fixup! Reimplement example, compile only with "json" feature enabled

Author: matthiasbeyer

examples/async_source/main.rs

@@ -5,7 +5,6 @@ mod example {
     use config::{builder::AsyncState, AsyncSource, ConfigBuilder, ConfigError, FileFormat, Map};
 
     use async_trait::async_trait;
-    use futures::{select, FutureExt};
     use warp::Filter;
 
     // Example below presents sample configuration server and client.
@@ -14,7 +13,7 @@ mod example {
     // Client consumes it using custom HTTP AsyncSource built on top of reqwest.
 
 
-    async fn run_server() -> Result<(), Box<dyn Error>> {
+    pub async fn run_server() -> Result<(), Box<dyn Error>> {
         let service = warp::path("configuration").map(|| r#"{ "value" : 123 }"#);
 
         println!("Running server on localhost:5001");
@@ -24,7 +23,7 @@ mod example {
         Ok(())
     }
 
-    async fn run_client() -> Result<(), Box<dyn Error>> {
+    pub async fn run_client() -> Result<(), Box<dyn Error>> {
         // Good enough for an example to allow server to start
         tokio::time::sleep(tokio::time::Duration::from_secs(3)).await;
 
@@ -70,7 +69,8 @@ mod example {
 
 #[cfg(feature = "json")]
 #[tokio::main]
-async fn main() -> Result<(), Box<dyn Error>> {
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    use futures::{select, FutureExt};
     select! {
         r = example::run_server().fuse() => r,
         r = example::run_client().fuse() => r