Switch bevy_asset to core::prelude (#17442)

Makes use of `std` explicit, simplifying a possible `no_std` port.

# Objective

- Contributes to #15460
- Simplify future `no_std` work on `bevy_asset`

## Solution

- Add `#![no_std]` to switch to `core::prelude` instead of
`std::prelude`

## Testing

- CI

---

## Notes

This is entirely a change around the names of imports and has no impact
on functionality. This just reduces the quantity of changes involved in
the (likely more controversial) `no_std`-ification of `bevy_asset`.

Author: bushrat011899

crates/bevy_asset/src/asset_changed.rs

@@ -288,7 +288,9 @@ unsafe impl<A: AsAssetId> QueryFilter for AssetChanged<A> {
 #[cfg(test)]
 mod tests {
     use crate::{self as bevy_asset, AssetEvents, AssetPlugin, Handle};
+    use alloc::{vec, vec::Vec};
     use core::num::NonZero;
+    use std::println;
 
     use crate::{AssetApp, Assets};
     use bevy_app::{App, AppExit, Last, Startup, TaskPoolPlugin, Update};

crates/bevy_asset/src/assets.rs

@@ -3,7 +3,7 @@ use crate::{
     self as bevy_asset, Asset, AssetEvent, AssetHandleProvider, AssetId, AssetServer, Handle,
     UntypedHandle,
 };
-use alloc::sync::Arc;
+use alloc::{sync::Arc, vec::Vec};
 use bevy_ecs::{
     prelude::EventWriter,
     system::{Res, ResMut, Resource, SystemChangeTick},

crates/bevy_asset/src/folder.rs

@@ -1,3 +1,5 @@
+use alloc::vec::Vec;
+
 use crate as bevy_asset;
 use crate::{Asset, UntypedHandle};
 use bevy_reflect::TypePath;

crates/bevy_asset/src/handle.rs

@@ -514,6 +514,7 @@ pub enum UntypedAssetConversionError {
 
 #[cfg(test)]
 mod tests {
+    use alloc::boxed::Box;
     use bevy_reflect::PartialReflect;
     use bevy_utils::FixedHasher;
     use core::hash::BuildHasher;

crates/bevy_asset/src/io/android.rs

@@ -1,7 +1,7 @@
 use crate::io::{get_meta_path, AssetReader, AssetReaderError, PathStream, Reader, VecReader};
+use alloc::{borrow::ToOwned, boxed::Box, ffi::CString, vec::Vec};
 use futures_lite::stream;
-use std::{ffi::CString, path::Path};
-use tracing::error;
+use std::path::Path;
 
 /// [`AssetReader`] implementation for Android devices, built on top of Android's [`AssetManager`].
 ///
@@ -72,10 +72,7 @@ impl AssetReader for AndroidAssetReader {
         Ok(read_dir)
     }
 
-    async fn is_directory<'a>(
-        &'a self,
-        path: &'a Path,
-    ) -> std::result::Result<bool, AssetReaderError> {
+    async fn is_directory<'a>(&'a self, path: &'a Path) -> Result<bool, AssetReaderError> {
         let asset_manager = bevy_window::ANDROID_APP
             .get()
             .expect("Bevy must be setup with the #[bevy_main] macro on Android")

crates/bevy_asset/src/io/embedded/embedded_watcher.rs

@@ -3,7 +3,7 @@ use crate::io::{
     memory::Dir,
     AssetSourceEvent, AssetWatcher,
 };
-use alloc::sync::Arc;
+use alloc::{boxed::Box, sync::Arc, vec::Vec};
 use bevy_utils::HashMap;
 use core::time::Duration;
 use notify_debouncer_full::{notify::RecommendedWatcher, Debouncer, RecommendedCache};

crates/bevy_asset/src/io/embedded/mod.rs

@@ -8,9 +8,13 @@ use crate::io::{
     memory::{Dir, MemoryAssetReader, Value},
     AssetSource, AssetSourceBuilders,
 };
+use alloc::boxed::Box;
 use bevy_ecs::system::Resource;
 use std::path::{Path, PathBuf};
 
+#[cfg(feature = "embedded_watcher")]
+use alloc::borrow::ToOwned;
+
 pub const EMBEDDED: &str = "embedded";
 
 /// A [`Resource`] that manages "rust source files" in a virtual in memory [`Dir`], which is intended
@@ -29,7 +33,7 @@ impl EmbeddedAssetRegistry {
     /// Inserts a new asset. `full_path` is the full path (as [`file`] would return for that file, if it was capable of
     /// running in a non-rust file). `asset_path` is the path that will be used to identify the asset in the `embedded`
     /// [`AssetSource`]. `value` is the bytes that will be returned for the asset. This can be _either_ a `&'static [u8]`
-    /// or a [`Vec<u8>`].
+    /// or a [`Vec<u8>`](alloc::vec::Vec).
     #[cfg_attr(
         not(feature = "embedded_watcher"),
         expect(
@@ -48,7 +52,7 @@ impl EmbeddedAssetRegistry {
     /// Inserts new asset metadata. `full_path` is the full path (as [`file`] would return for that file, if it was capable of
     /// running in a non-rust file). `asset_path` is the path that will be used to identify the asset in the `embedded`
     /// [`AssetSource`]. `value` is the bytes that will be returned for the asset. This can be _either_ a `&'static [u8]`
-    /// or a [`Vec<u8>`].
+    /// or a [`Vec<u8>`](alloc::vec::Vec).
     #[cfg_attr(
         not(feature = "embedded_watcher"),
         expect(

crates/bevy_asset/src/io/file/file_asset.rs

@@ -6,6 +6,7 @@ use async_fs::{read_dir, File};
 use futures_io::AsyncSeek;
 use futures_lite::StreamExt;
 
+use alloc::{borrow::ToOwned, boxed::Box};
 use core::{pin::Pin, task, task::Poll};
 use std::path::Path;
 

crates/bevy_asset/src/io/file/file_watcher.rs

@@ -2,6 +2,7 @@ use crate::{
     io::{AssetSourceEvent, AssetWatcher},
     path::normalize_path,
 };
+use alloc::borrow::ToOwned;
 use core::time::Duration;
 use crossbeam_channel::Sender;
 use notify_debouncer_full::{

crates/bevy_asset/src/io/file/mod.rs

@@ -10,6 +10,7 @@ mod sync_file_asset;
 pub use file_watcher::*;
 use tracing::{debug, error};
 
+use alloc::borrow::ToOwned;
 use std::{
     env,
     path::{Path, PathBuf},