fix a couple clippy:complexitys

 double_parens
 filter_map_identity
 needless_question_mark
 redundant_guards

Author: matthiaskrgr

compiler/rustc_attr/src/builtin.rs

@@ -619,11 +619,11 @@ pub fn eval_condition(
                 // we can't use `try_gate_cfg` as symbols don't differentiate between `r#true`
                 // and `true`, and we want to keep the former working without feature gate
                 gate_cfg(
-                    &((
+                    &(
                         if *b { kw::True } else { kw::False },
                         sym::cfg_boolean_literals,
                         |features: &Features| features.cfg_boolean_literals(),
-                    )),
+                    ),
                     cfg.span(),
                     sess,
                     features,

compiler/rustc_middle/src/mir/pretty.rs

@@ -277,9 +277,9 @@ pub fn create_dump_file<'tcx>(
             )
         })?;
     }
-    Ok(fs::File::create_buffered(&file_path).map_err(|e| {
+    fs::File::create_buffered(&file_path).map_err(|e| {
         io::Error::new(e.kind(), format!("IO error creating MIR dump file: {file_path:?}; {e}"))
-    })?)
+    })
 }
 
 ///////////////////////////////////////////////////////////////////////////

compiler/rustc_mir_transform/src/coverage/mappings.rs

@@ -363,7 +363,7 @@ fn calc_test_vectors_index(conditions: &mut Vec<MCDCBranch>) -> usize {
             let ConditionInfo { condition_id, true_next_id, false_next_id } = branch.condition_info;
             [true_next_id, false_next_id]
                 .into_iter()
-                .filter_map(std::convert::identity)
+                .flatten()
                 .for_each(|next_id| indegree_stats[next_id] += 1);
             (condition_id, branch)
         })

compiler/rustc_mir_transform/src/coverage/spans.rs

@@ -87,7 +87,7 @@ fn remove_unwanted_expansion_spans(covspans: &mut Vec<SpanFromMir>) {
     covspans.retain(|covspan| {
         match covspan.expn_kind {
             // Retain only the first await-related or macro-expanded covspan with this span.
-            Some(ExpnKind::Desugaring(kind)) if kind == DesugaringKind::Await => {
+            Some(ExpnKind::Desugaring(DesugaringKind::Await)) => {
                 deduplicated_spans.insert(covspan.span)
             }
             Some(ExpnKind::Macro(MacroKind::Bang, _)) => deduplicated_spans.insert(covspan.span),