rust-chg: install logger if $CHGDEBUG is set

This is modeled after the example logger and debugmsg() of chg/util.c.

https://docs.rs/log/0.4.5/log/#implementing-a-logger

rust/chg/src/main.rs

@@ -1,59 +1,98 b''
 // Copyright 2018 Yuya Nishihara <[e-mail]>
 //
 // This software may be used and distributed according to the terms of the
 // GNU General Public License version 2 or any later version.
 
 extern crate chg;
 extern crate futures;
+extern crate log;
 extern crate tokio;
 extern crate tokio_hglib;
 
 use chg::{ChgClientExt, ChgUiHandler};
 use chg::locator;
 use chg::procutil;
 use futures::sync::oneshot;
 use std::env;
 use std::io;
 use std::process;
+use std::time::Instant;
 use tokio::prelude::*;
 use tokio_hglib::UnixClient;
 
+struct DebugLogger {
+    start: Instant,
+}
+
+impl DebugLogger {
+    pub fn new() -> DebugLogger {
+        DebugLogger {
+            start: Instant::now(),
+        }
+    }
+}
+
+impl log::Log for DebugLogger {
+    fn enabled(&self, metadata: &log::Metadata) -> bool {
+        metadata.target().starts_with("chg::")
+    }
+
+    fn log(&self, record: &log::Record) {
+        if self.enabled(record.metadata()) {
+            // just make the output looks similar to chg of C
+            let l = format!("{}", record.level()).to_lowercase();
+            let t = self.start.elapsed();
+            writeln!(io::stderr(), "chg: {}: {}.{:06} {}",
+                     l, t.as_secs(), t.subsec_micros(), record.args()).unwrap_or(());
+        }
+    }
+
+    fn flush(&self) {
+    }
+}
+
 fn main() {
+    if env::var_os("CHGDEBUG").is_some() {
+        log::set_boxed_logger(Box::new(DebugLogger::new()))
+            .expect("any logger should not be installed yet");
+        log::set_max_level(log::LevelFilter::Debug);
+    }
+
     let code = run().unwrap_or_else(|err| {
         writeln!(io::stderr(), "chg: abort: {}", err).unwrap_or(());
         255
     });
     process::exit(code);
 }
 
 fn run() -> io::Result<i32> {
     let current_dir = env::current_dir()?;
     let sock_path = locator::prepare_server_socket_path()?;
     let handler = ChgUiHandler::new();
     let (result_tx, result_rx) = oneshot::channel();
     let fut = UnixClient::connect(sock_path)
         .and_then(|client| {
             client.set_current_dir(current_dir)
         })
         .and_then(|client| {
             client.attach_io(io::stdin(), io::stdout(), io::stderr())
         })
         .and_then(|client| {
             let pid = client.server_spec().process_id.unwrap();
             let pgid = client.server_spec().process_group_id;
             procutil::setup_signal_handler_once(pid, pgid)?;
             Ok(client)
         })
         .and_then(|client| {
             client.run_command_chg(handler, env::args_os().skip(1))
         })
         .map(|(_client, _handler, code)| {
             procutil::restore_signal_handler_once()?;
             Ok(code)
         })
         .or_else(|err| Ok(Err(err)))  // pass back error to caller
         .map(|res| result_tx.send(res).unwrap());
     tokio::run(fut);
     result_rx.wait().unwrap_or(Err(io::Error::new(io::ErrorKind::Other,
                                                   "no exit code set")))
 }