feat: replace write feature with std feature (#356)

* feat: replace `write` feature with `std` feature

This also implements `std::error::Error` on `CollectionAllocErr`

* docs: describe `std` feature

Cargo.toml

@@ -13,7 +13,7 @@ readme = "README.md"
 documentation = "https://docs.rs/smallvec/"
 
 [features]
-write = []
+std = []
 specialization = []
 may_dangle = []
 extract_if = []

src/lib.rs

@@ -16,16 +16,20 @@
 //!
 //! ## Optional features
 //!
-//! ### `serde`
+//! ### `std`
 //!
-//! When this optional dependency is enabled, `SmallVec` implements the `serde::Serialize` and
-//! `serde::Deserialize` traits.
+//! When this feature is enabled, traits available from `std` are implemented:
 //!
-//! ### `write`
+//! * `SmallVec<u8, _>` implements the [`std::io::Write`] trait.
+//! * [`CollectionAllocErr`] implements [`std::error::Error`].
 //!
-//! When this feature is enabled, `SmallVec<u8, _>` implements the `std::io::Write` trait.
 //! This feature is not compatible with `#![no_std]` programs.
 //!
+//! ### `serde`
+//!
+//! When this optional dependency is enabled, `SmallVec` implements the `serde::Serialize` and
+//! `serde::Deserialize` traits.
+//!
 //! ### `extract_if`
 //!
 //! **This feature is unstable.** It may change to match the unstable `extract_if` method in libstd.
@@ -62,7 +66,7 @@
 #[doc(hidden)]
 pub extern crate alloc;
 
-#[cfg(any(test, feature = "write"))]
+#[cfg(any(test, feature = "std"))]
 extern crate std;
 
 #[cfg(test)]
@@ -93,7 +97,7 @@ use serde::{
     de::{Deserialize, Deserializer, SeqAccess, Visitor},
     ser::{Serialize, SerializeSeq, Serializer},
 };
-#[cfg(feature = "write")]
+#[cfg(feature = "std")]
 use std::io;
 
 /// Error type for APIs with fallible heap allocation
@@ -113,6 +117,10 @@ impl core::fmt::Display for CollectionAllocErr {
     }
 }
 
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+impl std::error::Error for CollectionAllocErr {}
+
 /// Either a stack array with `length <= N` or a heap array
 /// whose pointer and capacity are stored here.
 ///
@@ -797,7 +805,7 @@ impl<T, const N: usize> SmallVec<T, N> {
     /// the elements `[0, at)` with its previous capacity unchanged.
     ///
     /// - If you want to take ownership of the entire contents and capacity of
-    ///   the vector, see [`mem::take`] or [`mem::replace`].
+    ///   the vector, see [`core::mem::take`] or [`core::mem::replace`].
     /// - If you don't need the returned vector at all, see [`SmallVec::truncate`].
     /// - If you want to take ownership of an arbitrary subslice, or you don't
     ///   necessarily want to store the removed items in a vector, see [`SmallVec::drain`].
@@ -2145,8 +2153,8 @@ where
     }
 }
 
-#[cfg(feature = "write")]
-#[cfg_attr(docsrs, doc(cfg(feature = "write")))]
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 impl<const N: usize> io::Write for SmallVec<u8, N> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {

src/tests.rs

@@ -924,7 +924,7 @@ fn test_resize() {
     assert_eq!(v[..], [1, 0][..]);
 }
 
-#[cfg(feature = "write")]
+#[cfg(feature = "std")]
 #[test]
 fn test_write() {
     use std::io::Write;