Document into_bits on docs.rs; use doc_cfg tags (#336)

* Use doc_cfg to tag into_bits feature

* Configure docs.rs builds to use into_bits feature and doc_cfg

Cargo.toml

@@ -11,6 +11,12 @@ license = "MIT OR Apache-2.0"
 build = "build.rs"
 edition = "2018"
 
+[package.metadata.docs.rs]
+features = ["into_bits"]
+rustdoc-args = ["--cfg", "doc_cfg"]
+# To build locally:
+# RUSTDOCFLAGS="--cfg doc_cfg" cargo +nightly doc --features into_bits --no-deps --open
+
 [badges]
 appveyor = { repository = "rust-lang/packed_simd" }
 travis-ci = { repository = "rust-lang/packed_simd" }

src/api/into_bits.rs

@@ -1,12 +1,14 @@
 //! Implementation of `FromBits` and `IntoBits`.
 
 /// Safe lossless bitwise conversion from `T` to `Self`.
+#[cfg_attr(doc_cfg, doc(cfg(feature = "into_bits")))]
 pub trait FromBits<T>: crate::marker::Sized {
  /// Safe lossless bitwise transmute from `T` to `Self`.
  fn from_bits(t: T) -> Self;
 }
 
 /// Safe lossless bitwise conversion from `Self` to `T`.
+#[cfg_attr(doc_cfg, doc(cfg(feature = "into_bits")))]
 pub trait IntoBits<T>: crate::marker::Sized {
  /// Safe lossless bitwise transmute from `self` to `T`.
  fn into_bits(self) -> T;

src/lib.rs

@@ -241,6 +241,7 @@
  clippy::from_over_into,
 )]
 #![cfg_attr(test, feature(hashmap_internals))]
+#![cfg_attr(doc_cfg, feature(doc_cfg))]
 #![deny(rust_2018_idioms, clippy::missing_inline_in_public_items)]
 #![no_std]