From 34fcf92ea003e401606552907516d08f1c3b94da Mon Sep 17 00:00:00 2001
From: Bryanskiy <ivakin.kir@gmail.com>
Date: Wed, 31 Jul 2024 15:55:56 +0300
Subject: [PATCH] Add special-case for [T, 0] in dropck

---
 .../src/traits/query/dropck_outlives.rs       | 11 +++++++--
 tests/ui/dropck/dropck-empty-array.rs         | 23 +++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)
 create mode 100644 tests/ui/dropck/dropck-empty-array.rs

diff --git a/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs b/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
index 37a16a43acdeb..d3a1ed52d2e62 100644
--- a/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
@@ -42,8 +42,15 @@ pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
         | ty::Foreign(..)
         | ty::Error(_) => true,
 
-        // `T is PAT`, `[T; N]`, and `[T]` have same properties as T.
-        ty::Pat(ty, _) | ty::Array(ty, _) | ty::Slice(ty) => trivial_dropck_outlives(tcx, *ty),
+        // `T is PAT` and `[T]` have same properties as T.
+        ty::Pat(ty, _) | ty::Slice(ty) => trivial_dropck_outlives(tcx, *ty),
+        ty::Array(ty, size) => {
+            // Empty array never has a dtor. See issue #110288.
+            match size.try_to_target_usize(tcx) {
+                Some(0) => true,
+                _ => trivial_dropck_outlives(tcx, *ty),
+            }
+        }
 
         // (T1..Tn) and closures have same properties as T1..Tn --
         // check if *all* of them are trivial.
diff --git a/tests/ui/dropck/dropck-empty-array.rs b/tests/ui/dropck/dropck-empty-array.rs
new file mode 100644
index 0000000000000..f3eca6aed8d5e
--- /dev/null
+++ b/tests/ui/dropck/dropck-empty-array.rs
@@ -0,0 +1,23 @@
+//@ run-pass
+
+#[allow(dead_code)]
+struct Struct<'s>(&'s str);
+
+impl<'s> Drop for Struct<'s> {
+    fn drop(&mut self) {}
+}
+
+fn to_array_zero<T>(_: T) -> [T; 0] {
+    []
+}
+
+pub fn array_zero_in_tuple() {
+    let mut x = ([], String::new());
+    {
+        let s = String::from("temporary");
+        let p = Struct(&s);
+        x.0 = to_array_zero(p);
+    }
+}
+
+fn main() {}