tests/ui/proc-macro/helper-attr-compat-collision.rs
+++ b/tests/ui/proc-macro/helper-attr-compat-collision.rs
@@ -1,6 +1,6 @@
 //@ proc-macro: test-macros.rs
 //@ proc-macro: extra-empty-derive.rs
-//@ build-pass
+//@ check-pass
 
 #[macro_use(Empty)]
 extern crate test_macros;