Rollup merge of rust-lang#58318 - taiki-e:libserialize-2018, r=Centril

libserialize => 2018

Transitions `libserialize` to Rust 2018; cc rust-lang#58099

This includes a commit from rust-lang#58252 (thanks @h-michael!)

r? @Centril

src/libserialize/Cargo.toml

@@ -2,6 +2,7 @@
 authors = ["The Rust Project Developers"]
 name = "serialize"
 version = "0.0.0"
+edition = "2018"
 
 [lib]
 name = "serialize"

src/libserialize/collection_impls.rs

@@ -2,7 +2,7 @@
 
 use std::hash::{Hash, BuildHasher};
 
-use {Decodable, Encodable, Decoder, Encoder};
+use crate::{Decodable, Encodable, Decoder, Encoder};
 use std::collections::{LinkedList, VecDeque, BTreeMap, BTreeSet, HashMap, HashSet};
 use std::rc::Rc;
 use std::sync::Arc;

src/libserialize/hex.rs

@@ -60,7 +60,7 @@ pub enum FromHexError {
 }
 
 impl fmt::Display for FromHexError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
             InvalidHexCharacter(ch, idx) =>
                 write!(f, "Invalid character '{}' at position {}", ch, idx),
@@ -145,8 +145,8 @@ impl FromHex for str {
 #[cfg(test)]
 mod tests {
     extern crate test;
-    use self::test::Bencher;
-    use hex::{FromHex, ToHex};
+    use test::Bencher;
+    use crate::hex::{FromHex, ToHex};
 
     #[test]
     pub fn test_to_hex() {