Rollup merge of #128226 - oli-obk:option_vs_empty_slice, r=petrochenkov

Remove redundant option that was just encoding that a slice was empty

There is already a sanity check ensuring we don't put empty attribute lists into the HIR:

https://github.com/rust-lang/rust/blob/6ef11b81c2c02c3c4b7556d1991a98572fe9af87/compiler/rustc_ast_lowering/src/lib.rs#L661-L667

compiler/rustc_ast_lowering/src/item.rs

@@ -172,7 +172,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         id: NodeId,
         hir_id: hir::HirId,
         ident: &mut Ident,
-        attrs: Option<&'hir [Attribute]>,
+        attrs: &'hir [Attribute],
         vis_span: Span,
         i: &ItemKind,
     ) -> hir::ItemKind<'hir> {
@@ -488,7 +488,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         id: NodeId,
         vis_span: Span,
         ident: &mut Ident,
-        attrs: Option<&'hir [Attribute]>,
+        attrs: &'hir [Attribute],
     ) -> hir::ItemKind<'hir> {
         let path = &tree.prefix;
         let segments = prefix.segments.iter().chain(path.segments.iter()).cloned().collect();
@@ -566,7 +566,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         // `ItemLocalId` and the new owner. (See `lower_node_id`)
                         let kind =
                             this.lower_use_tree(use_tree, &prefix, id, vis_span, &mut ident, attrs);
-                        if let Some(attrs) = attrs {
+                        if !attrs.is_empty() {
                             this.attrs.insert(hir::ItemLocalId::ZERO, attrs);
                         }
 

compiler/rustc_ast_lowering/src/lib.rs

@@ -913,15 +913,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         ret
     }
 
-    fn lower_attrs(&mut self, id: HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
+    fn lower_attrs(&mut self, id: HirId, attrs: &[Attribute]) -> &'hir [Attribute] {
         if attrs.is_empty() {
-            None
+            &[]
         } else {
             debug_assert_eq!(id.owner, self.current_hir_id_owner);
             let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
             debug_assert!(!ret.is_empty());
             self.attrs.insert(id.local_id, ret);
-            Some(ret)
+            ret
         }
     }