From 061b906683eccd01b59f848a7941f3fd7aff8b00 Mon Sep 17 00:00:00 2001
From: Dylan MacKenzie <ecstaticmorse@gmail.com>
Date: Sun, 13 Oct 2019 12:27:11 -0700
Subject: [PATCH 1/3] Return `false` from `needs_drop` for all zero-sized
 arrays

---
 src/librustc/ty/util.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/librustc/ty/util.rs b/src/librustc/ty/util.rs
index 5ddf15317a31c..b6e8b8b92e6c6 100644
--- a/src/librustc/ty/util.rs
+++ b/src/librustc/ty/util.rs
@@ -1096,6 +1096,9 @@ fn needs_drop_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>
 
         ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
 
+        // Zero-length arrays never contain anything to drop.
+        ty::Array(_, len) if len.try_eval_usize(tcx, param_env) == Some(0) => false,
+
         // Structural recursion.
         ty::Array(ty, _) | ty::Slice(ty) => needs_drop(ty),
 

From 8fd16baa57aafd4959bda052dad261da997e6862 Mon Sep 17 00:00:00 2001
From: Dylan MacKenzie <ecstaticmorse@gmail.com>
Date: Sun, 13 Oct 2019 12:27:45 -0700
Subject: [PATCH 2/3] Remove special case for zero-sized arrays from indirectly
 mut locals

---
 .../dataflow/impls/indirect_mutation.rs         | 17 ++++-------------
 1 file changed, 4 insertions(+), 13 deletions(-)

diff --git a/src/librustc_mir/dataflow/impls/indirect_mutation.rs b/src/librustc_mir/dataflow/impls/indirect_mutation.rs
index 990425c3252e0..bc09e32717926 100644
--- a/src/librustc_mir/dataflow/impls/indirect_mutation.rs
+++ b/src/librustc_mir/dataflow/impls/indirect_mutation.rs
@@ -104,25 +104,16 @@ impl<'tcx> TransferFunction<'_, '_, 'tcx> {
         kind: mir::BorrowKind,
         borrowed_place: &mir::Place<'tcx>,
     ) -> bool {
-        let borrowed_ty = borrowed_place.ty(self.body, self.tcx).ty;
-
-        // Zero-sized types cannot be mutated, since there is nothing inside to mutate.
-        //
-        // FIXME: For now, we only exempt arrays of length zero. We need to carefully
-        // consider the effects before extending this to all ZSTs.
-        if let ty::Array(_, len) = borrowed_ty.kind {
-            if len.try_eval_usize(self.tcx, self.param_env) == Some(0) {
-                return false;
-            }
-        }
-
         match kind {
             mir::BorrowKind::Mut { .. } => true,
 
             | mir::BorrowKind::Shared
             | mir::BorrowKind::Shallow
             | mir::BorrowKind::Unique
-            => !borrowed_ty.is_freeze(self.tcx, self.param_env, DUMMY_SP),
+            => !borrowed_place
+                .ty(self.body, self.tcx)
+                .ty
+                .is_freeze(self.tcx, self.param_env, DUMMY_SP),
         }
     }
 }

From c08a8713381ed67caea826a793145240cd873081 Mon Sep 17 00:00:00 2001
From: Dylan MacKenzie <ecstaticmorse@gmail.com>
Date: Sun, 13 Oct 2019 16:00:49 -0700
Subject: [PATCH 3/3] Add regression test for #65348

---
 src/test/ui/consts/issue-65348.rs | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 src/test/ui/consts/issue-65348.rs

diff --git a/src/test/ui/consts/issue-65348.rs b/src/test/ui/consts/issue-65348.rs
new file mode 100644
index 0000000000000..5eafa831d6317
--- /dev/null
+++ b/src/test/ui/consts/issue-65348.rs
@@ -0,0 +1,23 @@
+// check-pass
+
+struct Generic<T>(T);
+
+impl<T> Generic<T> {
+    const ARRAY: [T; 0] = [];
+    const NEWTYPE_ARRAY: Generic<[T; 0]> = Generic([]);
+    const ARRAY_FIELD: Generic<(i32, [T; 0])> = Generic((0, []));
+}
+
+pub const fn array<T>() ->  &'static T {
+    &Generic::<T>::ARRAY[0]
+}
+
+pub const fn newtype_array<T>() ->  &'static T {
+    &Generic::<T>::NEWTYPE_ARRAY.0[0]
+}
+
+pub const fn array_field<T>() ->  &'static T {
+    &(Generic::<T>::ARRAY_FIELD.0).1[0]
+}
+
+fn main() {}