Streamline configuration

Fixes triggermulti deserialization
Add 'generate-dhall' argument, which generates dhall for the config
enums.

src/config.rs

@@ -1,5 +1,7 @@
+use crate::StdError;
+use chrono::Utc;
 use serde::Deserialize;
-use serde_dhall::StaticType;
+use serde_dhall::{SimpleType, StaticType};
 use std::collections::HashMap;
 use std::error::Error;
 use std::fmt;
@@ -24,7 +26,11 @@ impl fmt::Display for Action {
     }
 }
 
-#[derive(Deserialize, StaticType, Debug)]
+// Newtype wrapper around a Vec of actions.
+// serde(transparent) and the imp StaticType below ensures we ignore the outer struct and
+// transparently deserialize into the inner vec.
+#[derive(Deserialize, Debug)]
+#[serde(transparent)]
 pub struct Actions(Vec<Action>);
 
 impl Actions {
@@ -40,6 +46,12 @@ impl fmt::Display for Actions {
     }
 }
 
+impl StaticType for Actions {
+    fn static_type() -> SimpleType {
+        SimpleType::List(Box::new(Action::static_type()))
+    }
+}
+
 #[derive(Deserialize, StaticType, Debug)]
 pub enum Mapping {
     NOP,                   // Do nothing.
@@ -87,16 +99,25 @@ pub struct Config {
 
 impl Config {
     pub fn from_file(p: &Path) -> Result<Self, Box<dyn Error>> {
-        match serde_dhall::from_file(p)
-            .with_builtin_type("Mapping".to_string(), Mapping::static_type())
-            .with_builtin_type("Action".to_string(), Action::static_type())
+        serde_dhall::from_file(p)
             .parse::<Self>()
-        {
-            Ok(c) => Ok(c),
-            Err(e) => {
-                println!("{}", e);
-                Err(Box::new(e))
-            }
-        }
+            .map_err(|e| e.into())
+    }
+
+    pub fn generate_prelude() -> StdError<()> {
+        let mut m = HashMap::new();
+        m.insert("Action".to_string(), Action::static_type());
+        m.insert("Mapping".to_string(), Mapping::static_type());
+        println!(
+            "-- Sampad Dhall types, autogenerated by git#{} on {}",
+            option_env!("VERSION").unwrap_or("unknown"),
+            Utc::now(),
+        );
+        println!(
+            "{{ Action = {}, Mapping = {} }}",
+            Action::static_type(),
+            Mapping::static_type()
+        );
+        Ok(())
     }
 }

src/main.rs

@@ -5,11 +5,14 @@ use config::{Action, Config, Mapping};
 use hidapi::HidApi;
 use rumqttc::{Client, MqttOptions, QoS};
 use std::collections::HashMap;
+use std::env;
 use std::error::Error;
 use std::path::Path;
 use std::thread;
 use tracing::{event, Level};
 
+type StdError<T> = Result<T, Box<dyn Error>>;
+
 struct State<'a> {
     mqtt_servers: HashMap<String, Client>,
     conf: &'a Config,
@@ -107,7 +110,19 @@ impl<'a> State<'a> {
     }
 }
 
-fn main() -> Result<(), Box<dyn Error>> {
+fn main() -> StdError<()> {
+    let args: Vec<_> = env::args().collect();
+    if let [prog, args @ ..] = &args[..] {
+        if args == ["generate-dhall"] {
+            return Config::generate_prelude();
+        } else if args.len() > 0 {
+            eprintln!("Usage: {} [generate-dhall]", prog);
+            return Err("Invalid usage".into());
+        }
+    } else {
+        unreachable!();
+    }
+
     tracing_subscriber::fmt::init();
     event!(Level::INFO, "Starting...");
     let conf = Config::from_file(Path::new("./config.dhall"))?;