avoid spurious 'Preparing a sysroot for Miri...' in 'cargo miri setup --print-sysroot'

also clean up sysroot building printing logic a bit

Author: RalfJung

cargo-miri/bin.rs

@@ -35,6 +35,11 @@ The cargo options are exactly the same as for `cargo run` and `cargo test`, resp
 Examples:
     cargo miri run
     cargo miri test -- test-suite-filter
+
+    cargo miri setup --print sysroot
+        This will print the path to the generated sysroot (and nothing else) on stdout.
+        stderr will still contain progress information about how the build is doing.
+
 "#;
 
 #[derive(Clone, Debug)]
@@ -361,17 +366,15 @@ fn write_to_file(filename: &Path, content: &str) {
 /// done all this already.
 fn setup(subcommand: &MiriCommand) {
     let only_setup = matches!(subcommand, MiriCommand::Setup);
+    let ask_user = !only_setup;
+    let print_sysroot = only_setup && has_arg_flag("--print-sysroot"); // whether we just print the sysroot path
     if std::env::var_os("MIRI_SYSROOT").is_some() {
         if only_setup {
             println!("WARNING: MIRI_SYSROOT already set, not doing anything.")
         }
         return;
     }
 
-    // Subcommands other than `setup` will do a setup if necessary, but
-    // interactively confirm first.
-    let ask_user = !only_setup;
-
     // First, we need xargo.
     if xargo_version().map_or(true, |v| v < XARGO_MIN_VERSION) {
         if std::env::var_os("XARGO_CHECK").is_some() {
@@ -507,8 +510,14 @@ path = "lib.rs"
     command.env("RUSTFLAGS", "-Cdebug-assertions=off -Coverflow-checks=on");
     // Manage the output the user sees.
     if only_setup {
+        // We want to be explicit.
         eprintln!("Preparing a sysroot for Miri...");
+        if print_sysroot {
+            // Be extra sure there is no noise on stdout.
+            command.stdout(process::Stdio::null());
+        }
     } else {
+        // We want to be quiet, but still let the user know that something is happening.
         eprint!("Preparing a sysroot for Miri... ");
         command.stdout(process::Stdio::null());
         command.stderr(process::Stdio::null());
@@ -523,22 +532,21 @@ path = "lib.rs"
             ))
         }
     }
-    if !only_setup {
-        eprintln!("done");
-    }
 
     // That should be it! But we need to figure out where xargo built stuff.
     // Unfortunately, it puts things into a different directory when the
     // architecture matches the host.
     let sysroot = if target == &host { dir.join("HOST") } else { PathBuf::from(dir) };
     std::env::set_var("MIRI_SYSROOT", &sysroot); // pass the env var to the processes we spawn, which will turn it into "--sysroot" flags
     // Figure out what to print.
-    let print_sysroot = only_setup && has_arg_flag("--print-sysroot"); // whether we just print the sysroot path
+    if only_setup {
+        eprintln!("A sysroot for Miri is now available in `{}`.", sysroot.display());
+    } else {
+        eprintln!("done");
+    }
     if print_sysroot {
         // Print just the sysroot and nothing else to stdout; this way we do not need any escaping.
         println!("{}", sysroot.display());
-    } else if only_setup {
-        eprintln!("A sysroot for Miri is now available in `{}`.", sysroot.display());
     }
 }
 

miri

@@ -131,9 +131,6 @@ export RUSTFLAGS="-C link-args=-Wl,-rpath,$LIBDIR $RUSTFLAGS"
 
 # Build a sysroot and set MIRI_SYSROOT to use it. Arguments are passed to `cargo miri setup`.
 build_sysroot() {
-    # Build once, for the user to see.
-    $CARGO run $CARGO_EXTRA_FLAGS --manifest-path "$MIRIDIR"/cargo-miri/Cargo.toml -- miri setup "$@"
-    # Call again, to just set env var.
     export MIRI_SYSROOT="$($CARGO run $CARGO_EXTRA_FLAGS --manifest-path "$MIRIDIR"/cargo-miri/Cargo.toml -q -- miri setup --print-sysroot "$@")"
 }