zcash_note_encryption: Add `doc_cfg` annotations

components/zcash_note_encryption/Cargo.toml

@@ -11,6 +11,10 @@ repository = "https://github.com/zcash/librustzcash"
 license = "MIT OR Apache-2.0"
 edition = "2018"
 
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
 [dependencies]
 blake2b_simd = { version = "0.5", default-features = false }
 byteorder = { version = "1", default-features = false }

components/zcash_note_encryption/src/lib.rs

@@ -4,6 +4,7 @@
 //! protocols.
 
 #![no_std]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 // Catch documentation errors caused by code changes.
 #![deny(broken_intra_doc_links)]
 #![deny(unsafe_code)]
@@ -29,6 +30,7 @@ use rand_core::RngCore;
 use subtle::{Choice, ConstantTimeEq};
 
 #[cfg(feature = "alloc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
 pub mod batch;
 
 pub const COMPACT_NOTE_SIZE: usize = 1 + // version
@@ -175,6 +177,7 @@ pub trait Domain {
 }
 
 #[cfg(feature = "alloc")]
+#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
 pub trait BatchDomain: Domain {
     /// Computes `Self::kdf` on a batch of items.
     ///