Fix 2018 idiom lints

This lint is allow by default, which is why this wasn't spotted earlier.
It's denied by rust-lang/rust, so it's good to warn about it here so it
can be fixed more quickly.

Author: jyn514

crates/assert-instr-macro/src/lib.rs

@@ -7,6 +7,7 @@
 //! The procedural macro here is relatively simple, it simply appends a
 //! `#[test]` function to the original token stream which asserts that the
 //! function itself contains the relevant instruction.
+#![deny(rust_2018_idioms)]
 
 extern crate proc_macro;
 extern crate proc_macro2;
@@ -177,7 +178,7 @@ struct Invoc {
 }
 
 impl syn::parse::Parse for Invoc {
-    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+    fn parse(input: syn::parse::ParseStream<'_>) -> syn::Result<Self> {
         use syn::{ext::IdentExt, Token};
 
         let mut instr = String::new();

crates/core_arch/src/lib.rs

@@ -2,6 +2,7 @@
 #![allow(improper_ctypes_definitions)]
 #![allow(dead_code)]
 #![allow(unused_features)]
+#![deny(rust_2018_idioms)]
 #![feature(
     asm,
     const_fn,

crates/simd-test-macro/src/lib.rs

@@ -2,6 +2,7 @@
 //!
 //! This macro expands to a `#[test]` function which tests the local machine
 //! for the appropriate cfg before calling the inner test function.
+#![deny(rust_2018_idioms)]
 
 extern crate proc_macro;
 extern crate proc_macro2;

crates/std_detect/src/detect/os/linux/cpuinfo.rs

@@ -17,7 +17,7 @@ impl CpuInfo {
         })
     }
     /// Returns the value of the cpuinfo `field`.
-    pub(crate) fn field(&self, field: &str) -> CpuInfoField {
+    pub(crate) fn field(&self, field: &str) -> CpuInfoField<'_> {
         for l in self.raw.lines() {
             if l.trim().starts_with(field) {
                 return CpuInfoField::new(l.split(": ").nth(1));

crates/std_detect/src/lib.rs

@@ -13,14 +13,16 @@
 
 #![unstable(feature = "stdsimd", issue = "27731")]
 #![feature(const_fn, staged_api, stdsimd, doc_cfg, allow_internal_unstable)]
+#![deny(rust_2018_idioms)]
 #![allow(clippy::shadow_reuse)]
 #![deny(clippy::missing_inline_in_public_items)]
 #![cfg_attr(all(target_os = "freebsd", target_arch = "aarch64"), feature(asm))]
 #![cfg_attr(test, allow(unused_imports))]
 #![cfg_attr(feature = "std_detect_file_io", feature(vec_spare_capacity))]
 #![no_std]
 
-#[cfg_attr(feature = "rustc-dep-of-std", allow(unused_extern_crates))]
+// rust-lang/rust#83888: removing `extern crate` gives an error that `vec_spare_capacity` is unknown
+#[cfg_attr(feature = "std_detect_file_io", allow(unused_extern_crates))]
 #[cfg(feature = "std_detect_file_io")]
 extern crate alloc;
 

crates/stdarch-test/src/lib.rs

@@ -4,13 +4,12 @@
 //! output once globally and then provides the `assert` function which makes
 //! assertions about the disassembly of a function.
 #![feature(test)] // For black_box
+#![deny(rust_2018_idioms)]
 #![allow(clippy::missing_docs_in_private_items, clippy::print_stdout)]
 
 extern crate assert_instr_macro;
-extern crate cc;
 #[macro_use]
 extern crate lazy_static;
-extern crate rustc_demangle;
 extern crate simd_test_macro;
 #[macro_use]
 extern crate cfg_if;

crates/stdarch-verify/src/lib.rs

@@ -1,5 +1,4 @@
-extern crate proc_macro;
-extern crate proc_macro2;
+#![deny(rust_2018_idioms)]
 #[macro_use]
 extern crate quote;
 #[macro_use]
@@ -357,7 +356,7 @@ fn find_instrs(attrs: &[syn::Attribute]) -> Vec<String> {
     // TODO: should probably just reuse `Invoc` from the `assert-instr-macro`
     // crate.
     impl syn::parse::Parse for AssertInstr {
-        fn parse(content: syn::parse::ParseStream) -> syn::Result<Self> {
+        fn parse(content: syn::parse::ParseStream<'_>) -> syn::Result<Self> {
             let input;
             parenthesized!(input in content);
             let _ = input.parse::<syn::Meta>()?;
@@ -443,7 +442,7 @@ struct RustcArgsRequiredConst {
 }
 
 impl syn::parse::Parse for RustcArgsRequiredConst {
-    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+    fn parse(input: syn::parse::ParseStream<'_>) -> syn::Result<Self> {
         let content;
         parenthesized!(content in input);
         let list =