Remove uses of autocfg

Detect platforms that do not support AtomicU64 by using the same way.
AFAIK, this is more robust than the current way that uses autocfg.
See also rust-lang/futures-rs#2294.

Author: taiki-e

ci/no_atomic.sh

@@ -26,6 +26,31 @@ for target in $(rustc --print target-list); do
 done
 echo "];" >>"$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.

crossbeam-utils/Cargo.toml

@@ -42,8 +42,5 @@ lazy_static = { version = "1.4.0", optional = true }
 [target.'cfg(crossbeam_loom)'.dependencies]
 loom = { version = "0.5", optional = true }
 
-[build-dependencies]
-autocfg = "1.0.0"
-
 [dev-dependencies]
 rand = "0.8"

crossbeam-utils/build.rs

@@ -2,8 +2,6 @@
 
 use std::env;
 
-use autocfg::AutoCfg;
-
 include!("no_atomic.rs");
 
 // The rustc-cfg strings below are *not* public API. Please let us know by
@@ -31,25 +29,12 @@ fn main() {
     }
     if NO_ATOMIC.contains(&&*target) {
         println!("cargo:rustc-cfg=crossbeam_no_atomic");
+        println!("cargo:rustc-cfg=crossbeam_no_atomic_64");
+    } else if NO_ATOMIC_64.contains(&&*target) {
+        println!("cargo:rustc-cfg=crossbeam_no_atomic_64");
+    } else {
+        // Otherwise, assuming `"max-atomic-width" == 64`.
     }
 
-    let cfg = match AutoCfg::new() {
-        Ok(cfg) => cfg,
-        Err(e) => {
-            println!(
-                "cargo:warning={}: unable to determine rustc version: {}",
-                env!("CARGO_PKG_NAME"),
-                e
-            );
-            return;
-        }
-    };
-
-    cfg.emit_type_cfg("core::sync::atomic::AtomicU8", "has_atomic_u8");
-    cfg.emit_type_cfg("core::sync::atomic::AtomicU16", "has_atomic_u16");
-    cfg.emit_type_cfg("core::sync::atomic::AtomicU32", "has_atomic_u32");
-    cfg.emit_type_cfg("core::sync::atomic::AtomicU64", "has_atomic_u64");
-    cfg.emit_type_cfg("core::sync::atomic::AtomicU128", "has_atomic_u128");
-
     println!("cargo:rerun-if-changed=no_atomic.rs");
 }

crossbeam-utils/src/atomic/atomic_cell.rs

@@ -497,26 +497,19 @@ macro_rules! impl_arithmetic {
     };
 }
 
-#[cfg(has_atomic_u8)]
 impl_arithmetic!(u8, atomic::AtomicU8, "let a = AtomicCell::new(7u8);");
-#[cfg(all(has_atomic_u8, not(crossbeam_loom)))]
 impl_arithmetic!(i8, atomic::AtomicI8, "let a = AtomicCell::new(7i8);");
-#[cfg(has_atomic_u16)]
 impl_arithmetic!(u16, atomic::AtomicU16, "let a = AtomicCell::new(7u16);");
-#[cfg(all(has_atomic_u16, not(crossbeam_loom)))]
 impl_arithmetic!(i16, atomic::AtomicI16, "let a = AtomicCell::new(7i16);");
-#[cfg(has_atomic_u32)]
 impl_arithmetic!(u32, atomic::AtomicU32, "let a = AtomicCell::new(7u32);");
-#[cfg(all(has_atomic_u32, not(crossbeam_loom)))]
 impl_arithmetic!(i32, atomic::AtomicI32, "let a = AtomicCell::new(7i32);");
-#[cfg(has_atomic_u64)]
+#[cfg(not(crossbeam_no_atomic_64))]
 impl_arithmetic!(u64, atomic::AtomicU64, "let a = AtomicCell::new(7u64);");
-#[cfg(all(has_atomic_u64, not(crossbeam_loom)))]
+#[cfg(not(crossbeam_no_atomic_64))]
 impl_arithmetic!(i64, atomic::AtomicI64, "let a = AtomicCell::new(7i64);");
-#[cfg(all(has_atomic_u128, not(crossbeam_loom)))]
-impl_arithmetic!(u128, atomic::AtomicU128, "let a = AtomicCell::new(7u128);");
-#[cfg(all(has_atomic_u128, not(crossbeam_loom)))]
-impl_arithmetic!(i128, atomic::AtomicI128, "let  a = AtomicCell::new(7i128);");
+// TODO: AtomicU128 is unstable
+// impl_arithmetic!(u128, atomic::AtomicU128, "let a = AtomicCell::new(7u128);");
+// impl_arithmetic!(i128, atomic::AtomicI128, "let a = AtomicCell::new(7i128);");
 
 impl_arithmetic!(
     usize,
@@ -809,16 +802,13 @@ macro_rules! atomic {
             atomic!(@check, $t, AtomicUnit, $a, $atomic_op);
             atomic!(@check, $t, atomic::AtomicUsize, $a, $atomic_op);
 
-            #[cfg(has_atomic_u8)]
             atomic!(@check, $t, atomic::AtomicU8, $a, $atomic_op);
-            #[cfg(has_atomic_u16)]
             atomic!(@check, $t, atomic::AtomicU16, $a, $atomic_op);
-            #[cfg(has_atomic_u32)]
             atomic!(@check, $t, atomic::AtomicU32, $a, $atomic_op);
-            #[cfg(has_atomic_u64)]
+            #[cfg(not(crossbeam_no_atomic_64))]
             atomic!(@check, $t, atomic::AtomicU64, $a, $atomic_op);
-            #[cfg(has_atomic_u128)]
-            atomic!(@check, $t, atomic::AtomicU128, $a, $atomic_op);
+            // TODO: AtomicU128 is unstable
+            // atomic!(@check, $t, atomic::AtomicU128, $a, $atomic_op);
 
             #[cfg(crossbeam_loom)]
             unimplemented!("loom does not support non-atomic atomic ops");
@@ -831,17 +821,15 @@ macro_rules! atomic {
 /// Returns `true` if operations on `AtomicCell<T>` are lock-free.
 const fn atomic_is_lock_free<T>() -> bool {
     // HACK(taiki-e): This is equivalent to `atomic! { T, _a, true, false }`, but can be used in const fn even in Rust 1.36.
-    let is_lock_free = can_transmute::<T, AtomicUnit>() | can_transmute::<T, atomic::AtomicUsize>();
-    #[cfg(has_atomic_u8)]
-    let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU8>();
-    #[cfg(has_atomic_u16)]
-    let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU16>();
-    #[cfg(has_atomic_u32)]
-    let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU32>();
-    #[cfg(has_atomic_u64)]
+    let is_lock_free = can_transmute::<T, AtomicUnit>()
+        | can_transmute::<T, atomic::AtomicUsize>()
+        | can_transmute::<T, atomic::AtomicU8>()
+        | can_transmute::<T, atomic::AtomicU16>()
+        | can_transmute::<T, atomic::AtomicU32>();
+    #[cfg(not(crossbeam_no_atomic_64))]
     let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU64>();
-    #[cfg(has_atomic_u128)]
-    let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU128>();
+    // TODO: AtomicU128 is unstable
+    // let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU128>();
     is_lock_free
 }
 

crossbeam-utils/src/atomic/consume.rs

@@ -68,21 +68,15 @@ macro_rules! impl_atomic {
 impl_atomic!(AtomicBool, bool);
 impl_atomic!(AtomicUsize, usize);
 impl_atomic!(AtomicIsize, isize);
-#[cfg(has_atomic_u8)]
 impl_atomic!(AtomicU8, u8);
-#[cfg(has_atomic_u8)]
 impl_atomic!(AtomicI8, i8);
-#[cfg(has_atomic_u16)]
 impl_atomic!(AtomicU16, u16);
-#[cfg(has_atomic_u16)]
 impl_atomic!(AtomicI16, i16);
-#[cfg(has_atomic_u32)]
 impl_atomic!(AtomicU32, u32);
-#[cfg(has_atomic_u32)]
 impl_atomic!(AtomicI32, i32);
-#[cfg(has_atomic_u64)]
+#[cfg(not(crossbeam_no_atomic_64))]
 impl_atomic!(AtomicU64, u64);
-#[cfg(has_atomic_u64)]
+#[cfg(not(crossbeam_no_atomic_64))]
 impl_atomic!(AtomicI64, i64);
 
 #[cfg(not(crossbeam_no_atomic))]

crossbeam-utils/src/lib.rs

@@ -72,16 +72,12 @@ mod primitive {
             #[cfg(not(crossbeam_no_atomic))]
             pub(crate) use core::sync::atomic::{AtomicBool, AtomicIsize, AtomicUsize};
             #[cfg(not(crossbeam_no_atomic))]
-            #[cfg(has_atomic_u16)]
             pub(crate) use core::sync::atomic::{AtomicI16, AtomicU16};
             #[cfg(not(crossbeam_no_atomic))]
-            #[cfg(has_atomic_u32)]
             pub(crate) use core::sync::atomic::{AtomicI32, AtomicU32};
-            #[cfg(not(crossbeam_no_atomic))]
-            #[cfg(has_atomic_u64)]
+            #[cfg(not(crossbeam_no_atomic_64))]
             pub(crate) use core::sync::atomic::{AtomicI64, AtomicU64};
             #[cfg(not(crossbeam_no_atomic))]
-            #[cfg(has_atomic_u8)]
             pub(crate) use core::sync::atomic::{AtomicI8, AtomicU8};
         }
 

crossbeam-utils/tests/atomic_cell.rs

@@ -9,17 +9,23 @@ fn is_lock_free() {
     struct U8Wrap(bool);
     struct I16Wrap(i16);
 
-    assert_eq!(AtomicCell::<usize>::is_lock_free(), true);
-    assert_eq!(AtomicCell::<isize>::is_lock_free(), true);
-    assert_eq!(AtomicCell::<UsizeWrap>::is_lock_free(), true);
+    assert!(AtomicCell::<usize>::is_lock_free());
+    assert!(AtomicCell::<isize>::is_lock_free());
+    assert!(AtomicCell::<UsizeWrap>::is_lock_free());
 
-    assert_eq!(AtomicCell::<u8>::is_lock_free(), cfg!(has_atomic_u8));
-    assert_eq!(AtomicCell::<bool>::is_lock_free(), cfg!(has_atomic_u8));
-    assert_eq!(AtomicCell::<U8Wrap>::is_lock_free(), cfg!(has_atomic_u8));
+    assert!(AtomicCell::<u8>::is_lock_free());
+    assert!(AtomicCell::<bool>::is_lock_free());
+    assert!(AtomicCell::<U8Wrap>::is_lock_free());
 
-    assert_eq!(AtomicCell::<I16Wrap>::is_lock_free(), cfg!(has_atomic_u16));
+    assert!(AtomicCell::<I16Wrap>::is_lock_free());
 
-    assert_eq!(AtomicCell::<u128>::is_lock_free(), cfg!(has_atomic_u128));
+    assert_eq!(
+        AtomicCell::<u64>::is_lock_free(),
+        cfg!(not(crossbeam_no_atomic_64))
+    );
+
+    // AtomicU128 is unstable
+    assert!(!AtomicCell::<u128>::is_lock_free());
 }
 
 #[test]

no_atomic.rs

@@ -10,6 +10,47 @@ const NO_ATOMIC_CAS: &[&str] = &[
     "thumbv6m-none-eabi",
 ];
 #[allow(dead_code)]
+const NO_ATOMIC_64: &[&str] = &[
+    "arm-linux-androideabi",
+    "armebv7r-none-eabi",
+    "armebv7r-none-eabihf",
+    "armv4t-unknown-linux-gnueabi",
+    "armv5te-unknown-linux-gnueabi",
+    "armv5te-unknown-linux-musleabi",
+    "armv5te-unknown-linux-uclibceabi",
+    "armv7r-none-eabi",
+    "armv7r-none-eabihf",
+    "hexagon-unknown-linux-musl",
+    "mips-unknown-linux-gnu",
+    "mips-unknown-linux-musl",
+    "mips-unknown-linux-uclibc",
+    "mipsel-unknown-linux-gnu",
+    "mipsel-unknown-linux-musl",
+    "mipsel-unknown-linux-uclibc",
+    "mipsel-unknown-none",
+    "mipsisa32r6-unknown-linux-gnu",
+    "mipsisa32r6el-unknown-linux-gnu",
+    "powerpc-unknown-linux-gnu",
+    "powerpc-unknown-linux-gnuspe",
+    "powerpc-unknown-linux-musl",
+    "powerpc-unknown-netbsd",
+    "powerpc-unknown-openbsd",
+    "powerpc-wrs-vxworks",
+    "powerpc-wrs-vxworks-spe",
+    "riscv32gc-unknown-linux-gnu",
+    "riscv32gc-unknown-linux-musl",
+    "riscv32imac-unknown-none-elf",
+    "thumbv7em-none-eabi",
+    "thumbv7em-none-eabihf",
+    "thumbv7m-none-eabi",
+    "thumbv8m.base-none-eabi",
+    "thumbv8m.main-none-eabi",
+    "thumbv8m.main-none-eabihf",
+    "mipsel-sony-psp",
+    "thumbv4t-none-eabi",
+    "thumbv6m-none-eabi",
+];
+#[allow(dead_code)]
 const NO_ATOMIC: &[&str] = &[
     "avr-unknown-gnu-atmega328",
     "msp430-none-elf",