Add rustfilt-like implementation

src/main.rs

@@ -0,0 +1,34 @@
+//! Minimal implementation of rustc-demangle as a binary.
+//!
+//! This is not intended to be a feature-rich binary, e.g., argument parsing is unlikely to be
+//! added. However it's usable for most use cases and as of writing is ~2x faster than rustfilt.
+
+use std::io;
+use std::process::ExitCode;
+
+#[cfg(not(feature = "std"))]
+compile_error!("Currently the std feature is required for building the binary");
+
+fn main() -> ExitCode {
+    if std::env::args_os().count() > 1 {
+        eprintln!("No arguments expected. Pass input on stdin.");
+        return ExitCode::FAILURE;
+    }
+
+    let mut input = io::stdin().lock();
+    let mut output = io::stdout().lock();
+
+    let Err(e) = rustc_demangle::demangle_stream(&mut input, &mut output, false) else {
+        return ExitCode::SUCCESS;
+    };
+
+    // Don't print any extra output if we hit BrokenPipe, just exit.
+    if e.kind() == std::io::ErrorKind::BrokenPipe {
+        // FIXME: This isn't quite the same as a SIGPIPE failure, but it's probably close enough for
+        // our purposes.
+        return ExitCode::FAILURE;
+    }
+
+    eprintln!("Failed: {}", e);
+    ExitCode::FAILURE
+}