misc: Adapt consistent import style formatting

Historically the Cloud Hypervisor coding style has been to ensure that
all imports are ordered and placed in a single group. Unfortunately
cargo fmt has no support for ensuring that all imports are in a single
group so if whitespace lines were added as part of the import statements
then they would only be odered correctly in the group.

By adopting "group_imports="StdExternalCrate" we can enforce a style
where imports are placed in at most three groups for std, external
crates and the crate itself. Choosing a style enforceable by the tooling
reduces the reviewer burden.

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>

src/bin/ch-remote.rs

@@ -3,17 +3,18 @@
 // SPDX-License-Identifier: Apache-2.0
 //
 
+use std::fmt;
+use std::io::Read;
+use std::marker::PhantomData;
+use std::os::unix::net::UnixStream;
+use std::process;
+
 use api_client::simple_api_command;
 use api_client::simple_api_command_with_fds;
 use api_client::simple_api_full_command;
 use api_client::Error as ApiClientError;
 use clap::{Arg, ArgAction, ArgMatches, Command};
 use option_parser::{ByteSized, ByteSizedParseError};
-use std::fmt;
-use std::io::Read;
-use std::marker::PhantomData;
-use std::os::unix::net::UnixStream;
-use std::process;
 #[cfg(feature = "dbus_api")]
 use zbus::{proxy, zvariant::Optional};
 

src/main.rs

@@ -6,17 +6,18 @@
 #[macro_use]
 extern crate event_monitor;
 
+use std::fs::File;
+use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
+use std::sync::mpsc::channel;
+use std::sync::Mutex;
+use std::{env, io};
+
 use clap::{Arg, ArgAction, ArgGroup, ArgMatches, Command};
 use libc::EFD_NONBLOCK;
 use log::{warn, LevelFilter};
 use option_parser::OptionParser;
 use seccompiler::SeccompAction;
 use signal_hook::consts::SIGSYS;
-use std::fs::File;
-use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
-use std::sync::mpsc::channel;
-use std::sync::Mutex;
-use std::{env, io};
 use thiserror::Error;
 #[cfg(feature = "dbus_api")]
 use vmm::api::dbus::{dbus_api_graceful_shutdown, DBusApiOptions};
@@ -957,9 +958,8 @@ fn main() {
 
 #[cfg(test)]
 mod unit_tests {
-    use crate::config::HotplugMethod;
-    use crate::{create_app, prepare_default_values};
     use std::path::PathBuf;
+
     use vmm::config::{
         ConsoleConfig, ConsoleOutputMode, CpuFeatures, CpusConfig, MemoryConfig, PayloadConfig,
         RngConfig, VmConfig, VmParams,
@@ -967,6 +967,9 @@ mod unit_tests {
     #[cfg(target_arch = "x86_64")]
     use vmm::vm_config::DebugConsoleConfig;
 
+    use crate::config::HotplugMethod;
+    use crate::{create_app, prepare_default_values};
+
     fn get_vm_config_from_vec(args: &[&str]) -> VmConfig {
         let (default_vcpus, default_memory, default_rng) = prepare_default_values();
         let cmd_arguments =