clippy::complexity fixes

filter_next
needless_question_mark
bind_instead_of_map
manual_find
derivable_impls
map_identity
redundant_slicing
skip_while_next
unnecessary_unwrap
needless_bool

compiler/rustc_middle/src/middle/privacy.rs

@@ -103,12 +103,7 @@ impl EffectiveVisibilities {
 
     pub fn public_at_level(&self, id: LocalDefId) -> Option<Level> {
         self.effective_vis(id).and_then(|effective_vis| {
-            for level in Level::all_levels() {
-                if effective_vis.is_public_at_level(level) {
-                    return Some(level);
-                }
-            }
-            None
+            Level::all_levels().into_iter().find(|&level| effective_vis.is_public_at_level(level))
         })
     }