From ab194c2cfa5d99f61d40965a72c6917b43923175 Mon Sep 17 00:00:00 2001
From: Ashley Mannix <kodraus@hey.com>
Date: Sun, 31 Oct 2021 09:42:28 +1000
Subject: [PATCH] add unstable zerocopy support

---
 .github/workflows/ci.yml |  5 +++++
 Cargo.toml               |  8 ++++++++
 README.md                | 16 ++++++++++++++++
 src/lib.rs               | 26 +++++++++++++++++++++++++-
 4 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5d07b54b..418e0ee8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -12,6 +12,9 @@ jobs:
   os_tests:
     name: "Tests / OS: ${{ matrix.os }} - ${{ matrix.channel }}-${{ matrix.rust_target }}"
     runs-on: ${{ matrix.os }}
+    env:
+      RUSTFLAGS: "--cfg uuid_unstable"
+      RUSTDOCFLAGS: "--cfg uuid_unstable"
     strategy:
       matrix:
         exclude:
@@ -122,6 +125,8 @@ jobs:
   nodeps:
     name: Build / No deps
     runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: "--cfg uuid_unstable"
     steps:
       - name: Checkout sources
         uses: actions/checkout@v2
diff --git a/Cargo.toml b/Cargo.toml
index 4c01df72..0fb1cc39 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -61,6 +61,9 @@ v4 = ["getrandom"]
 v5 = ["sha-1"]
 js = ["getrandom", "getrandom/js"]
 
+# Unstable features (these also need RUSTFLAGS="--cfg uuid_unstable" to work)
+zerocopy-unstable = ["zerocopy"]
+
 # Private
 [dependencies.getrandom]
 optional = true
@@ -100,6 +103,11 @@ version = "2"
 optional = true
 version = "0.3"
 
+# Public (unstable): Used in `zerocopy` derive
+[dependencies.zerocopy]
+optional = true
+version = "0.6"
+
 [dev-dependencies.bincode]
 version = "1.0"
 
diff --git a/README.md b/README.md
index 754245a2..0e9359ff 100644
--- a/README.md
+++ b/README.md
@@ -76,6 +76,22 @@ You can disable default features with:
 uuid = { version = "0.8", default-features = false }
 ```
 
+### Unstable features
+
+Some features are unstable. They may be incomplete or depend on other unstable libraries.
+These include:
+
+* `zerocopy-unstable` - adds support for zero-copy deserialization using the `zerocopy` library.
+
+Unstable features may break between minor releases.
+
+To allow unstable features, you'll need to enable the Cargo feature as normal, but also pass an additional
+flag through your environment to opt-in to unstable `uuid` features:
+
+```
+RUSTFLAGS="--cfg uuid_unstable"
+```
+
 ## Examples
 
 To parse a UUID given in the simple format and print it as a urn:
diff --git a/src/lib.rs b/src/lib.rs
index a8e1d651..4e1af4cc 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -64,6 +64,22 @@
 //! uuid = { version = "0.8", default-features = false }
 //! ```
 //!
+//! ## Unstable features
+//!
+//! Some features are unstable. They may be incomplete or depend on other unstable libraries.
+//! These include:
+//!
+//! * `zerocopy-unstable` - adds support for zero-copy deserialization using the `zerocopy` library.
+//!
+//! Unstable features may break between minor releases.
+//!
+//! To allow unstable features, you'll need to enable the Cargo feature as normal, but also pass an additional
+//! flag through your environment to opt-in to unstable `uuid` features:
+//!
+//! ```text
+//! RUSTFLAGS="--cfg uuid_unstable"
+//! ```
+//!
 //! # Building for other targets
 //!
 //! ## WebAssembly
@@ -96,7 +112,7 @@
 //!
 //! If you need to use `v4` in a no-std environment, you'll need to
 //! follow [`getrandom`'s docs] on configuring a source of randomness
-//! on unsupported targets.
+//! on currently unsupported targets.
 //!
 //! # Examples
 //!
@@ -188,6 +204,13 @@ extern crate std;
 #[macro_use]
 extern crate core as std;
 
+// Check that unstable features are accompanied by a the `uuid_unstable` cfg
+#[cfg(all(not(uuid_unstable), feature = "zerocopy-unstable"))]
+compile_error!("The `zerocopy-unstable` feature is unstable and may break between releases. Please also pass `RUSTFLAGS=\"--cfg uuid_unstable\"` to allow it.");
+
+#[cfg(feature = "zerocopy-unstable")]
+use zerocopy::{AsBytes, FromBytes, Unaligned};
+
 mod builder;
 mod error;
 mod parser;
@@ -248,6 +271,7 @@ pub enum Variant {
 
 /// A Universally Unique Identifier (UUID).
 #[derive(Clone, Copy, Eq, Hash, Ord, PartialEq, PartialOrd)]
+#[cfg_attr(feature = "zerocopy-unstable", derive(AsBytes, FromBytes, Unaligned))]
 #[repr(transparent)]
 pub struct Uuid(Bytes);