check redundant prelude imports

detects unnecessary imports in std::prelude that can be eliminated.

For example import:

```rust
use std::{option::{Iter, IterMut, IntoIter, Option::{self, Some}}, convert::{TryFrom, TryInto}, mem::drop};
```

delete : `Option::{self, Some}`  and `mem::drop`

Author: surechen

compiler/rustc_ast/src/mut_visit.rs

@@ -7,10 +7,10 @@
 //! a `MutVisitor` renaming item names in a module will miss all of those
 //! that are created by the expansion of a macro.
 
+use crate::ast::*;
 use crate::ptr::P;
 use crate::token::{self, Token};
 use crate::tokenstream::*;
-use crate::{ast::*, StaticItem};
 
 use rustc_data_structures::flat_map_in_place::FlatMapInPlace;
 use rustc_data_structures::stack::ensure_sufficient_stack;

compiler/rustc_ast/src/token.rs

@@ -13,7 +13,7 @@ use rustc_macros::HashStable_Generic;
 use rustc_span::symbol::{kw, sym};
 #[allow(hidden_glob_reexports)]
 use rustc_span::symbol::{Ident, Symbol};
-use rustc_span::{self, edition::Edition, Span, DUMMY_SP};
+use rustc_span::{edition::Edition, Span, DUMMY_SP};
 use std::borrow::Cow;
 use std::fmt;
 

compiler/rustc_ast/src/visit.rs

@@ -13,7 +13,7 @@
 //! instance, a walker looking for item names in a module will miss all of
 //! those that are created by the expansion of a macro.
 
-use crate::{ast::*, StaticItem};
+use crate::ast::*;
 
 use rustc_span::symbol::Ident;
 use rustc_span::Span;

compiler/rustc_ast_lowering/src/expr.rs

@@ -7,7 +7,6 @@ use super::errors::{
 use super::ResolverAstLoweringExt;
 use super::{ImplTraitContext, LoweringContext, ParamMode, ParenthesizedGenericArgs};
 use crate::{FnDeclKind, ImplTraitPosition};
-use rustc_ast::attr;
 use rustc_ast::ptr::P as AstP;
 use rustc_ast::*;
 use rustc_data_structures::stack::ensure_sufficient_stack;

compiler/rustc_ast_lowering/src/format.rs

@@ -1,6 +1,6 @@
 use super::LoweringContext;
 use rustc_ast as ast;
-use rustc_ast::visit::{self, Visitor};
+use rustc_ast::visit::Visitor;
 use rustc_ast::*;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_hir as hir;

compiler/rustc_ast_lowering/src/index.rs

@@ -2,7 +2,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sorted_map::SortedMap;
 use rustc_hir as hir;
 use rustc_hir::def_id::LocalDefId;
-use rustc_hir::intravisit::{self, Visitor};
+use rustc_hir::intravisit::Visitor;
 use rustc_hir::*;
 use rustc_index::{Idx, IndexVec};
 use rustc_middle::span_bug;

compiler/rustc_ast_lowering/src/lib.rs

@@ -46,7 +46,6 @@ extern crate tracing;
 use crate::errors::{AssocTyParentheses, AssocTyParenthesesSub, MisplacedImplTrait};
 
 use rustc_ast::ptr::P;
-use rustc_ast::visit;
 use rustc_ast::{self as ast, *};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::captures::Captures;

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -8,9 +8,9 @@
 
 use itertools::{Either, Itertools};
 use rustc_ast::ptr::P;
-use rustc_ast::visit::{self, AssocCtxt, BoundKind, FnCtxt, FnKind, Visitor};
+use rustc_ast::visit::{AssocCtxt, BoundKind, FnCtxt, FnKind, Visitor};
+use rustc_ast::walk_list;
 use rustc_ast::*;
-use rustc_ast::{walk_list, StaticItem};
 use rustc_ast_pretty::pprust::{self, State};
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_feature::Features;

compiler/rustc_borrowck/src/dataflow.rs

@@ -10,7 +10,7 @@ use rustc_middle::ty::RegionVid;
 use rustc_middle::ty::TyCtxt;
 use rustc_mir_dataflow::impls::{EverInitializedPlaces, MaybeUninitializedPlaces};
 use rustc_mir_dataflow::ResultsVisitable;
-use rustc_mir_dataflow::{self, fmt::DebugWithContext, GenKill};
+use rustc_mir_dataflow::{fmt::DebugWithContext, GenKill};
 use rustc_mir_dataflow::{Analysis, Direction, Results};
 use std::fmt;
 

compiler/rustc_borrowck/src/region_infer/graphviz.rs

@@ -8,7 +8,6 @@ use std::borrow::Cow;
 use std::io::{self, Write};
 
 use super::*;
-use crate::constraints::OutlivesConstraint;
 use rustc_graphviz as dot;
 
 impl<'tcx> RegionInferenceContext<'tcx> {

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -25,7 +25,6 @@ use rustc_infer::infer::{
 };
 use rustc_middle::mir::tcx::PlaceTy;
 use rustc_middle::mir::visit::{NonMutatingUseContext, PlaceContext, Visitor};
-use rustc_middle::mir::AssertKind;
 use rustc_middle::mir::*;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::ObligationCause;

compiler/rustc_builtin_macros/src/source_util.rs

@@ -5,11 +5,11 @@ use rustc_ast::tokenstream::TokenStream;
 use rustc_ast_pretty::pprust;
 use rustc_expand::base::{self, *};
 use rustc_expand::module::DirOwnership;
+use rustc_parse::new_parser_from_file;
 use rustc_parse::parser::{ForceCollect, Parser};
-use rustc_parse::{self, new_parser_from_file};
 use rustc_session::lint::builtin::INCOMPLETE_INCLUDE;
 use rustc_span::symbol::Symbol;
-use rustc_span::{self, Pos, Span};
+use rustc_span::{Pos, Span};
 
 use smallvec::SmallVec;
 use std::rc::Rc;

compiler/rustc_builtin_macros/src/test_harness.rs

@@ -2,7 +2,7 @@
 
 use rustc_ast as ast;
 use rustc_ast::entry::EntryPointType;
-use rustc_ast::mut_visit::{ExpectOne, *};
+use rustc_ast::mut_visit::*;
 use rustc_ast::ptr::P;
 use rustc_ast::visit::{walk_item, Visitor};
 use rustc_ast::{attr, ModKind};

compiler/rustc_codegen_llvm/src/abi.rs

@@ -15,7 +15,6 @@ use rustc_middle::ty::layout::LayoutOf;
 pub use rustc_middle::ty::layout::{FAT_PTR_ADDR, FAT_PTR_EXTRA};
 use rustc_middle::ty::Ty;
 use rustc_session::config;
-use rustc_target::abi::call::ArgAbi;
 pub use rustc_target::abi::call::*;
 use rustc_target::abi::{self, HasDataLayout, Int};
 pub use rustc_target::spec::abi::Abi;

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -35,7 +35,7 @@ use rustc_middle::ty::{
 use rustc_session::config::{self, DebugInfo, Lto};
 use rustc_span::symbol::Symbol;
 use rustc_span::FileName;
-use rustc_span::{self, FileNameDisplayPreference, SourceFile};
+use rustc_span::{FileNameDisplayPreference, SourceFile};
 use rustc_symbol_mangling::typeid_for_trait_ref;
 use rustc_target::abi::{Align, Size};
 use smallvec::smallvec;

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -32,7 +32,7 @@ use rustc_middle::ty::{self, Instance, ParamEnv, Ty, TypeVisitableExt};
 use rustc_session::config::{self, DebugInfo};
 use rustc_session::Session;
 use rustc_span::symbol::Symbol;
-use rustc_span::{self, BytePos, Pos, SourceFile, SourceFileAndLine, SourceFileHash, Span};
+use rustc_span::{BytePos, Pos, SourceFile, SourceFileAndLine, SourceFileHash, Span};
 use rustc_target::abi::Size;
 
 use libc::c_uint;

compiler/rustc_codegen_ssa/src/mir/statement.rs

@@ -3,7 +3,6 @@ use rustc_middle::mir::NonDivergingIntrinsic;
 
 use super::FunctionCx;
 use super::LocalRef;
-use crate::traits::BuilderMethods;
 use crate::traits::*;
 
 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -12,7 +12,7 @@ use rustc_middle::traits::BuiltinImplSource;
 use rustc_middle::ty::GenericArgs;
 use rustc_middle::ty::{self, adjustment::PointerCoercion, Instance, InstanceDef, Ty, TyCtxt};
 use rustc_middle::ty::{TraitRef, TypeVisitableExt};
-use rustc_mir_dataflow::{self, Analysis};
+use rustc_mir_dataflow::Analysis;
 use rustc_span::{sym, Span, Symbol};
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
 use rustc_trait_selection::traits::{self, ObligationCauseCode, ObligationCtxt, SelectionContext};

compiler/rustc_data_structures/src/owned_slice.rs

@@ -4,6 +4,7 @@ use crate::sync::Lrc;
 // Use our fake Send/Sync traits when on not parallel compiler,
 // so that `OwnedSlice` only implements/requires Send/Sync
 // for parallel compiler builds.
+#[allow(unused_imports)]
 use crate::sync::{Send, Sync};
 
 /// An owned slice.

compiler/rustc_expand/src/base.rs

@@ -21,7 +21,7 @@ use rustc_errors::{
 use rustc_feature::Features;
 use rustc_lint_defs::builtin::PROC_MACRO_BACK_COMPAT;
 use rustc_lint_defs::{BufferedEarlyLint, BuiltinLintDiagnostics, RegisteredTools};
-use rustc_parse::{self, parser, MACRO_ARGUMENTS};
+use rustc_parse::{parser, MACRO_ARGUMENTS};
 use rustc_session::errors::report_lit_error;
 use rustc_session::{parse::ParseSess, Limit, Session};
 use rustc_span::def_id::{CrateNum, DefId, LocalDefId};

compiler/rustc_hir_analysis/src/check/check.rs

@@ -1,5 +1,5 @@
 use crate::check::intrinsicck::InlineAsmCtxt;
-use crate::errors::{self, LinkageType};
+use crate::errors::LinkageType;
 
 use super::compare_impl_item::check_type_bounds;
 use super::compare_impl_item::{compare_impl_method, compare_impl_ty};
@@ -8,9 +8,8 @@ use rustc_attr as attr;
 use rustc_errors::{ErrorGuaranteed, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind};
-use rustc_hir::def_id::{DefId, LocalDefId, LocalModDefId};
+use rustc_hir::def_id::LocalModDefId;
 use rustc_hir::Node;
-use rustc_infer::infer::outlives::env::OutlivesEnvironment;
 use rustc_infer::infer::{RegionVariableOrigin, TyCtxtInferExt};
 use rustc_infer::traits::{Obligation, TraitEngineExt as _};
 use rustc_lint_defs::builtin::REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS;
@@ -21,18 +20,15 @@ use rustc_middle::ty::layout::{LayoutError, MAX_SIMD_LANES};
 use rustc_middle::ty::util::{Discr, IntTypeExt};
 use rustc_middle::ty::GenericArgKind;
 use rustc_middle::ty::{
-    self, AdtDef, ParamEnv, RegionKind, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable,
-    TypeVisitableExt,
+    AdtDef, ParamEnv, RegionKind, TypeSuperVisitable, TypeVisitable, TypeVisitableExt,
 };
 use rustc_session::lint::builtin::{UNINHABITED_STATIC, UNSUPPORTED_CALLING_CONVENTIONS};
 use rustc_span::symbol::sym;
-use rustc_span::{self, Span};
 use rustc_target::abi::FieldIdx;
-use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::traits::error_reporting::on_unimplemented::OnUnimplementedDirective;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
-use rustc_trait_selection::traits::{self, ObligationCtxt, TraitEngine, TraitEngineExt as _};
+use rustc_trait_selection::traits::{self, TraitEngine, TraitEngineExt as _};
 use rustc_type_ir::fold::TypeFoldable;
 
 use std::ops::ControlFlow;

compiler/rustc_hir_pretty/src/lib.rs

@@ -16,7 +16,7 @@ use rustc_hir::{BindingAnnotation, ByRef, GenericArg, GenericParam, GenericParam
 use rustc_hir::{GenericBound, PatKind, RangeEnd, TraitBoundModifier};
 use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::{kw, Ident, Symbol};
-use rustc_span::{self, FileName};
+use rustc_span::FileName;
 use rustc_target::spec::abi::Abi;
 
 use std::cell::Cell;

compiler/rustc_hir_typeck/src/coercion.rs

@@ -57,7 +57,7 @@ use rustc_middle::ty::GenericArgsRef;
 use rustc_middle::ty::{self, Ty, TypeAndMut};
 use rustc_session::parse::feature_err;
 use rustc_span::symbol::sym;
-use rustc_span::{self, DesugaringKind};
+use rustc_span::DesugaringKind;
 use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::infer::InferCtxtExt as _;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;

compiler/rustc_hir_typeck/src/diverges.rs

@@ -1,4 +1,4 @@
-use rustc_span::{self, Span, DUMMY_SP};
+use rustc_span::{Span, DUMMY_SP};
 use std::{cmp, ops};
 
 /// Tracks whether executing a node may exit normally (versus

compiler/rustc_hir_typeck/src/expectation.rs

@@ -1,6 +1,6 @@
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_middle::ty::{self, Ty};
-use rustc_span::{self, Span};
+use rustc_span::Span;
 
 use super::Expectation::*;
 use super::FnCtxt;

compiler/rustc_hir_typeck/src/fn_ctxt/adjust_fulfillment_errors.rs

@@ -4,7 +4,7 @@ use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::DefId;
 use rustc_infer::{infer::type_variable::TypeVariableOriginKind, traits::ObligationCauseCode};
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor};
-use rustc_span::{self, symbol::kw, Span};
+use rustc_span::{symbol::kw, Span};
 use rustc_trait_selection::traits;
 
 use std::ops::ControlFlow;

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -33,7 +33,7 @@ use rustc_middle::ty::visit::TypeVisitableExt;
 use rustc_middle::ty::{self, IsSuggestable, Ty, TyCtxt};
 use rustc_session::Session;
 use rustc_span::symbol::{kw, Ident};
-use rustc_span::{self, sym, BytePos, Span};
+use rustc_span::{sym, BytePos, Span};
 use rustc_trait_selection::traits::{self, ObligationCauseCode, SelectionContext};
 
 use std::iter;

compiler/rustc_hir_typeck/src/inherited.rs

@@ -9,7 +9,7 @@ use rustc_middle::traits::DefiningAnchor;
 use rustc_middle::ty::visit::TypeVisitableExt;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::def_id::LocalDefIdMap;
-use rustc_span::{self, Span};
+use rustc_span::Span;
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
 use rustc_trait_selection::traits::{self, PredicateObligation, TraitEngine, TraitEngineExt as _};
 

compiler/rustc_hir_typeck/src/op.rs

@@ -4,7 +4,7 @@ use super::method::MethodCallee;
 use super::{has_expected_num_generic_args, FnCtxt};
 use crate::Expectation;
 use rustc_ast as ast;
-use rustc_errors::{self, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder};
+use rustc_errors::{struct_span_err, Applicability, Diagnostic, DiagnosticBuilder};
 use rustc_hir as hir;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::traits::ObligationCauseCode;

compiler/rustc_incremental/src/persist/dirty_clean.rs

@@ -32,7 +32,6 @@ use rustc_middle::hir::nested_filter;
 use rustc_middle::ty::TyCtxt;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::Span;
-use std::iter::FromIterator;
 use thin_vec::ThinVec;
 
 const LOADED_FROM_DISK: Symbol = sym::loaded_from_disk;

compiler/rustc_infer/src/errors/note_and_explain.rs

@@ -1,6 +1,6 @@
 use crate::fluent_generated as fluent;
 use crate::infer::error_reporting::nice_region_error::find_anon_type;
-use rustc_errors::{self, AddToDiagnostic, Diagnostic, IntoDiagnosticArg, SubdiagnosticMessage};
+use rustc_errors::{AddToDiagnostic, Diagnostic, IntoDiagnosticArg, SubdiagnosticMessage};
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::{symbol::kw, Span};
 

compiler/rustc_interface/src/passes.rs

@@ -22,7 +22,7 @@ use rustc_middle::ty::{self, GlobalCtxt, RegisteredTools, TyCtxt};
 use rustc_middle::util::Providers;
 use rustc_mir_build as mir_build;
 use rustc_parse::{parse_crate_from_file, parse_crate_from_source_str, validate_attr};
-use rustc_passes::{self, abi_test, hir_stats, layout_test};
+use rustc_passes::{abi_test, hir_stats, layout_test};
 use rustc_resolve::Resolver;
 use rustc_session::code_stats::VTableSizeInfo;
 use rustc_session::config::{CrateType, Input, OutFileName, OutputFilenames, OutputType};

compiler/rustc_lint/src/builtin.rs

@@ -40,7 +40,6 @@ use crate::{
     },
     EarlyContext, EarlyLintPass, LateContext, LateLintPass, Level, LintContext,
 };
-use rustc_ast::attr;
 use rustc_ast::tokenstream::{TokenStream, TokenTree};
 use rustc_ast::visit::{FnCtxt, FnKind};
 use rustc_ast::{self as ast, *};

compiler/rustc_lint/src/lib.rs

@@ -94,9 +94,6 @@ pub use array_into_iter::ARRAY_INTO_ITER;
 use rustc_hir::def_id::LocalModDefId;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::TyCtxt;
-use rustc_session::lint::builtin::{
-    BARE_TRAIT_OBJECTS, ELIDED_LIFETIMES_IN_PATHS, EXPLICIT_OUTLIVES_REQUIREMENTS,
-};
 
 use array_into_iter::ArrayIntoIter;
 use async_fn_in_trait::AsyncFnInTrait;

compiler/rustc_macros/src/hash_stable.rs

@@ -1,6 +1,6 @@
-use proc_macro2::{self, Ident};
+use proc_macro2::Ident;
 use quote::quote;
-use syn::{self, parse_quote};
+use syn::parse_quote;
 
 struct Attributes {
     ignore: bool,

compiler/rustc_macros/src/lift.rs

@@ -1,5 +1,5 @@
 use quote::quote;
-use syn::{self, parse_quote};
+use syn::parse_quote;
 
 pub fn lift_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
     s.add_bounds(synstructure::AddBounds::Generics);