Revert "rustdoc: IndexItem::{stability -> is_unstable}"

This reverts commit 5e8ebd5.

Author: GuillaumeGomez

src/librustdoc/formats/cache.rs

@@ -602,7 +602,7 @@ fn add_item_to_search_index(tcx: TyCtxt<'_>, cache: &mut Cache, item: &clean::It
         search_type,
         aliases,
         deprecation,
-        is_unstable: item.stability(tcx).map(|x| x.is_unstable()).unwrap_or(false),
+        stability: item.stability(tcx),
     };
     cache.search_index.push(index_item);
 }

src/librustdoc/html/render/mod.rs

@@ -139,7 +139,12 @@ pub(crate) struct IndexItem {
     pub(crate) search_type: Option<IndexItemFunctionType>,
     pub(crate) aliases: Box<[Symbol]>,
     pub(crate) deprecation: Option<Deprecation>,
-    pub(crate) is_unstable: bool,
+    pub(crate) stability: Option<Stability>,
+}
+impl IndexItem {
+    fn is_unstable(&self) -> bool {
+        matches!(&self.stability, Some(Stability { level: StabilityLevel::Unstable { .. }, .. }))
+    }
 }
 
 /// A type used for the search index.

src/librustdoc/html/render/search_index.rs

@@ -93,7 +93,7 @@ pub(crate) fn build_index(
                 ),
                 aliases: item.attrs.get_doc_aliases(),
                 deprecation: item.deprecation(tcx),
-                is_unstable: item.stability(tcx).is_some_and(|x| x.is_unstable()),
+                stability: item.stability(tcx),
             });
         }
     }
@@ -713,7 +713,7 @@ pub(crate) fn build_index(
                     // bitmasks always use 1-indexing for items, with 0 as the crate itself
                     deprecated.push(u32::try_from(index + 1).unwrap());
                 }
-                if item.is_unstable {
+                if item.is_unstable() {
                     unstable.push(u32::try_from(index + 1).unwrap());
                 }
             }