1 files changed, 94 insertions, 0 deletions
diff --git a/third_party/rust/clap/examples/repl.rs b/third_party/rust/clap/examples/repl.rs
new file mode 100644
index 0000000000..f1b65c3090
--- /dev/null
+++ b/third_party/rust/clap/examples/repl.rs
@@ -0,0 +1,94 @@
+// Note: this requires the `unstable-multicall` feature
+
+use std::io::Write;
+
+use clap::Command;
+
+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 matches = cli()
+        .try_get_matches_from(&args)
+        .map_err(|e| e.to_string())?;
+    match matches.subcommand() {
+        Some(("ping", _matches)) => {
+            write!(std::io::stdout(), "Pong").map_err(|e| e.to_string())?;
+            std::io::stdout().flush().map_err(|e| e.to_string())?;
+        }
+        Some(("quit", _matches)) => {
+            write!(std::io::stdout(), "Exiting ...").map_err(|e| e.to_string())?;
+            std::io::stdout().flush().map_err(|e| e.to_string())?;
+            return Ok(true);
+        }
+        Some((name, _matches)) => unimplemented!("{}", name),
+        None => unreachable!("subcommand required"),
+    }
+
+    Ok(false)
+}
+
+fn cli() -> Command<'static> {
+    // strip out usage
+    const PARSER_TEMPLATE: &str = "\
+        {all-args}
+    ";
+    // strip out name/version
+    const APPLET_TEMPLATE: &str = "\
+        {about-with-newline}\n\
+        {usage-heading}\n    {usage}\n\
+        \n\
+        {all-args}{after-help}\
+    ";
+
+    Command::new("repl")
+        .multicall(true)
+        .arg_required_else_help(true)
+        .subcommand_required(true)
+        .subcommand_value_name("APPLET")
+        .subcommand_help_heading("APPLETS")
+        .help_template(PARSER_TEMPLATE)
+        .subcommand(
+            Command::new("ping")
+                .about("Get a response")
+                .help_template(APPLET_TEMPLATE),
+        )
+        .subcommand(
+            Command::new("quit")
+                .alias("exit")
+                .about("Quit the REPL")
+                .help_template(APPLET_TEMPLATE),
+        )
+}
+
+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)
+}