compiler: remove unnecessary imports and qualified paths

compiler/rustc_query_system/src/dep_graph/graph.rs

@@ -46,7 +46,7 @@ impl DepNodeIndex {
     pub const FOREVER_RED_NODE: DepNodeIndex = DepNodeIndex::from_u32(1);
 }
 
-impl std::convert::From<DepNodeIndex> for QueryInvocationId {
+impl From<DepNodeIndex> for QueryInvocationId {
     #[inline]
     fn from(dep_node_index: DepNodeIndex) -> Self {
         QueryInvocationId(dep_node_index.as_u32())

compiler/rustc_query_system/src/dep_graph/serialized.rs

@@ -22,7 +22,6 @@ use rustc_index::vec::{Idx, IndexVec};
 use rustc_serialize::opaque::{FileEncodeResult, FileEncoder, IntEncodedWithFixedSize, MemDecoder};
 use rustc_serialize::{Decodable, Decoder, Encodable};
 use smallvec::SmallVec;
-use std::convert::TryInto;
 
 // The maximum value of `SerializedDepNodeIndex` leaves the upper two bits
 // unused so that we can store multiple index types in `CompressedHybridIndex`,

compiler/rustc_query_system/src/query/caches.rs

@@ -9,7 +9,6 @@ use rustc_data_structures::sharded::Sharded;
 use rustc_data_structures::sync::Lock;
 use rustc_data_structures::sync::WorkerLocal;
 use rustc_index::vec::{Idx, IndexVec};
-use std::default::Default;
 use std::fmt::Debug;
 use std::hash::Hash;
 use std::marker::PhantomData;

compiler/rustc_query_system/src/query/job.rs

@@ -22,8 +22,8 @@ use {
     rustc_data_structures::{jobserver, OnDrop},
     rustc_rayon_core as rayon_core,
     rustc_span::DUMMY_SP,
-    std::iter::{self, FromIterator},
-    std::{mem, process},
+    std::iter,
+    std::process,
 };
 
 /// Represents a span and a query key.
@@ -247,7 +247,7 @@ impl QueryLatch {
             jobserver::release_thread();
             waiter.condvar.wait(&mut info);
             // Release the lock before we potentially block in `acquire_thread`
-            mem::drop(info);
+            drop(info);
             jobserver::acquire_thread();
         }
     }