Make tidy errors red

This makes it easier to see them (and makes people go owo).

src/tools/tidy/Cargo.toml

@@ -11,6 +11,7 @@ miropt-test-tools = { path = "../miropt-test-tools" }
 lazy_static = "1"
 walkdir = "2"
 ignore = "0.4.18"
+termcolor = "1.1.3"
 
 [[bin]]
 name = "rust-tidy"

src/tools/tidy/src/lib.rs

@@ -3,6 +3,10 @@
 //! This library contains the tidy lints and exposes it
 //! to be used by tools.
 
+use std::fmt::Display;
+
+use termcolor::WriteColor;
+
 /// A helper macro to `unwrap` a result except also print out details like:
 ///
 /// * The expression that failed
@@ -26,18 +30,27 @@ macro_rules! t {
 }
 
 macro_rules! tidy_error {
-    ($bad:expr, $fmt:expr) => ({
-        *$bad = true;
-        eprint!("tidy error: ");
-        eprintln!($fmt);
-    });
-    ($bad:expr, $fmt:expr, $($arg:tt)*) => ({
-        *$bad = true;
-        eprint!("tidy error: ");
-        eprintln!($fmt, $($arg)*);
+    ($bad:expr, $($fmt:tt)*) => ({
+        $crate::tidy_error($bad, format_args!($($fmt)*)).expect("failed to output error");
     });
 }
 
+fn tidy_error(bad: &mut bool, args: impl Display) -> std::io::Result<()> {
+    use std::io::Write;
+    use termcolor::{Color, ColorChoice, ColorSpec, StandardStream};
+
+    *bad = true;
+
+    let mut stderr = StandardStream::stdout(ColorChoice::Auto);
+    stderr.set_color(ColorSpec::new().set_fg(Some(Color::Red)))?;
+
+    write!(&mut stderr, "tidy error")?;
+    stderr.set_color(&ColorSpec::new())?;
+
+    writeln!(&mut stderr, ": {args}")?;
+    Ok(())
+}
+
 pub mod alphabetical;
 pub mod bins;
 pub mod debug_artifacts;