fix couple of clippy findings:

filter_map_identity
iter_kv_map
needless_question_mark
redundant_at_rest_pattern
filter_next
derivable_impls

compiler/rustc_builtin_macros/src/asm.rs

@@ -401,7 +401,7 @@ fn parse_clobber_abi<'a>(p: &mut Parser<'a>, args: &mut AsmArgs) -> PResult<'a,
         // should have errored above during parsing
         [] => unreachable!(),
         [(abi, _span)] => args.clobber_abis.push((*abi, full_span)),
-        [abis @ ..] => {
+        abis => {
             for (abi, span) in abis {
                 args.clobber_abis.push((*abi, *span));
             }

compiler/rustc_parse/src/parser/generics.rs

@@ -49,7 +49,7 @@ impl<'a> Parser<'a> {
             && self.check_ident()
         // `Const` followed by IDENT
         {
-            return Ok(self.recover_const_param_with_mistyped_const(preceding_attrs, ident)?);
+            return self.recover_const_param_with_mistyped_const(preceding_attrs, ident);
         }
 
         // Parse optional colon and param bounds.

compiler/rustc_query_impl/src/plumbing.rs

@@ -183,7 +183,7 @@ pub(super) fn encode_all_query_results<'tcx>(
     encoder: &mut CacheEncoder<'_, 'tcx>,
     query_result_index: &mut EncodedDepNodeIndex,
 ) {
-    for encode in super::ENCODE_QUERY_RESULTS.iter().copied().filter_map(|e| e) {
+    for encode in super::ENCODE_QUERY_RESULTS.iter().copied().flatten() {
         encode(tcx, encoder, query_result_index);
     }
 }

compiler/rustc_session/src/code_stats.rs

@@ -227,10 +227,8 @@ impl CodeStats {
     }
 
     pub fn print_vtable_sizes(&self, crate_name: &str) {
-        let mut infos = std::mem::take(&mut *self.vtable_sizes.lock())
-            .into_iter()
-            .map(|(_did, stats)| stats)
-            .collect::<Vec<_>>();
+        let mut infos =
+            std::mem::take(&mut *self.vtable_sizes.lock()).into_values().collect::<Vec<_>>();
 
         // Primary sort: cost % in reverse order (from largest to smallest)
         // Secondary sort: trait_name

compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs

@@ -329,18 +329,13 @@ pub struct OnUnimplementedNote {
 }
 
 /// Append a message for `~const Trait` errors.
-#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
 pub enum AppendConstMessage {
+    #[default]
     Default,
     Custom(Symbol),
 }
 
-impl Default for AppendConstMessage {
-    fn default() -> Self {
-        AppendConstMessage::Default
-    }
-}
-
 impl<'tcx> OnUnimplementedDirective {
     fn parse(
         tcx: TyCtxt<'tcx>,

library/test/src/lib.rs

@@ -183,8 +183,7 @@ pub fn test_main_static_abort(tests: &[&TestDescAndFn]) {
 
         let test = tests
             .into_iter()
-            .filter(|test| test.desc.name.as_slice() == name)
-            .next()
+            .find(|test| test.desc.name.as_slice() == name)
             .unwrap_or_else(|| panic!("couldn't find a test with the provided name '{name}'"));
         let TestDescAndFn { desc, testfn } = test;
         match testfn.into_runnable() {