From a7c145fb1b3ff44ed5318b4997228301c9c6b783 Mon Sep 17 00:00:00 2001
From: Jakob Jungreuthmayer <116195279+jakobjung10@users.noreply.github.com>
Date: Sun, 12 Jul 2026 01:12:36 +0200
Subject: [PATCH] fix(emit): wrap no_mangle-family attrs as unsafe for
 edition-2024 round-trip

When the generated crate is pretty-printed and recompiled at the 2024 edition,
bare `#[no_mangle]` / `#[export_name]` / `#[link_section]` attributes are
rejected. Macros expanded from earlier-edition dependencies can emit the bare
form, which broke recompilation of the mutant crate.

In the macro-expansion sanitizer, rewrite these attributes to the
`#[unsafe(...)]` form when the session edition is 2024 or later.
---
 mutest-emit/src/codegen/hygiene.rs | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/mutest-emit/src/codegen/hygiene.rs b/mutest-emit/src/codegen/hygiene.rs
index d3efe787..cf6bcb3e 100644
--- a/mutest-emit/src/codegen/hygiene.rs
+++ b/mutest-emit/src/codegen/hygiene.rs
@@ -1514,7 +1514,19 @@ impl<'tcx, 'op> ast::mut_visit::MutVisitor for MacroExpansionSanitizer<'tcx, 'op
         if is_macro_helper_attr(&self.syntax_extensions, attr) {
             // Disable attribute by overriding it with an empty doc-comment.
             // This is easier than modifying every visit function to properly remove the attribute nodes.
-            attr.kind = ast::AttrKind::DocComment(ast::token::CommentKind::Line, sym::empty)
+            attr.kind = ast::AttrKind::DocComment(ast::token::CommentKind::Line, sym::empty);
+            return;
+        }
+
+        // In Rust 2024 `no_mangle`/`export_name`/`link_section` must be written as `unsafe(...)`.
+        // Macros from earlier-edition crates can emit the bare form, which is invalid once the
+        // generated crate is recompiled at the 2024 edition; wrap it to keep the round-trip valid.
+        if self.tcx.sess.edition().at_least_rust_2024()
+            && (attr.has_name(sym::no_mangle) || attr.has_name(sym::export_name) || attr.has_name(sym::link_section))
+            && let ast::AttrKind::Normal(normal) = &mut attr.kind
+            && let ast::Safety::Default = normal.item.unsafety
+        {
+            normal.item.unsafety = ast::Safety::Unsafe(DUMMY_SP);
         }
     }