Add --loglevel and --develop

--loglevel sets the log level for all of nu
--develop takes a list of modules and turns on trace mode for them

src/main.rs

@@ -17,10 +17,58 @@ mod prelude;
 mod shell;
 mod stream;
 
+use clap::{App, Arg};
+use log::LevelFilter;
 use std::error::Error;
 
 fn main() -> Result<(), Box<Error>> {
-    pretty_env_logger::init();
+    let matches = App::new("nu shell")
+        .version("0.5")
+        .arg(
+            Arg::with_name("loglevel")
+                .short("l")
+                .long("loglevel")
+                .value_name("LEVEL")
+                .possible_values(&["error", "warn", "info", "debug", "trace"])
+                .takes_value(true),
+        )
+        .arg(
+            Arg::with_name("develop")
+                .long("develop")
+                .multiple(true)
+                .takes_value(true),
+        )
+        .get_matches();
+
+    let loglevel = match matches.value_of("loglevel") {
+        None => LevelFilter::Warn,
+        Some("error") => LevelFilter::Error,
+        Some("warn") => LevelFilter::Warn,
+        Some("info") => LevelFilter::Info,
+        Some("debug") => LevelFilter::Debug,
+        Some("trace") => LevelFilter::Trace,
+        _ => unreachable!(),
+    };
+
+    let mut builder = pretty_env_logger::formatted_builder();
+
+    if let Ok(s) = std::env::var("RUST_LOG") {
+        builder.parse_filters(&s);
+    }
+
+    builder.filter_module("nu", loglevel);
+
+    match matches.values_of("develop") {
+        None => {}
+        Some(values) => for item in values {
+            println!("filtering {:?}", item);
+            builder.filter_module(&format!("nu::{}", item), LevelFilter::Trace);
+        } //println!("{:?}", values.collect::<Vec<&str>>()),
+    }
+
+    builder.try_init()?;
+
+    // pretty_env_logger::init();
     futures::executor::block_on(crate::cli::cli())?;
     Ok(())
 }