Show metrics feature requirement in docs.rs

Author: frigus02

Cargo.toml

@@ -18,6 +18,10 @@ exclude = [
     "README.tpl",
 ]
 
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
 [features]
 reqwest-blocking-client = ["reqwest-client"]
 reqwest-blocking-client-rustls = ["reqwest-client-rustls"]
@@ -53,9 +57,6 @@ test-case = "1.1.0"
 tokio = { version = "1.7.0", features = ["rt", "macros", "process", "time"] }
 version-sync = "0.9.2"
 
-[package.metadata.docs.rs]
-all-features = true
-
 [badges]
 github = { repository = "frigus02/opentelemetry-application-insights", workflow = "CI" }
 

src/lib.rs

@@ -206,6 +206,7 @@
 //! [`Selector`]: https://docs.rs/opentelemetry/0.16.0/opentelemetry/sdk/metrics/selectors/simple/enum.Selector.html
 #![doc(html_root_url = "https://docs.rs/opentelemetry-application-insights/0.17.0")]
 #![deny(missing_docs, unreachable_pub, missing_debug_implementations)]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 #![cfg_attr(test, deny(warnings))]
 
 mod convert;

src/metrics.rs

@@ -19,6 +19,7 @@ use opentelemetry::{
 };
 use std::convert::{TryFrom, TryInto};
 
+#[cfg_attr(docsrs, doc(cfg(feature = "metrics")))]
 impl<C> ExportKindFor for Exporter<C>
 where
     C: std::fmt::Debug,
@@ -28,6 +29,7 @@ where
     }
 }
 
+#[cfg_attr(docsrs, doc(cfg(feature = "metrics")))]
 impl<C> MetricsExporter for Exporter<C>
 where
     C: std::fmt::Debug,