Fix clippy and rustdoc

please, please, don't match on `Symbol::as_str`s, every time you do,
somewhere in the world another waffle becomes sad...

compiler/rustc_span/src/symbol.rs

@@ -542,6 +542,7 @@ symbols! {
         core,
         core_panic,
         core_panic_2015_macro,
+        core_panic_2021_macro,
         core_panic_macro,
         cosf32,
         cosf64,
@@ -621,6 +622,7 @@ symbols! {
         doc_primitive,
         doc_spotlight,
         doctest,
+        document_private_items,
         dotdot: "..",
         dotdot_in_tuple_patterns,
         dotdoteq_in_patterns,

library/core/src/panic.rs

@@ -43,6 +43,7 @@ pub macro panic_2015 {
 #[doc(hidden)]
 #[unstable(feature = "edition_panic", issue = "none", reason = "use panic!() instead")]
 #[allow_internal_unstable(core_panic, const_format_args)]
+#[rustc_diagnostic_item = "core_panic_2021_macro"]
 #[rustc_macro_transparency = "semitransparent"]
 pub macro panic_2021 {
     () => (

src/tools/clippy/clippy_utils/src/macros.rs

@@ -199,12 +199,12 @@ pub fn first_node_in_macro(cx: &LateContext<'_>, node: &impl HirNode) -> Option<
 pub fn is_panic(cx: &LateContext<'_>, def_id: DefId) -> bool {
     let Some(name) = cx.tcx.get_diagnostic_name(def_id) else { return false };
     matches!(
-        name.as_str(),
-        "core_panic_macro"
-            | "std_panic_macro"
-            | "core_panic_2015_macro"
-            | "std_panic_2015_macro"
-            | "core_panic_2021_macro"
+        name,
+        sym::core_panic_macro
+            | sym::std_panic_macro
+            | sym::core_panic_2015_macro
+            | sym::std_panic_2015_macro
+            | sym::core_panic_2021_macro
     )
 }