Add xtask crate (#4293)

Replaces only the cargo_deny.sh script for now. Can be expanded over
time to replace the other shell and python scripts, so only Rust is
needed to work with the repository.

Closes <https://github.com/emilk/egui/issues/2887>
Closes <https://github.com/emilk/egui/issues/4373>

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

xtask/src/deny.rs

@@ -0,0 +1,60 @@
+//! Run `cargo deny`
+//!
+//! Also installs the subcommand if it is not already installed.
+
+use std::process::Command;
+
+use super::DynError;
+
+pub fn deny(args: &[&str]) -> Result<(), DynError> {
+    if !args.is_empty() {
+        return Err(format!("Invalid arguments: {args:?}").into());
+    }
+    install_cargo_deny()?;
+    let targets = [
+        "aarch64-apple-darwin",
+        "aarch64-linux-android",
+        "i686-pc-windows-gnu",
+        "i686-pc-windows-msvc",
+        "i686-unknown-linux-gnu",
+        "wasm32-unknown-unknown",
+        "x86_64-apple-darwin",
+        "x86_64-pc-windows-gnu",
+        "x86_64-pc-windows-msvc",
+        "x86_64-unknown-linux-gnu",
+        "x86_64-unknown-linux-musl",
+        "x86_64-unknown-redox",
+    ];
+    for target in targets {
+        let mut cmd = Command::new("cargo");
+        cmd.args([
+            "deny",
+            "--all-features",
+            "--log-level",
+            "error",
+            "--target",
+            target,
+            "check",
+        ]);
+        super::utils::print_cmd(&cmd);
+        let status = cmd.status()?;
+        if !status.success() {
+            return Err(status.to_string().into());
+        }
+    }
+    Ok(())
+}
+
+fn install_cargo_deny() -> Result<(), DynError> {
+    let already_installed = Command::new("cargo")
+        .args(["deny", "--version"])
+        .output()
+        .is_ok_and(|out| out.status.success());
+    if already_installed {
+        return Ok(());
+    }
+    let mut cmd = Command::new("cargo");
+    cmd.args(["+stable", "install", "--quiet", "--locked", "cargo-deny"]);
+    let reason = "install cargo-deny";
+    super::utils::ask_to_run(cmd, true, reason)
+}

xtask/src/main.rs

@@ -0,0 +1,40 @@
+#![allow(clippy::print_stdout)]
+#![allow(clippy::print_stderr)]
+#![allow(clippy::exit)]
+
+mod deny;
+pub(crate) mod utils;
+
+type DynError = Box<dyn std::error::Error>;
+
+fn main() {
+    if let Err(e) = try_main() {
+        eprintln!("{e}");
+        std::process::exit(-1);
+    }
+}
+
+fn try_main() -> Result<(), DynError> {
+    let arg_strings: Vec<_> = std::env::args().skip(1).collect();
+    let args: Vec<_> = arg_strings.iter().map(String::as_str).collect();
+
+    match args.as_slice() {
+        &[] | &["-h"] | &["--help"] => print_help(),
+        &["deny", ..] => deny::deny(&args[1..])?,
+        c => Err(format!("Invalid arguments {c:?}"))?,
+    }
+    Ok(())
+}
+
+fn print_help() {
+    let help = "
+    xtask help
+
+    Subcommands
+    deny: Run cargo-deny for all targets
+
+    Options
+    -h, --help: print help and exit
+        ";
+    println!("{help}");
+}

xtask/src/utils.rs

@@ -0,0 +1,45 @@
+use std::{
+    env,
+    io::{self, Write as _},
+    process::Command,
+};
+
+use super::DynError;
+
+/// Print the command and its arguments as if the user had typed them
+pub fn print_cmd(cmd: &Command) {
+    print!("{} ", cmd.get_program().to_string_lossy());
+    for arg in cmd.get_args() {
+        print!("{} ", arg.to_string_lossy());
+    }
+    println!();
+}
+
+/// Prompt user before running a command
+///
+/// Adapted from [miri](https://github.com/rust-lang/miri/blob/dba35d2be72f4b78343d1a0f0b4737306f310672/cargo-miri/src/util.rs#L181-L204)
+pub fn ask_to_run(mut cmd: Command, ask: bool, reason: &str) -> Result<(), DynError> {
+    // Disable interactive prompts in CI (GitHub Actions, Travis, AppVeyor, etc).
+    // Azure doesn't set `CI` though (nothing to see here, just Microsoft being Microsoft),
+    // so we also check their `TF_BUILD`.
+    let is_ci = env::var_os("CI").is_some() || env::var_os("TF_BUILD").is_some();
+    if ask && !is_ci {
+        let mut buf = String::new();
+        print!("The script is going to run: \n\n`{cmd:?}`\n\n To {reason}.\nProceed? [Y/n] ",);
+        io::stdout().flush().unwrap();
+        io::stdin().read_line(&mut buf).unwrap();
+        match buf.trim().to_lowercase().as_ref() {
+            "" | "y" | "yes" => {}
+            "n" | "no" => return Err("Aborting as per your request".into()),
+            a => return Err(format!("Invalid answer `{a}`").into()),
+        };
+    } else {
+        eprintln!("Running `{cmd:?}` to {reason}.");
+    }
+
+    let status = cmd.status()?;
+    if !status.success() {
+        return Err(format!("failed to {reason}: {status}").into());
+    }
+    Ok(())
+}