Improve no_std handling

Stop using double negative cargo feature
This prevents accidently using items from std::prelude

https://www.reddit.com/r/rust/comments/1hs6spy/psa_for_std_feature_in_no_std_libraries

src/lib.rs

@@ -27,9 +27,12 @@
 #![warn(clippy::maybe_infinite_iter)]
 #![allow(clippy::uninlined_format_args)]
 #![allow(clippy::needless_lifetimes)]
-#![cfg_attr(not(any(feature = "std", test)), no_std)]
 #![cfg_attr(docsrs, feature(doc_cfg))]
 #![warn(missing_docs)]
+#![no_std]
+
+#[cfg(feature = "std")]
+extern crate std;
 
 extern crate alloc;
 

src/sparse_set/mod.rs

@@ -1029,6 +1029,7 @@ impl<T: 'static + Component> Storage for NonSendSync<SparseSet<T>> {
 mod tests {
     use super::*;
     use crate::Component;
+    use std::println;
 
     #[derive(PartialEq, Eq, Debug)]
     struct STR(&'static str);

src/sparse_set/sparse_array.rs

@@ -1,7 +1,5 @@
 use crate::entity_id::EntityId;
-#[cfg(not(feature = "std"))]
 use alloc::boxed::Box;
-#[cfg(not(feature = "std"))]
 use alloc::vec::Vec;
 use core::hint::unreachable_unchecked;
 use core::mem::size_of;

src/views/unique_or_default.rs

@@ -7,7 +7,8 @@ use crate::tracking::TrackingTimestamp;
 use crate::views::UniqueView;
 use crate::world::World;
 use crate::{error, BorrowInfo};
-use std::ops::Deref;
+use alloc::vec::Vec;
+use core::ops::Deref;
 
 /// Shared view over a unique component storage.
 ///

src/views/unique_or_default_mut.rs

@@ -7,7 +7,8 @@ use crate::tracking::TrackingTimestamp;
 use crate::views::UniqueViewMut;
 use crate::world::World;
 use crate::{error, BorrowInfo};
-use std::ops::{Deref, DerefMut};
+use alloc::vec::Vec;
+use core::ops::{Deref, DerefMut};
 
 /// Exclusive view over a unique component storage.
 ///

src/views/unique_or_init.rs

@@ -7,6 +7,7 @@ use crate::info::TypeInfo;
 use crate::tracking::TrackingTimestamp;
 use crate::views::UniqueView;
 use crate::world::World;
+use alloc::vec::Vec;
 use core::cell::OnceCell;
 
 /// Shared view over a unique component storage.

src/views/unique_or_init_mut.rs

@@ -7,6 +7,7 @@ use crate::info::TypeInfo;
 use crate::tracking::TrackingTimestamp;
 use crate::views::UniqueViewMut;
 use crate::world::World;
+use alloc::vec::Vec;
 use core::cell::OnceCell;
 
 /// Exclusive view over a unique component storage.

src/world/run_batches.rs

@@ -1,6 +1,7 @@
 use crate::error;
 use crate::scheduler::{Batches, Label};
 use crate::world::World;
+use alloc::boxed::Box;
 
 impl World {
     #[cfg(feature = "parallel")]
@@ -50,7 +51,7 @@ impl World {
                                 Ok(true)
                             }
                         })
-                        .collect::<Result<Vec<_>, error::RunWorkload>>()?,
+                        .collect::<Result<alloc::vec::Vec<_>, error::RunWorkload>>()?,
                 );
 
                 let mut start = 0;