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

@@ -40,6 +40,10 @@ matrix:
     - script: cargo build --no-default-features
       rust: nightly
 
+    # Ensure crate compiles with "use_alloc" instead of "use_std" (i.e. for no_std)
+    - script: cargo build --no-default-features --features use_alloc
+      rust: nightly
+
 before_install: set -e
 
 install:

Cargo.toml

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

src/buf/buf.rs

@@ -1,9 +1,12 @@
-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"))]
@@ -528,6 +531,7 @@ 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 +684,7 @@ 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

@@ -3,9 +3,9 @@ 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"))]
@@ -665,6 +665,7 @@ 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 +713,7 @@ 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/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

@@ -1,11 +1,12 @@
 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(not(feature = "use_std"))]
+use buf::Cursor;
 #[cfg(feature = "use_std")]
 use std::io::Cursor;
 
@@ -78,6 +79,7 @@ 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 +88,7 @@ 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 +115,7 @@ 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 +124,7 @@ 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

@@ -18,6 +18,7 @@
 
 mod buf;
 mod buf_mut;
+#[cfg(any(feature = "use_alloc", feature = "use_std"))]
 mod from_buf;
 mod chain;
 #[cfg(not(feature = "use_std"))]
@@ -30,6 +31,7 @@ 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"))]

src/bytes.rs

@@ -7,14 +7,15 @@ 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(not(feature = "use_std"))]
+use buf::Cursor;
 #[cfg(feature = "use_std")]
 use std::io::Cursor;
 

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};