Add no_std + alloc environment 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:
@@ -74,6 +82,10 @@ matrix:
             --target thumbv6m-none-eabi
             --no-default-features
             --features nightly,cfg-target-has-atomic
+        - cargo build --manifest-path futures/Cargo.toml
+            --target thumbv6m-none-eabi
+            --no-default-features
+            --features nightly,alloc,cfg-target-has-atomic
 
     - name: cargo build --target=thumbv7m-none-eabi
       rust: nightly
@@ -84,6 +96,10 @@ matrix:
         - cargo build --manifest-path futures/Cargo.toml
             --target thumbv7m-none-eabi
             --no-default-features
+        - cargo build --manifest-path futures/Cargo.toml
+            --target thumbv7m-none-eabi
+            --no-default-features
+            --features nightly,alloc
 
     - name: cargo doc
       rust: nightly

futures-core/Cargo.toml

@@ -16,9 +16,10 @@ name = "futures_core"
 
 [features]
 default = ["std"]
-std = ["either/use_std"]
+std = ["alloc", "either/use_std"]
 nightly = []
 cfg-target-has-atomic = []
+alloc = []
 
 [dependencies]
 either = { version = "1.4", default-features = false, optional = true }

futures-core/src/future/future_obj.rs

@@ -185,10 +185,11 @@ where
     unsafe fn drop(_ptr: *mut ()) {}
 }
 
-#[cfg(feature = "std")]
-mod if_std {
+#[cfg(feature = "alloc")]
+mod if_alloc {
     use super::*;
-    use std::mem;
+    use core::mem;
+    use alloc::boxed::Box;
 
     unsafe impl<'a, T, F> UnsafeFutureObj<'a, T> for Box<F>
         where F: Future<Output = T> + 'a

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(feature = "alloc")]
+mod if_alloc {
+    use alloc::boxed::Box;
     use super::*;
+
     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 = "cfg-target-has-atomic", feature(cfg_target_has_atomic))]
+#![cfg_attr(all(feature = "alloc", not(feature = "std")), feature(alloc))]
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
@@ -12,6 +13,14 @@
 #[cfg(all(feature = "cfg-target-has-atomic", not(feature = "nightly")))]
 compile_error!("The `cfg-target-has-atomic` feature requires the `nightly` feature as an explicit opt-in to unstable features");
 
+#[cfg(all(feature = "alloc", not(any(feature = "std", feature = "nightly"))))]
+compile_error!("The `alloc` feature without `std` requires the `nightly` feature active to explicitly opt-in to unstable features");
+
+#[cfg(all(feature = "alloc", not(feature = "std")))]
+extern crate alloc;
+#[cfg(feature = "std")]
+extern crate std as alloc;
+
 pub mod future;
 #[doc(hidden)] pub use self::future::{Future, FusedFuture, TryFuture};
 

futures-core/src/stream/mod.rs

@@ -145,9 +145,9 @@ impl<S, T, E> TryStream for S
     }
 }
 
-#[cfg(feature = "std")]
-mod if_std {
-    use std::boxed::Box;
+#[cfg(feature = "alloc")]
+mod if_alloc {
+    use alloc::boxed::Box;
     use super::*;
 
     impl<S: ?Sized + Stream + Unpin> Stream for Box<S> {
@@ -161,6 +161,7 @@ mod if_std {
         }
     }
 
+    #[cfg(feature = "std")]
     impl<S: Stream> Stream for ::std::panic::AssertUnwindSafe<S> {
         type Item = S::Item;
 
@@ -172,7 +173,7 @@ mod if_std {
         }
     }
 
-    impl<T: Unpin> Stream for ::std::collections::VecDeque<T> {
+    impl<T: Unpin> Stream for ::alloc::collections::VecDeque<T> {
         type Item = T;
 
         fn poll_next(

futures-core/src/stream/stream_obj.rs

@@ -187,11 +187,11 @@ where
     unsafe fn drop(_ptr: *mut ()) {}
 }
 
-#[cfg(feature = "std")]
-mod if_std {
-    use std::boxed::Box;
-    use std::mem;
+#[cfg(feature = "alloc")]
+mod if_alloc {
     use super::*;
+    use core::mem;
+    use alloc::boxed::Box;
 
     unsafe impl<'a, T, F> UnsafeStreamObj<'a, T> for Box<F>
         where F: Stream<Item = T> + 'a

futures-sink/Cargo.toml

@@ -15,8 +15,10 @@ The asynchronous `Sink` trait for the futures-rs library.
 name = "futures_sink"
 
 [features]
-std = ["either/use_std", "futures-core-preview/std", "futures-channel-preview/std"]
+std = ["alloc", "either/use_std", "futures-core-preview/std", "futures-channel-preview/std"]
 default = ["std"]
+nightly = ["futures-core-preview/nightly"]
+alloc = ["futures-core-preview/alloc"]
 
 [dependencies]
 either = { version = "1.4", default-features = false, optional = true }

futures-sink/src/lib.rs

@@ -8,6 +8,15 @@
 #![doc(html_root_url = "https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alpha.13/futures_sink")]
 
 #![feature(futures_api)]
+#![cfg_attr(all(feature = "alloc", not(feature = "std")), feature(alloc))]
+
+#[cfg(all(feature = "alloc", not(any(feature = "std", feature = "nightly"))))]
+compile_error!("The `alloc` feature without `std` requires the `nightly` feature active to explicitly opt-in to unstable features");
+
+#[cfg(all(feature = "alloc", not(feature = "std")))]
+extern crate alloc;
+#[cfg(feature = "std")]
+extern crate std as alloc;
 
 use futures_core::task::{Waker, Poll};
 use core::pin::Pin;
@@ -155,16 +164,16 @@ impl<'a, S: ?Sized + Sink> Sink for Pin<&'a mut S> {
 #[cfg(feature = "std")]
 mod channel_impls;
 
-#[cfg(feature = "std")]
-mod if_std {
+#[cfg(feature = "alloc")]
+mod if_alloc {
     use super::*;
 
     /// The error type for `Vec` and `VecDequeue` when used as `Sink`s.
     /// Values of this type can never be created.
     #[derive(Copy, Clone, Debug)]
     pub enum VecSinkError {}
 
-    impl<T> Sink for ::std::vec::Vec<T> {
+    impl<T> Sink for ::alloc::vec::Vec<T> {
         type SinkItem = T;
         type SinkError = VecSinkError;
 
@@ -187,7 +196,7 @@ mod if_std {
         }
     }
 
-    impl<T> Sink for ::std::collections::VecDeque<T> {
+    impl<T> Sink for ::alloc::collections::VecDeque<T> {
         type SinkItem = T;
         type SinkError = VecSinkError;
 
@@ -210,7 +219,7 @@ mod if_std {
         }
     }
 
-    impl<S: ?Sized + Sink + Unpin> Sink for ::std::boxed::Box<S> {
+    impl<S: ?Sized + Sink + Unpin> Sink for ::alloc::boxed::Box<S> {
         type SinkItem = S::SinkItem;
         type SinkError = S::SinkError;
 
@@ -232,8 +241,8 @@ mod if_std {
     }
 }
 
-#[cfg(feature = "std")]
-pub use self::if_std::*;
+#[cfg(feature = "alloc")]
+pub use self::if_alloc::*;
 
 #[cfg(feature = "either")]
 use either::Either;

futures-util/Cargo.toml

@@ -15,13 +15,14 @@ Common utilities and extension traits for the futures-rs library.
 name = "futures_util"
 
 [features]
-std = ["futures-core-preview/std", "futures-io-preview/std", "futures-sink-preview/std", "futures-select-macro-preview/std", "either/use_std", "rand", "rand_core", "slab"]
+std = ["alloc", "futures-core-preview/std", "futures-io-preview/std", "futures-sink-preview/std", "futures-select-macro-preview/std", "either/use_std", "rand", "rand_core", "slab"]
 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"]
 cfg-target-has-atomic = []
+alloc = ["futures-core-preview/alloc", "futures-sink-preview/alloc"]
 
 [dependencies]
 futures-core-preview = { path = "../futures-core", version = "=0.3.0-alpha.13", default-features = false }