0.3 backports

.github/workflows/ci.yml

@@ -43,7 +43,7 @@ jobs:
       matrix:
         rust:
           # This is the minimum Rust version supported by futures-core, futures-io, futures-sink, futures-task, futures-channel.
-          # When updating this, the reminder to update the minimum required version of `async-await` feature in README.md.
+          # When updating this, the reminder to update the minimum required version in .clippy.toml.
           - 1.36.0
     runs-on: ubuntu-latest
     steps:
@@ -74,8 +74,8 @@ jobs:
       matrix:
         rust:
           # This is the minimum Rust version supported by futures, futures-util, futures-macro, futures-executor, futures-test.
-          # When updating this, the reminder to update the minimum required version of `async-await` feature in README.md.
-          - 1.37.0
+          # When updating this, the reminder to update the minimum required version in README.md.
+          - 1.41.0
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
@@ -84,6 +84,8 @@ jobs:
       - run: cargo +stable install cargo-hack
       # remove dev-dependencies to avoid https://github.com/rust-lang/cargo/issues/4866
       - run: cargo hack --remove-dev-deps --workspace
+      # Check default features
+      - run: cargo hack build --workspace --ignore-private
       # Check no-default-features
       - run: cargo hack build --workspace --exclude futures-test --ignore-private --no-default-features
       # Check alloc feature
@@ -95,22 +97,6 @@ jobs:
       # Check thread-pool feature (futures, futures-executor)
       - run: cargo hack build -p futures -p futures-executor --no-default-features --features std,thread-pool
 
-  async-await-msrv:
-    name: cargo +${{ matrix.rust }} build
-    strategy:
-      matrix:
-        rust:
-          # This is the minimum Rust version supported by `async-await` feature.
-          # When updating this, the reminder to update the minimum required version of `async-await` feature in README.md.
-          - 1.39.0
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - name: Install Rust
-        run: rustup update ${{ matrix.rust }} && rustup default ${{ matrix.rust }}
-      - run: cargo +stable install cargo-hack
-      - run: cargo hack build --workspace --no-dev-deps
-
   build:
     name: cargo +${{ matrix.rust }} build
     strategy:
@@ -141,59 +127,41 @@ jobs:
       - run: cargo update -Z minimal-versions
       - run: cargo build --workspace --all-features
 
-  thumbv6m:
-    name: cargo build --target thumbv6m-none-eabi
+  no-std:
+    name: cargo build --target ${{ matrix.target }}
+    strategy:
+      matrix:
+        target:
+          - thumbv6m-none-eabi
+          - thumbv7m-none-eabi
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
       - name: Install Rust
         run: rustup update nightly && rustup default nightly
-      - run: rustup target add thumbv6m-none-eabi
+      - run: rustup target add ${{ matrix.target }}
       - run: cargo install cargo-hack
       # remove dev-dependencies to avoid https://github.com/rust-lang/cargo/issues/4866
       - run: cargo hack --remove-dev-deps --workspace
       - run: |
-          cargo build --manifest-path futures/Cargo.toml \
-            --target thumbv6m-none-eabi \
-            --no-default-features \
-            --features unstable,cfg-target-has-atomic
-      - run: |
-          cargo build --manifest-path futures/Cargo.toml \
-            --target thumbv6m-none-eabi \
-            --no-default-features \
-            --features alloc,unstable,cfg-target-has-atomic
-      - run: |
-          cargo build --manifest-path futures/Cargo.toml \
-            --target thumbv6m-none-eabi \
-            --no-default-features \
-            --features async-await,unstable,cfg-target-has-atomic
-
-  thumbv7m:
-    name: cargo build --target thumbv7m-none-eabi
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - name: Install Rust
-        run: rustup update nightly && rustup default nightly
-      - run: rustup target add thumbv7m-none-eabi
-      - run: cargo install cargo-hack
-      # remove dev-dependencies to avoid https://github.com/rust-lang/cargo/issues/4866
-      - run: cargo hack --remove-dev-deps --workspace
+          cargo hack build --manifest-path futures/tests/no-std/Cargo.toml \
+            --each-feature --optional-deps \
+            --target ${{ matrix.target }}
       - run: |
-          cargo build --manifest-path futures/Cargo.toml \
-            --target thumbv7m-none-eabi \
+          cargo hack build --workspace --ignore-private \
+            --exclude futures-test --exclude futures-macro \
             --no-default-features \
-            --features unstable,cfg-target-has-atomic
+            --target ${{ matrix.target }}
       - run: |
-          cargo build --manifest-path futures/Cargo.toml \
-            --target thumbv7m-none-eabi \
-            --no-default-features \
-            --features alloc
+          cargo hack build --workspace --ignore-private \
+            --exclude futures-test --exclude futures-macro \
+            --no-default-features --features alloc --ignore-unknown-features \
+            --target ${{ matrix.target }}
       - run: |
-          cargo build --manifest-path futures/Cargo.toml \
-            --target thumbv7m-none-eabi \
-            --no-default-features \
-            --features async-await
+          cargo hack build --workspace --ignore-private \
+            --exclude futures-test --exclude futures-macro \
+            --no-default-features --features async-await,alloc --ignore-unknown-features \
+            --target ${{ matrix.target }}
 
   bench:
     name: cargo bench
@@ -226,6 +194,19 @@ jobs:
             --workspace --exclude futures-test \
             --features unstable --ignore-unknown-features
 
+  # When this job failed, run ci/no_atomic_cas.sh and commit result changes.
+  # TODO(taiki-e): Ideally, this should be automated using a bot that creates
+  #                PR when failed, but there is no bandwidth to implement it
+  #                right now...
+  codegen:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install Rust
+        run: rustup update nightly && rustup default nightly
+      - run: ci/no_atomic_cas.sh
+      - run: git diff --exit-code
+
   san:
     name: cargo test -Z sanitizer=${{ matrix.sanitizer }}
     strategy:
@@ -247,18 +228,28 @@ jobs:
           # `--cfg futures_sanitizer`.
           RUSTFLAGS: -D warnings -Z sanitizer=${{ matrix.sanitizer }} --cfg futures_sanitizer
 
-  clippy:
-    name: cargo clippy
+  # This branch no longer actively developed. Most commits to this
+  # branch are backporting and should not be blocked by clippy.
+  # clippy:
+  #   name: cargo clippy
+  #   runs-on: ubuntu-latest
+  #   steps:
+  #     - uses: actions/checkout@v2
+  #     - name: Install Rust and Clippy
+  #       run: |
+  #         toolchain=nightly-$(curl -sSf https://rust-lang.github.io/rustup-components-history/x86_64-unknown-linux-gnu/clippy)
+  #         rustup set profile minimal
+  #         rustup default "$toolchain"
+  #         rustup component add clippy
+  #     - run: cargo clippy --workspace --all-features --all-targets
+
+  fmt:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - name: Install Rust and Clippy
-        run: |
-          toolchain=nightly-$(curl -sSf https://rust-lang.github.io/rustup-components-history/x86_64-unknown-linux-gnu/clippy)
-          rustup set profile minimal
-          rustup default "$toolchain"
-          rustup component add clippy
-      - run: cargo clippy --workspace --all-features --all-targets
+      - name: Install Rust
+        run: rustup update stable && rustup default stable
+      - run: tools/fmt.sh
 
   docs:
     name: cargo doc

.rustfmt.toml

@@ -1 +1,2 @@
 use_small_heuristics = "Max"
+edition = "2018"

Cargo.toml

@@ -13,6 +13,7 @@ members = [
 
   "futures/tests/macro-tests",
   "futures/tests/macro-reexport",
+  "futures/tests/no-std",
 
   "examples/functional",
   "examples/imperative",

README.md

@@ -15,8 +15,8 @@
     <img alt="Crates.io" src="https://img.shields.io/crates/v/futures.svg">
   </a>
 
-  <a href="https://blog.rust-lang.org/2019/11/07/Rust-1.39.0.html">
-    <img alt="Rustc Version" src="https://img.shields.io/badge/rustc-1.39+-lightgray.svg">
+  <a href="https://www.rust-lang.org">
+    <img alt="Rustc Version" src="https://img.shields.io/badge/rustc-1.41+-lightgray.svg">
   </a>
 </p>
 
@@ -48,7 +48,7 @@ Now, you can use futures-rs:
 use futures::future::Future;
 ```
 
-The current futures-rs requires Rust 1.39 or later.
+The current futures-rs requires Rust 1.41 or later.
 
 ### Feature `std`
 

ci/no_atomic_cas.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+
+set -euo pipefail
+IFS=$'\n\t'
+
+cd "$(cd "$(dirname "$0")" && pwd)"/..
+
+file="no_atomic_cas.rs"
+
+{
+    echo "// This file is @generated by $(basename "$0")."
+    echo "// It is not intended for manual editing."
+    echo ""
+    echo "const NO_ATOMIC_CAS_TARGETS: &[&str] = &["
+} >"$file"
+
+for target in $(rustc --print target-list); do
+    res=$(rustc --print target-spec-json -Z unstable-options --target "$target" \
+        | jq -r "select(.\"atomic-cas\" == false)")
+    [[ -z "$res" ]] || echo "    \"$target\"," >>"$file"
+done
+
+echo "];" >>"$file"

futures-channel/Cargo.toml

@@ -17,11 +17,10 @@ std = ["alloc", "futures-core/std"]
 alloc = ["futures-core/alloc"]
 sink = ["futures-sink"]
 
-# Unstable features
-# These features are outside of the normal semver guarantees and require the
-# `unstable` feature as an explicit opt-in to unstable API.
-unstable = ["futures-core/unstable"]
-cfg-target-has-atomic = ["futures-core/cfg-target-has-atomic"]
+# These features are no longer used.
+# TODO: remove in the next major version.
+unstable = []
+cfg-target-has-atomic = []
 
 [dependencies]
 futures-core = { path = "../futures-core", version = "0.3.14", default-features = false }

futures-channel/build.rs

@@ -0,0 +1,42 @@
+#![warn(rust_2018_idioms, single_use_lifetimes)]
+
+use std::env;
+
+include!("no_atomic_cas.rs");
+
+// The rustc-cfg listed below are considered public API, but it is *unstable*
+// and outside of the normal semver guarantees:
+//
+// - `futures_no_atomic_cas`
+//      Assume the target does not have atomic CAS (compare-and-swap).
+//      This is usually detected automatically by the build script, but you may
+//      need to enable it manually when building for custom targets or using
+//      non-cargo build systems that don't run the build script.
+//
+// With the exceptions mentioned above, the rustc-cfg strings below are
+// *not* public API. Please let us know by opening a GitHub issue if your build
+// environment requires some way to enable these cfgs other than by executing
+// our build script.
+fn main() {
+    let target = match env::var("TARGET") {
+        Ok(target) => target,
+        Err(e) => {
+            println!(
+                "cargo:warning={}: unable to get TARGET environment variable: {}",
+                env!("CARGO_PKG_NAME"),
+                e
+            );
+            return;
+        }
+    };
+
+    // Note that this is `no_*`, not `has_*`. This allows treating
+    // `cfg(target_has_atomic = "ptr")` as true when the build script doesn't
+    // run. This is needed for compatibility with non-cargo build systems that
+    // don't run the build script.
+    if NO_ATOMIC_CAS_TARGETS.contains(&&*target) {
+        println!("cargo:rustc-cfg=futures_no_atomic_cas");
+    }
+
+    println!("cargo:rerun-if-changed=no_atomic_cas.rs");
+}

futures-channel/no_atomic_cas.rs

@@ -0,0 +1 @@
+../no_atomic_cas.rs

futures-channel/src/lib.rs

@@ -11,20 +11,16 @@
 //! All items are only available when the `std` or `alloc` feature of this
 //! library is activated, and it is activated by default.
 
-#![cfg_attr(feature = "cfg-target-has-atomic", feature(cfg_target_has_atomic))]
 #![cfg_attr(not(feature = "std"), no_std)]
 #![warn(missing_docs, missing_debug_implementations, rust_2018_idioms, unreachable_pub)]
 // It cannot be included in the published code because this lints have false positives in the minimum required version.
 #![cfg_attr(test, warn(single_use_lifetimes))]
 #![warn(clippy::all)]
 #![doc(test(attr(deny(warnings), allow(dead_code, unused_assignments, unused_variables))))]
 
-#[cfg(all(feature = "cfg-target-has-atomic", not(feature = "unstable")))]
-compile_error!("The `cfg-target-has-atomic` feature requires the `unstable` feature as an explicit opt-in to unstable features");
-
 macro_rules! cfg_target_has_atomic {
     ($($item:item)*) => {$(
-        #[cfg_attr(feature = "cfg-target-has-atomic", cfg(target_has_atomic = "ptr"))]
+        #[cfg(not(futures_no_atomic_cas))]
         $item
     )*};
 }

futures-channel/src/lock.rs

@@ -6,8 +6,8 @@
 
 use core::cell::UnsafeCell;
 use core::ops::{Deref, DerefMut};
-use core::sync::atomic::Ordering::SeqCst;
 use core::sync::atomic::AtomicBool;
+use core::sync::atomic::Ordering::SeqCst;
 
 /// A "mutex" around a value, similar to `std::sync::Mutex<T>`.
 ///
@@ -37,10 +37,7 @@ unsafe impl<T: Send> Sync for Lock<T> {}
 impl<T> Lock<T> {
     /// Creates a new lock around the given value.
     pub(crate) fn new(t: T) -> Self {
-        Self {
-            locked: AtomicBool::new(false),
-            data: UnsafeCell::new(t),
-        }
+        Self { locked: AtomicBool::new(false), data: UnsafeCell::new(t) }
     }
 
     /// Attempts to acquire this lock, returning whether the lock was acquired or