Enable feature(doc_cfg) during docs.rs documentation build

serde/Cargo.toml

@@ -29,7 +29,7 @@ features = ["derive", "rc"]
 [package.metadata.docs.rs]
 features = ["derive"]
 targets = ["x86_64-unknown-linux-gnu"]
-rustdoc-args = ["--generate-link-to-definition"]
+rustdoc-args = ["--cfg", "doc_cfg", "--generate-link-to-definition"]
 
 # This cfg cannot be enabled, but it still forces Cargo to keep serde_derive's
 # version in lockstep with serde's, even if someone depends on the two crates

serde/src/lib.rs

@@ -98,6 +98,8 @@
 #![doc(html_root_url = "https://docs.rs/serde/1.0.190")]
 // Support using Serde without the standard library!
 #![cfg_attr(not(feature = "std"), no_std)]
+// Show which crate feature enables conditionally compiled APIs in documentation.
+#![cfg_attr(doc_cfg, feature(doc_cfg))]
 // Unstable functionality only if the user asks for it. For tracking and
 // discussion of these features please refer to this issue:
 //