allow feature = "std" when checking for presence of memory allocation

Memory allocation (i.e. the Box and Arc) can be present even without the
allocator_api.  Allow feature = "std" when the code is simply checking for
the existence of Box and Arc, and the allocator API is not used.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

examples/mutex.rs

@@ -162,12 +162,12 @@ impl WaitEntry {
     }
 }
 
-#[cfg(not(feature = "alloc"))]
+#[cfg(not(any(feature = "std", feature = "alloc")))]
 fn main() {}
 
 #[allow(dead_code)]
 #[cfg_attr(test, test)]
-#[cfg(feature = "alloc")]
+#[cfg(any(feature = "std", feature = "alloc"))]
 fn main() {
     let mtx: Pin<Arc<CMutex<usize>>> = Arc::pin_init(CMutex::new(0)).unwrap();
     let mut handles = vec![];

examples/pthread_mutex.rs

@@ -132,7 +132,7 @@ mod pthread_mtx {
 
 #[cfg_attr(test, test)]
 fn main() {
-    #[cfg(all(feature = "alloc", not(windows)))]
+    #[cfg(all(any(feature = "std", feature = "alloc"), not(windows)))]
     {
         use core::pin::Pin;
         use pinned_init::*;

examples/static_init.rs

@@ -77,10 +77,10 @@ unsafe impl PinInit<CMutex<usize>> for CountInit {
 
 pub static COUNT: StaticInit<CMutex<usize>, CountInit> = StaticInit::new(CountInit);
 
-#[cfg(not(feature = "alloc"))]
+#[cfg(not(any(feature = "std", feature = "alloc")))]
 fn main() {}
 
-#[cfg(feature = "alloc")]
+#[cfg(any(feature = "std", feature = "alloc"))]
 fn main() {
     let mtx: Pin<Arc<CMutex<usize>>> = Arc::pin_init(CMutex::new(0)).unwrap();
     let mut handles = vec![];

src/lib.rs

@@ -1274,7 +1274,7 @@ pub trait InPlaceWrite<T> {
     fn write_pin_init<E>(self, init: impl PinInit<T, E>) -> Result<Pin<Self::Initialized>, E>;
 }
 
-#[cfg(feature = "alloc")]
+#[cfg(any(feature = "std", feature = "alloc"))]
 impl<T> InPlaceWrite<T> for Box<MaybeUninit<T>> {
     type Initialized = Box<T>;
 
@@ -1405,7 +1405,7 @@ impl_zeroable! {
     //
     // In this case we are allowed to use `T: ?Sized`, since all zeros is the `None` variant.
     {<T: ?Sized>} Option<NonNull<T>>,
-    #[cfg(feature = "alloc")]
+    #[cfg(any(feature = "std", feature = "alloc"))]
     {<T: ?Sized>} Option<Box<T>>,
 
     // SAFETY: `null` pointer is valid.

tests/ring_buf.rs

@@ -192,7 +192,7 @@ fn even_stack() {
     assert_eq!(val, Err(()));
 }
 
-#[cfg(feature = "alloc")]
+#[cfg(any(feature = "std", feature = "alloc"))]
 #[test]
 fn even_failing() {
     assert!(matches!(Box::try_pin_init(EvenU64::new2(3)), Err(Error)));
@@ -243,7 +243,7 @@ struct BigStruct {
     oth: MaybeUninit<u8>,
 }
 
-#[cfg(all(feature = "alloc", not(miri)))]
+#[cfg(all(any(feature = "std", feature = "alloc"), not(miri)))]
 #[test]
 fn big_struct() {
     let x = Arc::init(init!(BigStruct {
@@ -258,7 +258,7 @@ fn big_struct() {
     println!("{x:?}");
 }
 
-#[cfg(all(feature = "alloc", not(miri)))]
+#[cfg(all(any(feature = "std", feature = "alloc"), not(miri)))]
 #[test]
 fn with_big_struct() {
     let buf = Arc::pin_init(CMutex::new(RingBuffer::<BigStruct, 64>::new())).unwrap();