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_ast_lowering/src/lib.rs

@@ -620,7 +620,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.impl_trait_defs = current_impl_trait_defs;
         self.impl_trait_bounds = current_impl_trait_bounds;
 
-        debug_assert!(self.children.iter().find(|(id, _)| id == &def_id).is_none());
+        debug_assert!(!self.children.iter().any(|(id, _)| id == &def_id));
         self.children.push((def_id, hir::MaybeOwner::Owner(info)));
     }
 

compiler/rustc_borrowck/src/lib.rs

@@ -2059,12 +2059,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
     ) -> Option<InitIndex> {
         let mpi = self.move_data.rev_lookup.find_local(local);
         let ii = &self.move_data.init_path_map[mpi];
-        for &index in ii {
-            if flow_state.ever_inits.contains(index) {
-                return Some(index);
-            }
-        }
-        None
+        ii.into_iter().find(|&&index| flow_state.ever_inits.contains(index)).copied()
     }
 
     /// Adds the place into the used mutable variables set

compiler/rustc_codegen_llvm/src/builder.rs

@@ -233,8 +233,8 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         // Set KCFI operand bundle
         let is_indirect_call = unsafe { llvm::LLVMIsAFunction(llfn).is_none() };
         let kcfi_bundle =
-            if self.tcx.sess.is_sanitizer_kcfi_enabled() && fn_abi.is_some() && is_indirect_call {
-                let kcfi_typeid = kcfi_typeid_for_fnabi(self.tcx, fn_abi.unwrap());
+            if self.tcx.sess.is_sanitizer_kcfi_enabled() && let Some(fn_abi) = fn_abi && is_indirect_call {
+                let kcfi_typeid = kcfi_typeid_for_fnabi(self.tcx, fn_abi);
                 Some(llvm::OperandBundleDef::new("kcfi", &[self.const_u32(kcfi_typeid)]))
             } else {
                 None

compiler/rustc_codegen_ssa/src/back/archive.rs

@@ -123,7 +123,7 @@ fn try_filter_fat_archs<'a>(
 ) -> io::Result<Option<(&'a [u8], u64)>> {
     let archs = archs.map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
 
-    let desired = match archs.iter().filter(|a| a.architecture() == target_arch).next() {
+    let desired = match archs.iter().find(|a| a.architecture() == target_arch) {
         Some(a) => a,
         None => return Ok(None),
     };

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -1128,9 +1128,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         let hir = self.tcx.hir();
-        let cond_parent = hir.parent_iter(expr.hir_id).skip_while(|(_, node)| {
-            matches!(node, hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Binary(op, _, _), .. }) if op.node == hir::BinOpKind::And)
-        }).next();
+        let cond_parent = hir.parent_iter(expr.hir_id).find(|(_, node)| {
+            !matches!(node, hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Binary(op, _, _), .. }) if op.node == hir::BinOpKind::And)
+        });
         // Don't suggest:
         //     `let Some(_) = a.is_some() && b`
         //                     ++++++++++

compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs

@@ -488,7 +488,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                         // If this empty region is from a universe that can
                         // name the placeholder, then the placeholder is
                         // larger; otherwise, the only ancestor is `'static`.
-                        if a_ui.can_name(placeholder.universe) { true } else { false }
+                        return a_ui.can_name(placeholder.universe);
                     }
                 }
             }

compiler/rustc_infer/src/infer/undo_log.rs

@@ -87,18 +87,12 @@ impl<'tcx> Rollback<UndoLog<'tcx>> for InferCtxtInner<'tcx> {
 
 /// The combined undo log for all the various unification tables. For each change to the storage
 /// for any kind of inference variable, we record an UndoLog entry in the vector here.
-#[derive(Clone)]
+#[derive(Clone, Default)]
 pub(crate) struct InferCtxtUndoLogs<'tcx> {
     logs: Vec<UndoLog<'tcx>>,
     num_open_snapshots: usize,
 }
 
-impl Default for InferCtxtUndoLogs<'_> {
-    fn default() -> Self {
-        Self { logs: Default::default(), num_open_snapshots: Default::default() }
-    }
-}
-
 /// The UndoLogs trait defines how we undo a particular kind of action (of type T). We can undo any
 /// action that is convertible into an UndoLog (per the From impls above).
 impl<'tcx, T> UndoLogs<T> for InferCtxtUndoLogs<'tcx>

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))
         })
     }
 

compiler/rustc_mir_transform/src/sroa.rs

@@ -182,7 +182,7 @@ fn replace_flattened_locals<'tcx>(
     let mut fragments = IndexVec::new();
     for (k, v) in &replacements.fields {
         fragments.ensure_contains_elem(k.local, || Vec::new());
-        fragments[k.local].push((&k.projection[..], *v));
+        fragments[k.local].push((k.projection, *v));
     }
     debug!(?fragments);
 

compiler/rustc_monomorphize/src/collector.rs

@@ -595,8 +595,8 @@ fn check_recursion_limit<'tcx>(
         let def_path_str = tcx.def_path_str(def_id);
         let (shrunk, written_to_path) = shrunk_instance_name(tcx, &instance);
         let mut path = PathBuf::new();
-        let was_written = if written_to_path.is_some() {
-            path = written_to_path.unwrap();
+        let was_written = if let Some(written_to_path) = written_to_path {
+            path = written_to_path;
             Some(())
         } else {
             None

compiler/rustc_parse/src/parser/path.rs

@@ -277,8 +277,7 @@ impl<'a> Parser<'a> {
                         if let Some(arg) = args
                             .iter()
                             .rev()
-                            .skip_while(|arg| matches!(arg, AngleBracketedArg::Constraint(_)))
-                            .next()
+                            .find(|arg| !matches!(arg, AngleBracketedArg::Constraint(_)))
                         {
                             err.span_suggestion_verbose(
                                 arg.span().shrink_to_hi(),

compiler/rustc_passes/src/dead.rs

@@ -787,7 +787,6 @@ impl<'tcx> DeadVisitor<'tcx> {
         let mut dead_codes = dead_codes
             .iter()
             .filter(|v| !v.name.as_str().starts_with('_'))
-            .map(|v| v)
             .collect::<Vec<&DeadVariant>>();
         if dead_codes.is_empty() {
             return;

compiler/rustc_session/src/filesearch.rs

@@ -122,7 +122,7 @@ pub fn sysroot_candidates() -> SmallVec<[PathBuf; 2]> {
     let target = crate::config::host_triple();
     let mut sysroot_candidates: SmallVec<[PathBuf; 2]> =
         smallvec![get_or_default_sysroot().expect("Failed finding sysroot")];
-    let path = current_dll_path().and_then(|s| Ok(s.canonicalize().map_err(|e| e.to_string())?));
+    let path = current_dll_path().and_then(|s| s.canonicalize().map_err(|e| e.to_string()));
     if let Ok(dll) = path {
         // use `parent` twice to chop off the file name and then also the
         // directory containing the dll which should be either `lib` or `bin`.
@@ -165,7 +165,7 @@ pub fn get_or_default_sysroot() -> Result<PathBuf, String> {
     }
 
     fn default_from_rustc_driver_dll() -> Result<PathBuf, String> {
-        let dll = current_dll_path().and_then(|s| Ok(canonicalize(s)))?;
+        let dll = current_dll_path().map(|s| canonicalize(s))?;
 
         // `dll` will be in one of the following two:
         // - compiler's libdir: $sysroot/lib/*.dll

compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs

@@ -99,13 +99,8 @@ fn is_c_void_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
         ty::Adt(adt_def, ..) => {
             let def_id = adt_def.0.did;
             let crate_name = tcx.crate_name(def_id.krate);
-            if tcx.item_name(def_id).as_str() == "c_void"
+            tcx.item_name(def_id).as_str() == "c_void"
                 && (crate_name == sym::core || crate_name == sym::std || crate_name == sym::libc)
-            {
-                true
-            } else {
-                false
-            }
         }
         _ => false,
     }
@@ -267,8 +262,7 @@ fn encode_predicates<'tcx>(
 ) -> String {
     // <predicate1[..predicateN]>E as part of vendor extended type
     let mut s = String::new();
-    let predicates: Vec<ty::PolyExistentialPredicate<'tcx>> =
-        predicates.iter().map(|predicate| predicate).collect();
+    let predicates: Vec<ty::PolyExistentialPredicate<'tcx>> = predicates.iter().collect();
     for predicate in predicates {
         s.push_str(&encode_predicate(tcx, predicate, dict, options));
     }
@@ -322,7 +316,7 @@ fn encode_substs<'tcx>(
 ) -> String {
     // [I<subst1..substN>E] as part of vendor extended type
     let mut s = String::new();
-    let substs: Vec<GenericArg<'_>> = substs.iter().map(|subst| subst).collect();
+    let substs: Vec<GenericArg<'_>> = substs.iter().collect();
     if !substs.is_empty() {
         s.push('I');
         for subst in substs {
@@ -703,11 +697,8 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
                         tcx.layout_of(param_env.and(ty)).map_or(false, |layout| layout.is_zst());
                     !is_zst
                 });
-                if field.is_none() {
-                    // Transform repr(transparent) types without non-ZST field into ()
-                    ty = tcx.mk_unit();
-                } else {
-                    let ty0 = tcx.type_of(field.unwrap().did);
+                if let Some(field) = field {
+                    let ty0 = tcx.type_of(field.did);
                     // Generalize any repr(transparent) user-defined type that is either a pointer
                     // or reference, and either references itself or any other type that contains or
                     // references itself, to avoid a reference cycle.
@@ -720,6 +711,9 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
                     } else {
                         ty = transform_ty(tcx, ty0, options);
                     }
+                } else {
+                    // Transform repr(transparent) types without non-ZST field into ()
+                    ty = tcx.mk_unit();
                 }
             } else {
                 ty = tcx.mk_adt(*adt_def, transform_substs(tcx, substs, options));

compiler/rustc_transmute/src/maybe_transmutable/query_context.rs

@@ -76,11 +76,7 @@ mod rustc {
                 }
             };
 
-            let ret = if self.visibility(def_id).is_accessible_from(parent, *self) {
-                true
-            } else {
-                false
-            };
+            let ret: bool = self.visibility(def_id).is_accessible_from(parent, *self);
 
             trace!(?ret, "ret");
             ret