Prompt user before installing things

xtask/src/deny.rs

@@ -45,11 +45,15 @@ pub fn deny(args: &[&str]) -> Result<(), DynError> {
 }
 
 fn install_cargo_deny() -> Result<(), DynError> {
-    let status = Command::new("cargo")
-        .args(["+stable", "install", "--quiet", "--locked", "cargo-deny"])
-        .status()?;
-    if !status.success() {
-        return Err(status.to_string().into());
+    let already_installed = Command::new("cargo")
+        .args(["deny", "--version"])
+        .output()
+        .is_ok_and(|out| out.status.success());
+    if already_installed {
+        return Ok(());
     }
-    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

@@ -3,6 +3,7 @@
 #![allow(clippy::exit)]
 
 mod deny;
+pub(crate) mod utils;
 
 type DynError = Box<dyn std::error::Error>;
 

xtask/src/utils.rs

@@ -0,0 +1,36 @@
+use std::{
+    env,
+    io::{self, Write as _},
+    process::Command,
+};
+
+use super::DynError;
+
+/// 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(())
+}