multiboot2-header: add unstable feature

Author: phip1611

multiboot2-header/Cargo.toml

@@ -35,6 +35,8 @@ required-features = ["builder"]
 default = ["builder"]
 alloc = []
 builder = ["alloc"]
+# Nightly-only features, which will eventually be stabilized.
+unstable = []
 
 [dependencies]
 # used for MBI tags

multiboot2-header/Changelog.md

@@ -3,6 +3,8 @@
 ## Unreleased
 - MSRV is 1.56.1
 - renamed the `std` feature to `alloc`
+- added the optional `unstable` feature (requires nightly)
+  - implement `core::error::Error` for `LoadError`
 
 ## v0.2.0 (2022-05-03)
 - **BREAKING** renamed `EntryHeaderTag` to `EntryAddressHeaderTag`

multiboot2-header/src/header.rs

@@ -5,7 +5,7 @@ use crate::{
     RelocatableHeaderTag,
 };
 use core::convert::TryInto;
-use core::fmt::{Debug, Formatter};
+use core::fmt::{Debug, Display, Formatter};
 use core::mem::size_of;
 
 /// Magic value for a [`Multiboot2Header`], as defined in spec.
@@ -212,6 +212,15 @@ pub enum LoadError {
     TooSmall,
 }
 
+impl Display for LoadError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+        write!(f, "{:?}", self)
+    }
+}
+
+#[cfg(feature = "unstable")]
+impl core::error::Error for LoadError {}
+
 /// **Use this only if you know what you do. You probably want to use
 /// [`Multiboot2Header`] instead.**
 ///

multiboot2-header/src/lib.rs

@@ -34,6 +34,7 @@
 //! The MSRV is 1.56.1 stable.
 
 #![no_std]
+#![cfg_attr(feature = "unstable", feature(error_in_core))]
 #![deny(rustdoc::all)]
 #![deny(clippy::all)]
 #![deny(clippy::missing_const_for_fn)]
@@ -77,6 +78,5 @@ pub use self::relocatable::*;
 pub use self::tags::*;
 pub use self::uefi_bs::*;
 
-/// Re-export of [`multiboot2::TagType`] from `multiboot2`-crate as `MbiTagType`, i.e. tags that
-/// describe the entries in the Multiboot2 Information Structure (MBI).
+/// Re-export of [`multiboot2::TagType`] from `multiboot2`-crate.
 pub use multiboot2::TagType as MbiTagType;

multiboot2/Cargo.toml

@@ -36,7 +36,7 @@ documentation = "https://docs.rs/multiboot2"
 default = ["builder"]
 alloc = []
 builder = ["alloc"]
-# Nightly-only features that will eventually be stabilized.
+# Nightly-only features, which will eventually be stabilized.
 unstable = []
 
 [dependencies]