compiler: remove unnecessary imports and qualified paths

compiler/rustc_abi/src/lib.rs

@@ -1,6 +1,5 @@
 #![cfg_attr(feature = "nightly", feature(step_trait, rustc_attrs, min_specialization))]
 
-use std::convert::{TryFrom, TryInto};
 use std::fmt;
 #[cfg(feature = "nightly")]
 use std::iter::Step;

compiler/rustc_apfloat/src/ieee.rs

@@ -2,7 +2,6 @@ use crate::{Category, ExpInt, IEK_INF, IEK_NAN, IEK_ZERO};
 use crate::{Float, FloatConvert, ParseError, Round, Status, StatusAnd};
 
 use core::cmp::{self, Ordering};
-use core::convert::TryFrom;
 use core::fmt::{self, Write};
 use core::marker::PhantomData;
 use core::mem;

compiler/rustc_arena/src/lib.rs

@@ -28,7 +28,7 @@ use smallvec::SmallVec;
 use std::alloc::Layout;
 use std::cell::{Cell, RefCell};
 use std::cmp;
-use std::marker::{PhantomData, Send};
+use std::marker::PhantomData;
 use std::mem::{self, MaybeUninit};
 use std::ptr::{self, NonNull};
 use std::slice;

compiler/rustc_ast/src/ast.rs

@@ -33,7 +33,6 @@ use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use rustc_span::source_map::{respan, Spanned};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
-use std::convert::TryFrom;
 use std::fmt;
 use std::mem;
 use thin_vec::{thin_vec, ThinVec};

compiler/rustc_ast/src/ptr.rs

@@ -22,7 +22,6 @@
 //!   Moreover, a switch to, e.g., `P<'a, T>` would be easy and mostly automated.
 
 use std::fmt::{self, Debug, Display};
-use std::iter::FromIterator;
 use std::ops::{Deref, DerefMut};
 use std::{slice, vec};
 

compiler/rustc_ast/src/tokenstream.rs

@@ -362,7 +362,7 @@ impl TokenStream {
     }
 }
 
-impl iter::FromIterator<TokenTree> for TokenStream {
+impl FromIterator<TokenTree> for TokenStream {
     fn from_iter<I: IntoIterator<Item = TokenTree>>(iter: I) -> Self {
         TokenStream::new(iter.into_iter().collect::<Vec<TokenTree>>())
     }

compiler/rustc_ast_lowering/src/lib.rs

@@ -456,8 +456,8 @@ pub fn lower_to_hir<'hir>(tcx: TyCtxt<'hir>, (): ()) -> hir::Crate<'hir> {
     }
 
     // Drop AST to free memory
-    std::mem::drop(ast_index);
-    sess.time("drop_ast", || std::mem::drop(krate));
+    drop(ast_index);
+    sess.time("drop_ast", || drop(krate));
 
     // Discard hygiene data, which isn't required after lowering to HIR.
     if !sess.opts.unstable_opts.keep_hygiene_data {

compiler/rustc_builtin_macros/src/concat.rs

@@ -4,8 +4,6 @@ use rustc_expand::base::{self, DummyResult};
 use rustc_session::errors::report_lit_error;
 use rustc_span::symbol::Symbol;
 
-use std::string::String;
-
 pub fn expand_concat(
     cx: &mut base::ExtCtxt<'_>,
     sp: rustc_span::Span,

compiler/rustc_codegen_ssa/src/base.rs

@@ -41,7 +41,6 @@ use rustc_span::{DebuggerVisualizerFile, DebuggerVisualizerType};
 use rustc_target::abi::{Align, Size, VariantIdx};
 
 use std::collections::BTreeSet;
-use std::convert::TryFrom;
 use std::time::{Duration, Instant};
 
 use itertools::Itertools;

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -1,5 +1,4 @@
 use std::borrow::Cow;
-use std::convert::TryInto;
 
 use either::{Left, Right};
 

compiler/rustc_const_eval/src/interpret/cast.rs

@@ -1,5 +1,4 @@
 use std::assert_matches::assert_matches;
-use std::convert::TryFrom;
 
 use rustc_apfloat::ieee::{Double, Single};
 use rustc_apfloat::{Float, FloatConvert};

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -2,8 +2,6 @@
 //! looking at their MIR. Intrinsics/functions supported here are shared by CTFE
 //! and miri.
 
-use std::convert::TryFrom;
-
 use rustc_hir::def_id::DefId;
 use rustc_middle::mir::{
     self,

compiler/rustc_const_eval/src/interpret/intrinsics/caller_location.rs

@@ -1,5 +1,3 @@
-use std::convert::TryFrom;
-
 use rustc_ast::Mutability;
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::mir::TerminatorKind;

compiler/rustc_const_eval/src/interpret/operator.rs

@@ -1,5 +1,3 @@
-use std::convert::TryFrom;
-
 use rustc_apfloat::Float;
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::{InterpResult, Scalar};

compiler/rustc_const_eval/src/interpret/util.rs

@@ -1,6 +1,5 @@
 use rustc_middle::mir::interpret::InterpResult;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor};
-use std::convert::TryInto;
 use std::ops::ControlFlow;
 
 /// Checks whether a type contains generic parameters which require substitution.

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -4,7 +4,6 @@
 //! That's useful because it means other passes (e.g. promotion) can rely on `const`s
 //! to be const-safe.
 
-use std::convert::TryFrom;
 use std::fmt::{Display, Write};
 use std::num::NonZeroUsize;
 

compiler/rustc_const_eval/src/util/aggregate.rs

@@ -3,7 +3,6 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::{Ty, TyCtxt};
 use rustc_target::abi::VariantIdx;
 
-use std::convert::TryFrom;
 use std::iter::TrustedLen;
 
 /// Expand `lhs = Rvalue::Aggregate(kind, operands)` into assignments to the fields.

compiler/rustc_data_structures/src/fingerprint.rs

@@ -1,6 +1,5 @@
 use crate::stable_hasher;
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
-use std::convert::TryInto;
 use std::hash::{Hash, Hasher};
 
 #[cfg(test)]

compiler/rustc_data_structures/src/graph/scc/mod.rs

@@ -9,7 +9,6 @@ use crate::fx::FxHashSet;
 use crate::graph::vec_graph::VecGraph;
 use crate::graph::{DirectedGraph, GraphSuccessors, WithNumEdges, WithNumNodes, WithSuccessors};
 use rustc_index::vec::{Idx, IndexVec};
-use std::cmp::Ord;
 use std::ops::Range;
 
 #[cfg(test)]

compiler/rustc_data_structures/src/graph/vec_graph/mod.rs

@@ -1,5 +1,3 @@
-use std::cmp::Ord;
-
 use crate::graph::{DirectedGraph, GraphSuccessors, WithNumEdges, WithNumNodes, WithSuccessors};
 use rustc_index::vec::{Idx, IndexVec};
 

compiler/rustc_data_structures/src/owning_ref/mod.rs

@@ -867,11 +867,9 @@ where
 /////////////////////////////////////////////////////////////////////////////
 
 use std::borrow::Borrow;
-use std::cmp::{Eq, Ord, Ordering, PartialEq, PartialOrd};
-use std::convert::From;
+use std::cmp::Ordering;
 use std::fmt::{self, Debug};
 use std::hash::{Hash, Hasher};
-use std::marker::{Send, Sync};
 
 impl<O, T: ?Sized> Deref for OwningRef<O, T> {
     type Target = T;
@@ -1096,7 +1094,6 @@ where
 // std types integration and convenience type defs
 /////////////////////////////////////////////////////////////////////////////
 
-use std::boxed::Box;
 use std::cell::{Ref, RefCell, RefMut};
 use std::rc::Rc;
 use std::sync::Arc;

compiler/rustc_data_structures/src/owning_ref/tests.rs

@@ -3,7 +3,7 @@
 mod owning_ref {
     use super::super::OwningRef;
     use super::super::{BoxRef, Erased, ErasedBoxRef, RcRef};
-    use std::cmp::{Ord, Ordering, PartialEq, PartialOrd};
+    use std::cmp::Ordering;
     use std::collections::hash_map::DefaultHasher;
     use std::collections::HashMap;
     use std::hash::{Hash, Hasher};
@@ -368,7 +368,7 @@ mod owning_handle {
 mod owning_ref_mut {
     use super::super::BoxRef;
     use super::super::{BoxRefMut, Erased, ErasedBoxRefMut, OwningRefMut};
-    use std::cmp::{Ord, Ordering, PartialEq, PartialOrd};
+    use std::cmp::Ordering;
     use std::collections::hash_map::DefaultHasher;
     use std::collections::HashMap;
     use std::hash::{Hash, Hasher};

compiler/rustc_data_structures/src/profiling.rs

@@ -86,7 +86,6 @@ use crate::fx::FxHashMap;
 
 use std::borrow::Borrow;
 use std::collections::hash_map::Entry;
-use std::convert::Into;
 use std::error::Error;
 use std::fs;
 use std::path::Path;

compiler/rustc_data_structures/src/sorted_map.rs

@@ -1,7 +1,6 @@
 use crate::stable_hasher::{HashStable, StableHasher, StableOrd};
 use std::borrow::Borrow;
 use std::cmp::Ordering;
-use std::iter::FromIterator;
 use std::mem;
 use std::ops::{Bound, Index, IndexMut, RangeBounds};
 

compiler/rustc_data_structures/src/sorted_map/index_map.rs

@@ -1,7 +1,6 @@
 //! A variant of `SortedMap` that preserves insertion order.
 
 use std::hash::{Hash, Hasher};
-use std::iter::FromIterator;
 
 use crate::stable_hasher::{HashStable, StableHasher};
 use rustc_index::vec::{Idx, IndexVec};

compiler/rustc_data_structures/src/sso/either_iter.rs

@@ -1,7 +1,5 @@
 use std::fmt;
-use std::iter::ExactSizeIterator;
 use std::iter::FusedIterator;
-use std::iter::Iterator;
 
 /// Iterator which may contain instance of
 /// one of two specific implementations.

compiler/rustc_data_structures/src/sso/map.rs

@@ -3,7 +3,6 @@ use crate::fx::FxHashMap;
 use arrayvec::ArrayVec;
 use std::fmt;
 use std::hash::Hash;
-use std::iter::FromIterator;
 use std::ops::Index;
 
 // For pointer-sized arguments arrays

compiler/rustc_data_structures/src/sso/set.rs

@@ -1,6 +1,5 @@
 use std::fmt;
 use std::hash::Hash;
-use std::iter::FromIterator;
 
 use super::map::SsoHashMap;
 

compiler/rustc_data_structures/src/sync.rs

@@ -138,7 +138,7 @@ cfg_if! {
             }
         }
 
-        pub use std::iter::Iterator as ParallelIterator;
+        pub use Iterator as ParallelIterator;
 
         pub fn par_iter<T: IntoIterator>(t: T) -> T::IntoIter {
             t.into_iter()

compiler/rustc_data_structures/src/tagged_ptr/drop.rs

@@ -76,7 +76,7 @@ where
     fn drop(&mut self) {
         // No need to drop the tag, as it's Copy
         unsafe {
-            std::mem::drop(P::from_usize(self.raw.pointer_raw()));
+            drop(P::from_usize(self.raw.pointer_raw()));
         }
     }
 }

compiler/rustc_data_structures/src/vec_map.rs

@@ -1,6 +1,5 @@
 use std::borrow::Borrow;
 use std::fmt::Debug;
-use std::iter::FromIterator;
 use std::slice::Iter;
 use std::vec::IntoIter;
 

compiler/rustc_driver/src/lib.rs

@@ -45,7 +45,6 @@ use rustc_target::json::ToJson;
 
 use std::borrow::Cow;
 use std::cmp::max;
-use std::default::Default;
 use std::env;
 use std::ffi::OsString;
 use std::fs;

compiler/rustc_error_codes/src/error_codes/E0492.md

@@ -55,7 +55,6 @@ wrapper:
 
 ```
 use std::cell::Cell;
-use std::marker::Sync;
 
 struct NotThreadSafe<T> {
     value: Cell<T>,

compiler/rustc_errors/src/diagnostic_impls.rs

@@ -59,7 +59,7 @@ into_diagnostic_arg_using_display!(
     i128,
     u128,
     std::io::Error,
-    std::boxed::Box<dyn std::error::Error>,
+    Box<dyn std::error::Error>,
     std::num::NonZeroU32,
     hir::Target,
     Edition,

compiler/rustc_expand/src/base.rs

@@ -26,7 +26,6 @@ use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{BytePos, FileName, RealFileName, Span, DUMMY_SP};
 use smallvec::{smallvec, SmallVec};
 
-use std::default::Default;
 use std::iter;
 use std::path::PathBuf;
 use std::rc::Rc;

compiler/rustc_hir/src/pat_util.rs

@@ -6,7 +6,7 @@ use rustc_span::hygiene::DesugaringKind;
 use rustc_span::symbol::Ident;
 use rustc_span::Span;
 
-use std::iter::{Enumerate, ExactSizeIterator};
+use std::iter::Enumerate;
 
 pub struct EnumerateAndAdjust<I> {
     enumerate: Enumerate<I>,

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -31,7 +31,6 @@ use rustc_trait_selection::traits::{
 };
 
 use std::cell::LazyCell;
-use std::convert::TryInto;
 use std::iter;
 use std::ops::{ControlFlow, Deref};
 

compiler/rustc_incremental/src/persist/dirty_clean.rs

@@ -30,8 +30,6 @@ 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 std::vec::Vec;
 
 const LOADED_FROM_DISK: Symbol = sym::loaded_from_disk;
 const EXCEPT: Symbol = sym::except;

compiler/rustc_incremental/src/persist/fs.rs

@@ -113,7 +113,6 @@ use rustc_span::Symbol;
 
 use std::fs as std_fs;
 use std::io::{self, ErrorKind};
-use std::mem;
 use std::path::{Path, PathBuf};
 use std::time::{Duration, SystemTime, UNIX_EPOCH};
 
@@ -305,7 +304,7 @@ pub fn prepare_session_directory(
             }
 
             delete_session_dir_lock_file(sess, &lock_file_path);
-            mem::drop(directory_lock);
+            drop(directory_lock);
         }
     }
 }
@@ -864,7 +863,7 @@ pub fn garbage_collect_session_directories(sess: &Session) -> io::Result<()> {
 
                     // Let's make it explicit that the file lock is released at this point,
                     // or rather, that we held on to it until here
-                    mem::drop(lock);
+                    drop(lock);
                 }
                 Err(_) => {
                     debug!(
@@ -898,7 +897,7 @@ pub fn garbage_collect_session_directories(sess: &Session) -> io::Result<()> {
 
         // Let's make it explicit that the file lock is released at this point,
         // or rather, that we held on to it until here
-        mem::drop(lock);
+        drop(lock);
     }
 
     Ok(())

compiler/rustc_index/src/vec.rs

@@ -4,7 +4,6 @@ use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use std::fmt;
 use std::fmt::Debug;
 use std::hash::Hash;
-use std::iter::FromIterator;
 use std::marker::PhantomData;
 use std::ops::{Index, IndexMut, RangeBounds};
 use std::slice;

compiler/rustc_interface/src/tests.rs

@@ -25,7 +25,6 @@ use rustc_target::spec::{CodeModel, LinkerFlavorCli, MergeFunctions, PanicStrate
 use rustc_target::spec::{RelroLevel, SanitizerSet, SplitDebuginfo, StackProtector, TlsModel};
 
 use std::collections::{BTreeMap, BTreeSet};
-use std::iter::FromIterator;
 use std::num::NonZeroUsize;
 use std::path::{Path, PathBuf};
 

compiler/rustc_lexer/src/lib.rs

@@ -34,7 +34,6 @@ pub use crate::cursor::Cursor;
 use self::LiteralKind::*;
 use self::TokenKind::*;
 use crate::cursor::EOF_CHAR;
-use std::convert::TryFrom;
 
 /// Parsed token.
 /// It doesn't contain information about data that has been parsed,

compiler/rustc_lint/src/types.rs

@@ -16,7 +16,6 @@ use rustc_target::abi::{Abi, Size, WrappingRange};
 use rustc_target::abi::{Integer, TagEncoding, Variants};
 use rustc_target::spec::abi::Abi as SpecAbi;
 
-use std::cmp;
 use std::iter;
 use std::ops::ControlFlow;
 
@@ -531,7 +530,7 @@ impl<'tcx> LateLintPass<'tcx> for TypeLimits {
             _ => {}
         };
 
-        fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
+        fn is_valid<T: PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
             match binop.node {
                 hir::BinOpKind::Lt => v > min && v <= max,
                 hir::BinOpKind::Le => v >= min && v < max,