Add no_std + alloc support

Author: taiki-e

.travis.yml

@@ -54,6 +54,14 @@ matrix:
         - cargo build --manifest-path futures-sink/Cargo.toml --no-default-features
         - cargo build --manifest-path futures-util/Cargo.toml --no-default-features
 
+    - name: cargo build (alloc)
+      rust: nightly
+      script:
+        - cargo build --manifest-path futures/Cargo.toml --no-default-features --features=alloc,nightly
+        - cargo build --manifest-path futures-core/Cargo.toml --no-default-features --features=alloc,nightly
+        - cargo build --manifest-path futures-sink/Cargo.toml --no-default-features --features=alloc,nightly
+        - cargo build --manifest-path futures-util/Cargo.toml --no-default-features --features=alloc,nightly
+
     - name: cargo build (default features)
       rust: nightly
       script:

futures-core/Cargo.toml

@@ -10,6 +10,7 @@ documentation = "https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alph
 description = """
 The core traits and types in for the `futures` library.
 """
+build = "build.rs"
 
 [lib]
 name = "futures_core"
@@ -18,9 +19,11 @@ name = "futures_core"
 default = ["std"]
 std = ["either/use_std"]
 nightly = []
+alloc = ["alloc-shim/alloc"]
 
 [dependencies]
 either = { version = "1.4", default-features = false, optional = true }
+alloc-shim = { version = "0.2.1", optional = true }
 
 [dev-dependencies]
 futures-preview = { path = "../futures", version = "=0.3.0-alpha.12" }

futures-core/build.rs

@@ -0,0 +1,9 @@
+use std::env;
+
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
+    if env::var_os("CARGO_FEATURE_STD").is_some() || env::var_os("CARGO_FEATURE_ALLOC").is_some() {
+        println!("cargo:rustc-cfg=alloc");
+    }
+}

futures-core/src/future/future_obj.rs

@@ -185,9 +185,10 @@ where
     unsafe fn drop(_ptr: *mut ()) {}
 }
 
-#[cfg(feature = "std")]
-mod if_std {
+#[cfg(alloc)]
+mod if_alloc {
     use super::*;
+    use std::boxed::Box;
     use std::mem;
 
     unsafe impl<'a, T, F> UnsafeFutureObj<'a, T> for Box<F>

futures-core/src/future/mod.rs

@@ -33,9 +33,11 @@ impl<F: FusedFuture + ?Sized> FusedFuture for &mut F {
     }
 }
 
-#[cfg(feature = "std")]
-mod if_std {
+#[cfg(alloc)]
+mod if_alloc {
     use super::*;
+    use std::boxed::Box;
+
     impl<F: FusedFuture + ?Sized> FusedFuture for Box<F> {
         fn is_terminated(&self) -> bool {
             <F as FusedFuture>::is_terminated(&**self)
@@ -48,6 +50,7 @@ mod if_std {
         }
     }
 
+    #[cfg(feature = "std")]
     impl<F: FusedFuture> FusedFuture for std::panic::AssertUnwindSafe<F> {
         fn is_terminated(&self) -> bool {
             <F as FusedFuture>::is_terminated(&**self)

futures-core/src/lib.rs

@@ -2,6 +2,7 @@
 
 #![feature(futures_api)]
 #![cfg_attr(feature = "nightly", feature(cfg_target_has_atomic))]
+#![cfg_attr(feature = "alloc", feature(alloc))]
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
@@ -10,6 +11,12 @@
 
 #![doc(html_root_url = "https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alpha.12/futures_core")]
 
+#[cfg(all(feature = "alloc", not(feature = "nightly")))]
+compile_error!("The `alloc` feature requires the `nightly` feature active to explicitly opt-in to unstable features");
+
+#[cfg(all(feature = "alloc", not(feature = "std")))]
+extern crate alloc as std;
+
 pub mod future;
 #[doc(hidden)] pub use self::future::{Future, FusedFuture, TryFuture};
 

futures-core/src/stream/mod.rs

@@ -145,8 +145,8 @@ impl<S, T, E> TryStream for S
     }
 }
 
-#[cfg(feature = "std")]
-mod if_std {
+#[cfg(alloc)]
+mod if_alloc {
     use std::boxed::Box;
     use super::*;
 
@@ -161,6 +161,7 @@ mod if_std {
         }
     }
 
+    #[cfg(feature = "std")]
     impl<S: Stream> Stream for ::std::panic::AssertUnwindSafe<S> {
         type Item = S::Item;
 

futures-core/src/stream/stream_obj.rs

@@ -2,7 +2,6 @@ use super::Stream;
 use crate::task::{LocalWaker, Poll};
 use core::fmt;
 use core::marker::PhantomData;
-use core::mem;
 use core::pin::Pin;
 
 /// A custom trait object for polling streams, roughly akin to
@@ -188,10 +187,11 @@ where
     unsafe fn drop(_ptr: *mut ()) {}
 }
 
-#[cfg(feature = "std")]
-mod if_std {
-    use std::boxed::Box;
+#[cfg(alloc)]
+mod if_alloc {
     use super::*;
+    use std::boxed::Box;
+    use std::mem;
 
     unsafe impl<'a, T, F> UnsafeStreamObj<'a, T> for Box<F>
         where F: Stream<Item = T> + 'a

futures-core/src/task/mod.rs

@@ -6,5 +6,5 @@ pub mod __internal;
 pub use self::spawn::{Spawn, LocalSpawn, SpawnError};
 
 pub use core::task::{Poll, Waker, LocalWaker, UnsafeWake};
-#[cfg(feature = "std")]
+#[cfg(alloc)]
 pub use std::task::{Wake, local_waker, local_waker_from_nonlocal};

futures-sink/Cargo.toml

@@ -10,15 +10,19 @@ documentation = "https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alph
 description = """
 The asynchronous `Sink` trait for the futures-rs library.
 """
+build = "build.rs"
 
 [lib]
 name = "futures_sink"
 
 [features]
 std = ["either/use_std", "futures-core-preview/std", "futures-channel-preview/std"]
 default = ["std"]
+nightly = ["futures-core-preview/nightly"]
+alloc = ["futures-core-preview/alloc", "alloc-shim/alloc"]
 
 [dependencies]
 either = { version = "1.4", default-features = false, optional = true }
 futures-core-preview = { path = "../futures-core", version = "=0.3.0-alpha.12", default-features = false }
 futures-channel-preview = { path = "../futures-channel", version = "=0.3.0-alpha.12", default-features = false }
+alloc-shim = { version = "0.2.1", optional = true }

futures-sink/build.rs

@@ -0,0 +1,9 @@
+use std::env;
+
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
+    if env::var_os("CARGO_FEATURE_STD").is_some() || env::var_os("CARGO_FEATURE_ALLOC").is_some() {
+        println!("cargo:rustc-cfg=alloc");
+    }
+}

futures-sink/src/lib.rs

@@ -8,6 +8,13 @@
 #![doc(html_root_url = "https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alpha.12/futures_sink")]
 
 #![feature(futures_api)]
+#![cfg_attr(feature = "alloc", feature(alloc))]
+
+#[cfg(all(feature = "alloc", not(feature = "nightly")))]
+compile_error!("The `alloc` feature requires the `nightly` feature active to explicitly opt-in to unstable features");
+
+#[cfg(all(feature = "alloc", not(feature = "std")))]
+extern crate alloc as std;
 
 use futures_core::task::{LocalWaker, Poll};
 use core::pin::Pin;
@@ -155,8 +162,8 @@ impl<'a, S: ?Sized + Sink> Sink for Pin<&'a mut S> {
 #[cfg(feature = "std")]
 mod channel_impls;
 
-#[cfg(feature = "std")]
-mod if_std {
+#[cfg(alloc)]
+mod if_alloc {
     use super::*;
 
     /// The error type for `Vec` and `VecDequeue` when used as `Sink`s.
@@ -232,8 +239,8 @@ mod if_std {
     }
 }
 
-#[cfg(feature = "std")]
-pub use self::if_std::*;
+#[cfg(alloc)]
+pub use self::if_alloc::*;
 
 #[cfg(feature = "either")]
 use either::Either;

futures-util/Cargo.toml

@@ -10,6 +10,7 @@ documentation = "https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alph
 description = """
 Common utilities and extension traits for the futures-rs library.
 """
+build = "build.rs"
 
 [lib]
 name = "futures_util"
@@ -20,7 +21,8 @@ default = ["std", "futures-core-preview/either", "futures-sink-preview/either"]
 compat = ["std", "futures_01"]
 io-compat = ["compat", "tokio-io"]
 bench = []
-nightly = []
+nightly = ["futures-core-preview/nightly", "futures-sink-preview/nightly"]
+alloc = ["futures-core-preview/alloc", "futures-sink-preview/alloc", "alloc-shim/alloc"]
 
 [dependencies]
 futures-core-preview = { path = "../futures-core", version = "=0.3.0-alpha.12", default-features = false }
@@ -37,6 +39,7 @@ slab = { version = "0.4", optional = true }
 futures_01 = { version = "0.1.25", optional = true, package = "futures" }
 tokio-io = { version = "0.1.9", optional = true }
 pin-utils = "0.1.0-alpha.4"
+alloc-shim = { version = "0.2.1", optional = true }
 
 [dev-dependencies]
 futures-preview = { path = "../futures", version = "=0.3.0-alpha.12" }

futures-util/build.rs

@@ -0,0 +1,9 @@
+use std::env;
+
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
+    if env::var_os("CARGO_FEATURE_STD").is_some() || env::var_os("CARGO_FEATURE_ALLOC").is_some() {
+        println!("cargo:rustc-cfg=alloc");
+    }
+}

futures-util/src/future/mod.rs

@@ -7,6 +7,8 @@ use core::pin::Pin;
 use futures_core::future::Future;
 use futures_core::stream::Stream;
 use futures_core::task::{LocalWaker, Poll};
+#[cfg(alloc)]
+use std::boxed::Box;
 
 // re-export for `select!`
 #[doc(hidden)]
@@ -67,9 +69,9 @@ pub use self::unit_error::UnitError;
 mod chain;
 pub(crate) use self::chain::Chain;
 
-#[cfg(feature = "std")]
+#[cfg(alloc)]
 mod abortable;
-#[cfg(feature = "std")]
+#[cfg(alloc)]
 pub use self::abortable::{abortable, Abortable, AbortHandle, AbortRegistration, Aborted};
 
 #[cfg(feature = "std")]
@@ -82,10 +84,10 @@ mod remote_handle;
 #[cfg(feature = "std")]
 pub use self::remote_handle::{Remote, RemoteHandle};
 
-#[cfg(feature = "std")]
+#[cfg(alloc)]
 mod join_all;
 
-#[cfg(feature = "std")]
+#[cfg(alloc)]
 pub use self::join_all::{join_all, JoinAll};
 
 // #[cfg(feature = "std")]
@@ -653,7 +655,7 @@ pub trait FutureExt: Future {
     }
 
     /// Wrap the future in a Box, pinning it.
-    #[cfg(feature = "std")]
+    #[cfg(alloc)]
     fn boxed(self) -> Pin<Box<Self>>
         where Self: Sized
     {

futures-util/src/lib.rs

@@ -4,13 +4,20 @@
 #![feature(futures_api, box_into_pin)]
 #![cfg_attr(feature = "std", feature(async_await, await_macro))]
 #![cfg_attr(feature = "nightly", feature(cfg_target_has_atomic))]
+#![cfg_attr(feature = "alloc", feature(alloc))]
 
 #![cfg_attr(not(feature = "std"), no_std)]
 #![warn(missing_docs, missing_debug_implementations)]
 #![deny(bare_trait_objects)]
 
 #![doc(html_root_url = "https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alpha.12/futures_util")]
 
+#[cfg(all(feature = "alloc", not(feature = "nightly")))]
+compile_error!("The `alloc` feature requires the `nightly` feature active to explicitly opt-in to unstable features");
+
+#[cfg(all(feature = "alloc", not(feature = "std")))]
+extern crate alloc as std;
+
 #[macro_use]
 mod macros;
 
@@ -89,5 +96,5 @@ pub mod io;
 #[cfg(feature = "std")]
 #[doc(hidden)] pub use crate::io::{AsyncReadExt, AsyncWriteExt};
 
-#[cfg(feature = "std")]
+#[cfg(alloc)]
 pub mod lock;

futures-util/src/lock/bilock.rs

@@ -3,9 +3,11 @@
 
 use futures_core::future::Future;
 use futures_core::task::{LocalWaker, Poll, Waker};
+#[cfg(feature = "std")]
 use std::any::Any;
 use std::boxed::Box;
 use std::cell::UnsafeCell;
+#[cfg(feature = "std")]
 use std::error::Error;
 use std::fmt;
 use std::mem;
@@ -210,6 +212,7 @@ impl<T> fmt::Display for ReuniteError<T> {
     }
 }
 
+#[cfg(feature = "std")]
 impl<T: Any> Error for ReuniteError<T> {
     fn description(&self) -> &str {
         "tried to reunite two BiLocks that don't form a pair"

futures-util/src/lock/mod.rs

@@ -1,6 +1,8 @@
 //! Futures-powered synchronization primitives.
 
+#[cfg(feature = "std")]
 mod mutex;
+#[cfg(feature = "std")]
 pub use self::mutex::{Mutex, MutexLockFuture, MutexGuard};
 
 mod bilock;

futures-util/src/sink/mod.rs

@@ -41,9 +41,9 @@ pub use self::with::With;
 mod with_flat_map;
 pub use self::with_flat_map::WithFlatMap;
 
-#[cfg(feature = "std")]
+#[cfg(alloc)]
 mod buffer;
-#[cfg(feature = "std")]
+#[cfg(alloc)]
 pub use self::buffer::Buffer;
 
 impl<T: ?Sized> SinkExt for T where T: Sink {}
@@ -156,7 +156,7 @@ pub trait SinkExt: Sink {
     ///
     /// This method is only available when the `std` feature of this
     /// library is activated, and it is activated by default.
-    #[cfg(feature = "std")]
+    #[cfg(alloc)]
     fn buffer(self, capacity: usize) -> Buffer<Self>
         where Self: Sized,
     {