Gate async-traits behind a feature

Author: nstinus

Cargo.toml

@@ -15,20 +15,21 @@ edition = "2018"
 maintenance = { status = "actively-developed" }
 
 [features]
-default = ["toml", "json", "yaml", "ini", "ron", "json5", "convert-case"]
+default = ["toml", "json", "yaml", "ini", "ron", "json5", "convert-case", "async"]
 json = ["serde_json"]
 yaml = ["yaml-rust"]
 ini = ["rust-ini"]
 json5 = ["json5_rs"]
 convert-case = ["convert_case"]
 preserve_order = ["indexmap", "toml/preserve_order", "serde_json/preserve_order", "ron/indexmap"]
+async = ["async-trait"]
 
 [dependencies]
-async-trait = "0.1.50"
 lazy_static = "1.0"
 serde = "1.0.8"
 nom = "7"
 
+async-trait = { version = "0.1.50", optional = true }
 toml = { version = "0.5", optional = true }
 serde_json = { version = "1.0.2", optional = true }
 yaml-rust = { version = "0.4", optional = true }

src/builder.rs

@@ -1,8 +1,8 @@
-use std::iter::IntoIterator;
 use std::str::FromStr;
 
 use crate::error::Result;
 use crate::map::Map;
+#[cfg(feature = "async")]
 use crate::source::AsyncSource;
 use crate::{config::Config, path::Expression, source::Source, value::Value};
 
@@ -132,6 +132,7 @@ pub struct AsyncState {
 #[derive(Debug, Clone)]
 enum SourceType {
     Sync(Box<dyn Source + Send + Sync>),
+    #[cfg(feature = "async")]
     Async(Box<dyn AsyncSource + Send + Sync>),
 }
 
@@ -213,6 +214,7 @@ impl ConfigBuilder<DefaultState> {
     /// Registers new [`AsyncSource`] in this builder and forces transition to [`AsyncState`].
     ///
     /// Calling this method does not invoke any I/O. [`AsyncSource`] is only saved in internal register for later use.
+    #[cfg(feature = "async")]
     pub fn add_async_source<T>(self, source: T) -> ConfigBuilder<AsyncState>
     where
         T: AsyncSource + Send + Sync + 'static,
@@ -302,6 +304,7 @@ impl ConfigBuilder<AsyncState> {
     /// Registers new [`AsyncSource`] in this builder.
     ///
     /// Calling this method does not invoke any I/O. [`AsyncSource`] is only saved in internal register for later use.
+    #[cfg(feature = "async")]
     pub fn add_async_source<T>(mut self, source: T) -> Self
     where
         T: AsyncSource + Send + Sync + 'static,
@@ -354,6 +357,7 @@ impl ConfigBuilder<AsyncState> {
         for source in sources.iter() {
             match source {
                 SourceType::Sync(source) => source.collect_to(&mut cache)?,
+                #[cfg(feature = "async")]
                 SourceType::Async(source) => source.collect_to(&mut cache).await?,
             }
         }

src/lib.rs

@@ -40,7 +40,9 @@ pub use crate::error::ConfigError;
 pub use crate::file::{File, FileFormat, FileSourceFile, FileSourceString, FileStoredFormat};
 pub use crate::format::Format;
 pub use crate::map::Map;
-pub use crate::source::{AsyncSource, Source};
+#[cfg(feature = "async")]
+pub use crate::source::AsyncSource;
+pub use crate::source::Source;
 pub use crate::value::{Value, ValueKind};
 
 // Re-export

src/source.rs

@@ -1,6 +1,7 @@
 use std::fmt::Debug;
 use std::str::FromStr;
 
+#[cfg(feature = "async")]
 use async_trait::async_trait;
 
 use crate::error::Result;
@@ -50,6 +51,7 @@ fn set_value(cache: &mut Value, key: &str, value: &Value) {
 /// It is advised to use `async_trait` crate while implementing this trait.
 ///
 /// See examples for sample implementation.
+#[cfg(feature = "async")]
 #[async_trait]
 pub trait AsyncSource: Debug + Sync {
     // Sync is supertrait due to https://docs.rs/async-trait/0.1.50/async_trait/index.html#dyn-traits
@@ -69,6 +71,7 @@ pub trait AsyncSource: Debug + Sync {
     }
 }
 
+#[cfg(feature = "async")]
 impl Clone for Box<dyn AsyncSource + Send + Sync> {
     fn clone(&self) -> Self {
         self.to_owned()