Feature gate allocator-dependent features on "use_alloc" or "use_std"

Flags anything dependent on an allocator behind a feature gate, ensuring the
library still compiles without default features (although it may not be very
useful)

Adds "use_alloc" to obtain things like Box, String, and Vec from liballoc.

.travis.yml

@@ -37,7 +37,13 @@ matrix:
     - env: EXTRA_ARGS="--features serde"
 
     # Ensure crate compiles without default features (i.e. for no_std)
-    - script: cargo build --no-default-features
+    - env: EXTRA_ARGS="--no-default-features"
+      script: cargo build $EXTRA_ARGS
+      rust: nightly
+
+    # Ensure crate compiles with "use_alloc" instead of "use_std" (i.e. for no_std)
+    - env: EXTRA_ARGS="--no-default-features --features use_alloc"
+      script: cargo build $EXTRA_ARGS
       rust: nightly
 
 before_install: set -e

Cargo.toml

@@ -32,4 +32,5 @@ serde_test = "1.0"
 
 [features]
 default = ["use_std"]
+use_alloc = []
 use_std = ["iovec"]

src/buf/buf.rs

@@ -1,15 +1,15 @@
-use super::{IntoBuf, Take, Reader, Iter, FromBuf, Chain};
+use super::{IntoBuf, Take, Reader, Iter, Chain};
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
+use super::FromBuf;
+
 use byteorder::ByteOrder;
 #[cfg(feature = "use_std")]
 use iovec::IoVec;
 
-#[cfg(not(feature = "use_std"))]
+#[cfg(feature = "use_alloc")]
 use alloc::boxed::Box;
 use core::{cmp, ptr};
-#[cfg(not(feature = "use_std"))]
 use buf::Cursor;
-#[cfg(feature = "use_std")]
-use std::io::Cursor;
 
 /// Read bytes from a buffer.
 ///
@@ -528,6 +528,7 @@ pub trait Buf {
     ///
     /// assert_eq!(vec, &b"hello world"[..]);
     /// ```
+    #[cfg(any(feature = "use_alloc", feature = "use_std"))]
     fn collect<B>(self) -> B
         where Self: Sized,
               B: FromBuf,
@@ -680,6 +681,7 @@ impl<'a, T: Buf + ?Sized> Buf for &'a mut T {
     }
 }
 
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 impl<T: Buf + ?Sized> Buf for Box<T> {
     fn remaining(&self) -> usize {
         (**self).remaining()

src/buf/buf_mut.rs

@@ -3,15 +3,12 @@ use byteorder::ByteOrder;
 #[cfg(feature = "use_std")]
 use iovec::IoVec;
 
-#[cfg(not(feature = "use_std"))]
+#[cfg(feature = "use_alloc")]
 use alloc::boxed::Box;
-#[cfg(not(feature = "use_std"))]
+#[cfg(feature = "use_alloc")]
 use alloc::vec::Vec;
 use core::{cmp, ptr, usize};
-#[cfg(not(feature = "use_std"))]
 use buf::Cursor;
-#[cfg(feature = "use_std")]
-use std::io::Cursor;
 
 /// A trait for values that provide sequential write access to bytes.
 ///
@@ -665,6 +662,7 @@ impl<'a, T: BufMut + ?Sized> BufMut for &'a mut T {
     }
 }
 
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 impl<T: BufMut + ?Sized> BufMut for Box<T> {
     fn remaining_mut(&self) -> usize {
         (**self).remaining_mut()
@@ -712,6 +710,7 @@ impl<T: AsMut<[u8]> + AsRef<[u8]>> BufMut for Cursor<T> {
     }
 }
 
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 impl BufMut for Vec<u8> {
     #[inline]
     fn remaining_mut(&self) -> usize {

src/buf/cursor.rs

@@ -8,6 +8,9 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[cfg(feature = "use_std")]
+pub use std::io::Cursor;
+
 /// A `Cursor` wraps another type and provides it with a
 /// [`Seek`] implementation.
 ///
@@ -18,12 +21,14 @@
 /// The standard library implements some I/O traits on various types which
 /// are commonly used as a buffer, like `Cursor<`[`Vec`]`<u8>>` and
 /// `Cursor<`[`&[u8]`][bytes]`>`.
+#[cfg(not(feature = "use_std"))]
 #[derive(Clone, Debug)]
 pub struct Cursor<T> {
     inner: T,
     pos: u64,
 }
 
+#[cfg(not(feature = "use_std"))]
 impl<T> Cursor<T> {
     /// Creates a new cursor wrapping the provided underlying I/O object.
     ///
@@ -34,9 +39,6 @@ impl<T> Cursor<T> {
         Cursor { pos: 0, inner: inner }
     }
 
-    /// Consumes this cursor, returning the underlying value.
-    pub fn into_inner(self) -> T { self.inner }
-
     /// Gets a reference to the underlying value in this cursor.
     pub fn get_ref(&self) -> &T { &self.inner }
 

src/buf/from_buf.rs

@@ -1,6 +1,6 @@
 use {Buf, BufMut, IntoBuf, Bytes, BytesMut};
 
-#[cfg(not(feature = "use_std"))]
+#[cfg(feature = "use_alloc")]
 use alloc::vec::Vec;
 
 /// Conversion from a [`Buf`]

src/buf/into_buf.rs

@@ -1,13 +1,11 @@
 use super::{Buf};
 
-#[cfg(not(feature = "use_std"))]
-use buf::Cursor;
-#[cfg(not(feature = "use_std"))]
+#[cfg(feature = "use_alloc")]
 use alloc::string::String;
-#[cfg(not(feature = "use_std"))]
+#[cfg(feature = "use_alloc")]
 use alloc::vec::Vec;
-#[cfg(feature = "use_std")]
-use std::io::Cursor;
+
+use buf::Cursor;
 
 /// Conversion into a `Buf`
 ///
@@ -78,6 +76,7 @@ impl<'a> IntoBuf for &'a str {
     }
 }
 
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 impl IntoBuf for Vec<u8> {
     type Buf = Cursor<Vec<u8>>;
 
@@ -86,6 +85,7 @@ impl IntoBuf for Vec<u8> {
     }
 }
 
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 impl<'a> IntoBuf for &'a Vec<u8> {
     type Buf = Cursor<&'a [u8]>;
 
@@ -112,6 +112,7 @@ impl<'a> IntoBuf for &'a &'static str {
     }
 }
 
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 impl IntoBuf for String {
     type Buf = Cursor<Vec<u8>>;
 
@@ -120,6 +121,7 @@ impl IntoBuf for String {
     }
 }
 
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 impl<'a> IntoBuf for &'a String {
     type Buf = Cursor<&'a [u8]>;
 

src/buf/mod.rs

@@ -18,9 +18,9 @@
 
 mod buf;
 mod buf_mut;
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 mod from_buf;
 mod chain;
-#[cfg(not(feature = "use_std"))]
 mod cursor;
 mod into_buf;
 mod iter;
@@ -30,9 +30,9 @@ mod writer;
 
 pub use self::buf::Buf;
 pub use self::buf_mut::BufMut;
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 pub use self::from_buf::FromBuf;
 pub use self::chain::Chain;
-#[cfg(not(feature = "use_std"))]
 pub use self::cursor::Cursor;
 pub use self::into_buf::IntoBuf;
 pub use self::iter::Iter;

src/bytes.rs

@@ -7,16 +7,14 @@ use core::borrow::Borrow;
 use core::sync::atomic::{self, AtomicUsize, AtomicPtr};
 use core::sync::atomic::Ordering::{Relaxed, Acquire, Release, AcqRel};
 
-#[cfg(not(feature = "use_std"))]
-use buf::Cursor;
-#[cfg(not(feature = "use_std"))]
+#[cfg(feature = "use_alloc")]
 use alloc::boxed::Box;
-#[cfg(not(feature = "use_std"))]
+#[cfg(feature = "use_alloc")]
 use alloc::string::String;
-#[cfg(not(feature = "use_std"))]
+#[cfg(feature = "use_alloc")]
 use alloc::vec::Vec;
-#[cfg(feature = "use_std")]
-use std::io::Cursor;
+
+use buf::Cursor;
 
 /// A reference counted contiguous slice of memory.
 ///

src/lib.rs

@@ -71,11 +71,11 @@
 #![deny(warnings, missing_docs, missing_debug_implementations)]
 #![doc(html_root_url = "https://docs.rs/bytes/0.4")]
 #![cfg_attr(not(feature = "use_std"), no_std)]
-#![cfg_attr(not(feature = "use_std"), feature(alloc))]
+#![cfg_attr(feature = "use_alloc", feature(alloc))]
 
 extern crate byteorder;
 
-#[cfg(not(feature = "use_std"))]
+#[cfg(feature = "use_alloc")]
 extern crate alloc;
 #[cfg(feature = "use_std")]
 extern crate core;
@@ -96,8 +96,12 @@ pub use buf::{
     Take,
 };
 
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 mod bytes;
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 mod debug;
+
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 pub use bytes::{Bytes, BytesMut};
 
 pub use byteorder::{ByteOrder, BigEndian, LittleEndian};