chore: checkpoint before Python removal

vendor/clap/examples/repl-derive.rs

@@ -0,0 +1,67 @@
+use std::io::Write;
+
+use clap::{Parser, Subcommand};
+
+fn main() -> Result<(), String> {
+    loop {
+        let line = readline()?;
+        let line = line.trim();
+        if line.is_empty() {
+            continue;
+        }
+
+        match respond(line) {
+            Ok(quit) => {
+                if quit {
+                    break;
+                }
+            }
+            Err(err) => {
+                write!(std::io::stdout(), "{err}").map_err(|e| e.to_string())?;
+                std::io::stdout().flush().map_err(|e| e.to_string())?;
+            }
+        }
+    }
+
+    Ok(())
+}
+
+fn respond(line: &str) -> Result<bool, String> {
+    let args = shlex::split(line).ok_or("error: Invalid quoting")?;
+    let cli = Cli::try_parse_from(args).map_err(|e| e.to_string())?;
+    match cli.command {
+        Commands::Ping => {
+            write!(std::io::stdout(), "Pong").map_err(|e| e.to_string())?;
+            std::io::stdout().flush().map_err(|e| e.to_string())?;
+        }
+        Commands::Exit => {
+            write!(std::io::stdout(), "Exiting ...").map_err(|e| e.to_string())?;
+            std::io::stdout().flush().map_err(|e| e.to_string())?;
+            return Ok(true);
+        }
+    }
+    Ok(false)
+}
+
+#[derive(Debug, Parser)]
+#[command(multicall = true)]
+struct Cli {
+    #[command(subcommand)]
+    command: Commands,
+}
+
+#[derive(Debug, Subcommand)]
+enum Commands {
+    Ping,
+    Exit,
+}
+
+fn readline() -> Result<String, String> {
+    write!(std::io::stdout(), "$ ").map_err(|e| e.to_string())?;
+    std::io::stdout().flush().map_err(|e| e.to_string())?;
+    let mut buffer = String::new();
+    std::io::stdin()
+        .read_line(&mut buffer)
+        .map_err(|e| e.to_string())?;
+    Ok(buffer)
+}