only emit pointer-like metadata for BZST-allocator Box

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -617,7 +617,9 @@ pub fn type_metadata<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, t: Ty<'tcx>) -> &'ll
         ty::RawPtr(ty::TypeAndMut { ty: pointee_type, .. }) | ty::Ref(_, pointee_type, _) => {
             pointer_or_reference_metadata(cx, t, pointee_type, unique_type_id)
         }
-        ty::Adt(def, _) if def.is_box() => {
+        // Box<T, A> may have a non-ZST allocator A. In that case, we
+        // cannot treat Box<T, A> as just an owned alias of `*mut T`.
+        ty::Adt(def, substs) if def.is_box() && cx.layout_of(substs.type_at(1)).is_zst() => {
             pointer_or_reference_metadata(cx, t, t.boxed_ty(), unique_type_id)
         }
         ty::FnDef(..) | ty::FnPtr(_) => subroutine_type_metadata(cx, unique_type_id),

src/test/ui/debuginfo/debuginfo-box-with-large-allocator.rs

@@ -0,0 +1,23 @@
+// build-pass
+// compile-flags: -Cdebuginfo=2
+// fixes issue #94725
+
+#![feature(allocator_api)]
+
+use std::alloc::{AllocError, Allocator, Layout};
+use std::ptr::NonNull;
+
+struct ZST;
+
+unsafe impl Allocator for &ZST {
+    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
+        todo!()
+    }
+    unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
+        todo!()
+    }
+}
+
+fn main() {
+    let _ = Box::<i32, &ZST>::new_in(43, &ZST);
+}

src/test/ui/debuginfo/debuginfo_with_uninhabitable_field_and_unsized.rs

@@ -1,4 +1,4 @@
-// check-pass
+// build-pass
 // compile-flags: -Cdebuginfo=2
 // fixes issue #94149