Mark AsyncConfigBuilder deprecated

Signed-off-by: Ian Jackson <[email protected]>
Signed-off-by: Matthias Beyer <[email protected]>

Author: ijackson

src/builder.rs

@@ -113,6 +113,7 @@ pub struct DefaultState {
 //
 // In a future release, we should have
 //    type AsyncConfigBuilder = ConfigBuilder<AsyncState>;
+#[deprecated = "AsyncConfigBuilder is useless.  Use ConfigBuilder<AsyncState>"]
 #[doc(hidden)]
 #[derive(Debug, Clone, Default)]
 pub struct AsyncConfigBuilder {}

src/lib.rs

@@ -33,7 +33,7 @@ mod ser;
 mod source;
 mod value;
 
-pub use crate::builder::{AsyncConfigBuilder, ConfigBuilder};
+pub use crate::builder::ConfigBuilder;
 pub use crate::config::Config;
 pub use crate::env::Environment;
 pub use crate::error::ConfigError;
@@ -46,6 +46,9 @@ pub use crate::source::AsyncSource;
 pub use crate::source::Source;
 pub use crate::value::{Value, ValueKind};
 
+#[allow(deprecated)]
+pub use crate::builder::AsyncConfigBuilder;
+
 // Re-export
 #[cfg(feature = "convert-case")]
 pub use convert_case::Case;