Remove uses of unstable feature(cfg_target_has_atomic)

.github/workflows/ci.yml

@@ -23,8 +23,9 @@ jobs:
     name: test
     env:
       RUST_VERSION: ${{ matrix.rust }}
-      TARGET: ${{ matrix.target }}
+      RUST_TARGET: ${{ matrix.target }}
     strategy:
+      fail-fast: false
       matrix:
         include:
           - rust: 1.36.0
@@ -63,6 +64,7 @@ jobs:
     env:
       RUST_VERSION: ${{ matrix.rust }}
     strategy:
+      fail-fast: false
       matrix:
         rust:
           - 1.36.0
@@ -86,14 +88,27 @@ jobs:
       - name: dependency tree check
         run: ./ci/dependencies.sh
 
+  # When this job failed, run ci/no_atomic.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.sh
+      - run: git diff --exit-code
+
   # Check formatting.
   rustfmt:
     name: rustfmt
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
       - name: Install Rust
-        run: rustup update stable && rustup default stable
+        run: rustup update stable
       - name: rustfmt
         run: ./ci/rustfmt.sh
 
@@ -104,7 +119,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - name: Install Rust
-        run: rustup update stable && rustup default stable
+        run: rustup update stable
       - name: clippy
         run: ./ci/clippy.sh
 
@@ -126,7 +141,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - name: Install Rust
-        run: rustup update stable && rustup default stable
+        run: rustup update stable
       - name: loom
         run: ./ci/crossbeam-epoch-loom.sh
 
@@ -154,6 +169,7 @@ jobs:
       - test
       - features
       - dependencies
+      - codegen
       - rustfmt
       - clippy
       - san

Cargo.toml

@@ -36,8 +36,9 @@ alloc = ["crossbeam-epoch/alloc", "crossbeam-queue/alloc"]
 
 # Enable to use of unstable functionality.
 # This is disabled by default and requires recent nightly compiler.
-# Note that this is outside of the normal semver guarantees and minor versions
-# of crossbeam may make breaking changes to them at any time.
+#
+# NOTE: This feature is outside of the normal semver guarantees and minor or
+# patch versions of crossbeam may make breaking changes to them at any time.
 nightly = ["crossbeam-epoch/nightly", "crossbeam-utils/nightly", "crossbeam-queue/nightly"]
 
 [dependencies]

ci/check-features.sh

@@ -13,16 +13,19 @@ if [[ "$RUST_VERSION" != "nightly"* ]]; then
     # * `--no-dev-deps` - build without dev-dependencies to avoid https://github.com/rust-lang/cargo/issues/4866
     # * `--exclude benchmarks` - benchmarks doesn't published.
     # * `--skip nightly` - skip `nightly` feature as requires nightly compilers.
-    cargo hack check --all --feature-powerset --no-dev-deps --exclude benchmarks --skip nightly
+    cargo hack build --all --feature-powerset --no-dev-deps --exclude benchmarks --skip nightly
 else
     # On nightly, all feature　combinations should work.
-    cargo hack check --all --feature-powerset --no-dev-deps --exclude benchmarks
+    cargo hack build --all --feature-powerset --no-dev-deps --exclude benchmarks
 
-    # Check for no_std environment.
+    # Build for no_std environment.
+    # thumbv7m-none-eabi supports atomic CAS.
+    # thumbv6m-none-eabi supports atomic, but not atomic CAS.
+    # riscv32i-unknown-none-elf does not support atomic at all.
     rustup target add thumbv7m-none-eabi
     rustup target add thumbv6m-none-eabi
-    cargo hack check --all --feature-powerset --no-dev-deps --exclude benchmarks --target thumbv7m-none-eabi --skip std,default
-    # * `--features nightly` is required for enable `cfg_target_has_atomic`.
-    # * `--ignore-unknown-features` - some crates doesn't have 'nightly' feature
-    cargo hack check --all --feature-powerset --no-dev-deps --exclude benchmarks --target thumbv6m-none-eabi --skip std,default --features nightly --ignore-unknown-features
+    rustup target add riscv32i-unknown-none-elf
+    cargo hack build --all --feature-powerset --no-dev-deps --exclude benchmarks --target thumbv7m-none-eabi --skip std,default
+    cargo hack build --all --feature-powerset --no-dev-deps --exclude benchmarks --target thumbv6m-none-eabi --skip std,default
+    cargo hack build --all --feature-powerset --no-dev-deps --exclude benchmarks --target riscv32i-unknown-none-elf --skip std,default
 fi

ci/no_atomic.sh

@@ -0,0 +1,65 @@
+#!/bin/bash
+
+# Update the list of targets that do not support atomic/CAS operations.
+#
+# Usage:
+#    ./ci/no_atomic.sh
+
+set -euo pipefail
+IFS=$'\n\t'
+
+cd "$(cd "$(dirname "$0")" && pwd)"/..
+
+file="no_atomic.rs"
+
+{
+    echo "// This file is @generated by $(basename "$0")."
+    echo "// It is not intended for manual editing."
+    echo ""
+} >"$file"
+
+echo "const NO_ATOMIC_CAS: &[&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 "];" >>"$file"
+
+{
+    # Only crossbeam-utils actually uses this const.
+    echo "#[allow(dead_code)]"
+    echo "const NO_ATOMIC_64: &[&str] = &["
+} >>"$file"
+for target in $(rustc --print target-list); do
+    res=$(rustc --print target-spec-json -Z unstable-options --target "$target" \
+        | jq -r "select(.\"max-atomic-width\" == 32)")
+    [[ -z "$res" ]] || echo "    \"$target\"," >>"$file"
+done
+# It is not clear exactly what `"max-atomic-width" == null` means, but they
+# actually seem to have the same max-atomic-width as the target-pointer-width.
+# The targets currently included in this group are "mipsel-sony-psp",
+# "thumbv4t-none-eabi", "thumbv6m-none-eabi", all of which are
+# `"target-pointer-width" == "32"`, so assuming them `"max-atomic-width" == 32`
+# for now.
+for target in $(rustc --print target-list); do
+    res=$(rustc --print target-spec-json -Z unstable-options --target "$target" \
+        | jq -r "select(.\"max-atomic-width\" == null)")
+    [[ -z "$res" ]] || echo "    \"$target\"," >>"$file"
+done
+echo "];" >>"$file"
+
+# There is no `"max-atomic-width" == 16` or `"max-atomic-width" == 8` targets.
+
+# `"max-atomic-width" == 0` means that atomic is not supported at all.
+{
+    # Only crossbeam-utils actually uses this const.
+    echo "#[allow(dead_code)]"
+    echo "const NO_ATOMIC: &[&str] = &["
+} >>"$file"
+for target in $(rustc --print target-list); do
+    res=$(rustc --print target-spec-json -Z unstable-options --target "$target" \
+        | jq -r "select(.\"max-atomic-width\" == 0)")
+    [[ -z "$res" ]] || echo "    \"$target\"," >>"$file"
+done
+echo "];" >>"$file"

ci/test.sh

@@ -5,10 +5,10 @@ set -ex
 
 export RUSTFLAGS="-D warnings"
 
-if [[ -n "$TARGET" ]]; then
-    # If TARGET is specified, use cross for testing.
+if [[ -n "$RUST_TARGET" ]]; then
+    # If RUST_TARGET is specified, use cross for testing.
     cargo install cross
-    cross test --all --target "$TARGET" --exclude benchmarks -- --test-threads=1
+    cross test --all --target "$RUST_TARGET" --exclude benchmarks -- --test-threads=1
 
     # For now, the non-host target only runs tests.
     exit 0

crossbeam-channel/Cargo.toml

@@ -20,6 +20,8 @@ default = ["std"]
 
 # Enable to use APIs that require `std`.
 # This is enabled by default.
+#
+# NOTE: Disabling `std` feature is not supported yet.
 std = ["crossbeam-utils/std"]
 
 [dependencies]

crossbeam-deque/Cargo.toml

@@ -20,6 +20,8 @@ default = ["std"]
 
 # Enable to use APIs that require `std`.
 # This is enabled by default.
+#
+# NOTE: Disabling `std` feature is not supported yet.
 std = ["crossbeam-epoch/std", "crossbeam-utils/std"]
 
 [dependencies]

crossbeam-epoch/Cargo.toml

@@ -24,18 +24,21 @@ std = ["alloc", "crossbeam-utils/std", "lazy_static"]
 
 # Enable to use APIs that require `alloc`.
 # This is enabled by default and also enabled if the `std` feature is enabled.
+#
+# NOTE: Disabling both `std` *and* `alloc` features is not supported yet.
 alloc = []
 
 # Enable to use of unstable functionality.
 # This is disabled by default and requires recent nightly compiler.
-# Note that this is outside of the normal semver guarantees and minor versions
-# of crossbeam may make breaking changes to them at any time.
+#
+# NOTE: This feature is outside of the normal semver guarantees and minor or
+# patch versions of crossbeam may make breaking changes to them at any time.
 nightly = ["crossbeam-utils/nightly", "const_fn"]
 
 # Enable the use of loom for concurrency testing.
 #
-# This configuration option is outside of the normal semver guarantees: minor
-# versions of crossbeam may make breaking changes to it at any time.
+# NOTE: This feature is outside of the normal semver guarantees and minor or
+# patch versions of crossbeam may make breaking changes to them at any time.
 loom = ["loom-crate", "crossbeam-utils/loom"]
 
 [dependencies]
@@ -45,8 +48,8 @@ memoffset = "0.6"
 
 # Enable the use of loom for concurrency testing.
 #
-# This configuration option is outside of the normal semver guarantees: minor
-# versions of crossbeam may make breaking changes to it at any time.
+# NOTE: This feature is outside of the normal semver guarantees and minor or
+# patch versions of crossbeam may make breaking changes to them at any time.
 [target.'cfg(crossbeam_loom)'.dependencies]
 loom-crate = { package = "loom", version = "0.5", optional = true }
 

crossbeam-epoch/build.rs

@@ -0,0 +1,32 @@
+#![warn(rust_2018_idioms)]
+
+use std::env;
+
+include!("no_atomic.rs");
+
+// 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.contains(&&*target) {
+        println!("cargo:rustc-cfg=crossbeam_no_atomic_cas");
+    }
+
+    println!("cargo:rerun-if-changed=no_atomic.rs");
+}

crossbeam-epoch/no_atomic.rs

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

crossbeam-epoch/src/lib.rs

@@ -62,7 +62,6 @@
     unreachable_pub
 )]
 #![cfg_attr(not(feature = "std"), no_std)]
-#![cfg_attr(feature = "nightly", feature(cfg_target_has_atomic))]
 #![cfg_attr(feature = "nightly", feature(const_fn_trait_bound))]
 
 #[cfg(crossbeam_loom)]
@@ -105,10 +104,11 @@ mod primitive {
     pub(crate) use loom::lazy_static;
     pub(crate) use loom::thread_local;
 }
+#[cfg(not(crossbeam_no_atomic_cas))]
 #[cfg(not(crossbeam_loom))]
 #[allow(unused_imports, dead_code)]
 mod primitive {
-    #[cfg(any(feature = "alloc", feature = "std"))]
+    #[cfg(feature = "alloc")]
     pub(crate) mod cell {
         #[derive(Debug)]
         #[repr(transparent)]
@@ -136,14 +136,13 @@ mod primitive {
             }
         }
     }
-    #[cfg(any(feature = "alloc", feature = "std"))]
+    #[cfg(feature = "alloc")]
     pub(crate) mod sync {
         pub(crate) mod atomic {
             pub(crate) use core::sync::atomic::compiler_fence;
             pub(crate) use core::sync::atomic::fence;
             pub(crate) use core::sync::atomic::AtomicUsize;
         }
-        #[cfg_attr(feature = "nightly", cfg(target_has_atomic = "ptr"))]
         pub(crate) use alloc::sync::Arc;
     }
 
@@ -154,7 +153,7 @@ mod primitive {
     pub(crate) use lazy_static::lazy_static;
 }
 
-#[cfg_attr(feature = "nightly", cfg(target_has_atomic = "ptr"))]
+#[cfg(not(crossbeam_no_atomic_cas))]
 cfg_if! {
     if #[cfg(feature = "alloc")] {
         extern crate alloc;

crossbeam-queue/Cargo.toml

@@ -24,12 +24,17 @@ std = ["alloc", "crossbeam-utils/std"]
 
 # Enable to use APIs that require `alloc`.
 # This is enabled by default and also enabled if the `std` feature is enabled.
+#
+# NOTE: Disabling both `std` *and* `alloc` features is not supported yet.
 alloc = []
 
+# These features are no longer used.
+# TODO: remove in the next major version.
 # Enable to use of unstable functionality.
 # This is disabled by default and requires recent nightly compiler.
-# Note that this is outside of the normal semver guarantees and minor versions
-# of crossbeam may make breaking changes to them at any time.
+#
+# NOTE: This feature is outside of the normal semver guarantees and minor or
+# patch versions of crossbeam may make breaking changes to them at any time.
 nightly = ["crossbeam-utils/nightly"]
 
 [dependencies]

crossbeam-queue/build.rs

@@ -0,0 +1,32 @@
+#![warn(rust_2018_idioms)]
+
+use std::env;
+
+include!("no_atomic.rs");
+
+// 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.contains(&&*target) {
+        println!("cargo:rustc-cfg=crossbeam_no_atomic_cas");
+    }
+
+    println!("cargo:rerun-if-changed=no_atomic.rs");
+}

crossbeam-queue/no_atomic.rs

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

crossbeam-queue/src/lib.rs

@@ -19,9 +19,8 @@
     unreachable_pub
 )]
 #![cfg_attr(not(feature = "std"), no_std)]
-#![cfg_attr(feature = "nightly", feature(cfg_target_has_atomic))]
 
-#[cfg_attr(feature = "nightly", cfg(target_has_atomic = "ptr"))]
+#[cfg(not(crossbeam_no_atomic_cas))]
 cfg_if::cfg_if! {
     if #[cfg(feature = "alloc")] {
         extern crate alloc;