From 0ca1a94b2bd58d19a1bd492300abd5bffe5263fb Mon Sep 17 00:00:00 2001
From: Ben Kimock <kimockb@gmail.com>
Date: Wed, 8 May 2024 17:21:06 -0400
Subject: [PATCH] Handle field projections like slice indexing in
 invalid_reference_casting

---
 compiler/rustc_lint/src/reference_casting.rs | 3 ++-
 tests/ui/lint/reference_casting.rs           | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_lint/src/reference_casting.rs b/compiler/rustc_lint/src/reference_casting.rs
index 63d55a73a98..b80e90c25a3 100644
--- a/compiler/rustc_lint/src/reference_casting.rs
+++ b/compiler/rustc_lint/src/reference_casting.rs
@@ -202,7 +202,8 @@ fn is_cast_to_bigger_memory_layout<'tcx>(
 
     // if the current expr looks like this `&mut expr[index]` then just looking
     // at `expr[index]` won't give us the underlying allocation, so we just skip it
-    if let ExprKind::Index(..) = e_alloc.kind {
+    // the same logic applies field access like `&mut expr.field`
+    if let ExprKind::Index(..) | ExprKind::Field(..) = e_alloc.kind {
         return None;
     }
 
diff --git a/tests/ui/lint/reference_casting.rs b/tests/ui/lint/reference_casting.rs
index 3d0c36ca118..87a682249b0 100644
--- a/tests/ui/lint/reference_casting.rs
+++ b/tests/ui/lint/reference_casting.rs
@@ -255,6 +255,12 @@ unsafe fn slice_index(array: &mut [u8], offset: usize) {
         let a3 = a2 as *mut u64;
         unsafe { *a3 = 3 };
     }
+
+    unsafe fn field_access(v: &mut Vec3<i32>) {
+        let r = &mut v.0;
+        let ptr = r as *mut i32 as *mut Vec3<i32>;
+        unsafe { *ptr = Vec3(0, 0, 0) }
+    }
 }
 
 const RAW_PTR: *mut u8 = 1 as *mut u8;