x: introduce 'cargo xfmt', a wrapper around 'cargo fmt'

Introduce 'xfmt', a wrapper around 'cargo fmt' which works around the
issue that the 'merge_imports' config of rustfmt isn't stable.

If you place an unstable config in a rustfmt.toml config file and run
using a stable version of rustfmt the config is ignored and you get the
following:

    $ cargo fmt
    Warning: can't set `merge_imports = true`, unstable features are only available in nightly channel.

But if you instead pass the config using the '--config' option rustfmt
happily applies and uses the unstable config:

    $ cargo fmt -- --config merge_imports=true

Since there are enough people on the project that would like to see
imports merged the new 'xfmt' wrapper uses the abbove workaround to
ensure that imports are merged when running 'cargo xfmt'.

If you also want to have the following behavior with your favorite
editor (assuming your editor lets you pass additional flags to rustfmt)
you can simply add '--config merge_imports=true' to the list of options
your editor passes rustfmt when formatting rust code. For example with
vim and the rust.vim plugin you would just need to add the following to
your vimrc to have imports merged when rust.vim is used to format your
code:

    let g:rustfmt_options = '--config merge_imports=true'

Closes: aptos-labs#2926
Approved by: bothra90

.cargo/config

@@ -2,4 +2,5 @@
 x = "run --package x --bin x --"
 xcheck = "run --package x --bin x -- check"
 xclippy = "run --package x --bin x -- clippy"
+xfmt = "run --package x --bin x -- fmt"
 xtest = "run --package x --bin x -- test"

x/src/cargo.rs

@@ -24,6 +24,11 @@ impl Cargo {
         }
     }
 
+    pub fn all(&mut self) -> &mut Self {
+        self.inner.arg("--all");
+        self
+    }
+
     pub fn workspace(&mut self) -> &mut Self {
         self.inner.arg("--workspace");
         self

x/src/fmt.rs

@@ -0,0 +1,44 @@
+// Copyright (c) The Libra Core Contributors
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::{cargo::Cargo, config::Config, Result};
+use std::ffi::OsString;
+use structopt::StructOpt;
+
+#[derive(Debug, StructOpt)]
+pub struct Args {
+    #[structopt(long)]
+    /// Run in 'check' mode. Exits with 0 if input is
+    /// formatted correctly. Exits with 1 and prints a diff if
+    /// formatting is required.
+    check: bool,
+
+    #[structopt(long)]
+    /// Run check on all packages in the workspace
+    workspace: bool,
+
+    #[structopt(name = "ARGS", parse(from_os_str), last = true)]
+    /// Pass through args to rustfmt
+    args: Vec<OsString>,
+}
+
+pub fn run(args: Args, _config: Config) -> Result<()> {
+    // Hardcode that we want imports merged
+    let mut pass_through_args = vec!["--config".into(), "merge_imports=true".into()];
+
+    if args.check {
+        pass_through_args.push("--check".into());
+    }
+
+    pass_through_args.extend(args.args);
+
+    let mut cmd = Cargo::new("fmt");
+
+    if args.workspace {
+        // cargo fmt doesn't have a --workspace flag, instead it uses the
+        // old --all flag
+        cmd.all();
+    }
+
+    cmd.pass_through(&pass_through_args).run()
+}

x/src/main.rs

@@ -10,6 +10,7 @@ mod cargo;
 mod check;
 mod clippy;
 mod config;
+mod fmt;
 mod lint;
 mod test;
 mod utils;
@@ -33,6 +34,9 @@ enum Command {
     #[structopt(name = "clippy")]
     /// Run `cargo clippy`
     Clippy(clippy::Args),
+    #[structopt(name = "fmt")]
+    /// Run `cargo fmt`
+    Fmt(fmt::Args),
     #[structopt(name = "test")]
     /// Run tests
     Test(test::Args),
@@ -49,6 +53,7 @@ fn main() -> Result<()> {
         Command::Test(args) => test::run(args, config),
         Command::Check(args) => check::run(args, config),
         Command::Clippy(args) => clippy::run(args, config),
+        Command::Fmt(args) => fmt::run(args, config),
         Command::Bench(args) => bench::run(args, config),
         Command::Lint(args) => lint::run(args, config),
     }