Fix get_asset_paths not properly deleting empty folders (& recursive async functions) (#12638)

# Objective

get_asset_paths tries to check whether a folder is empty, and if so
delete it. However rather than checking whether any subfolder contains
files it checks whether _all_ subfolders have files.

Also cleanup various BoxedFutures in async recursive functions like
these, rust 1.77 now allows recursive async functions (albeit still by
boxing), hurray! This is a followup to #12550 (sorta). More BoxedFuture
stuff can be removed now that rust 1.77 is out, which can use async
recursive functions! This is mainly just cleaner code wise - the
recursion still boxes the future so not much to win there.

PR is mainly whitespace changes so do disable whitespace diffs for
easier review.

Cargo.toml

@@ -11,7 +11,7 @@ license = "MIT OR Apache-2.0"
 readme = "README.md"
 repository = "https://github.com/bevyengine/bevy"
 documentation = "https://docs.rs/bevy"
-rust-version = "1.76.0"
+rust-version = "1.77.0"
 
 [workspace]
 exclude = [

crates/bevy_asset/src/processor/mod.rs

@@ -20,7 +20,7 @@ use crate::{
 use bevy_ecs::prelude::*;
 use bevy_tasks::IoTaskPool;
 use bevy_utils::tracing::{debug, error, trace, warn};
-use bevy_utils::{BoxedFuture, HashMap, HashSet};
+use bevy_utils::{HashMap, HashSet};
 use futures_io::ErrorKind;
 use futures_lite::{AsyncReadExt, AsyncWriteExt, StreamExt};
 use parking_lot::RwLock;
@@ -435,27 +435,25 @@ impl AssetProcessor {
 
     #[allow(unused)]
     #[cfg(all(not(target_arch = "wasm32"), feature = "multi-threaded"))]
-    fn process_assets_internal<'scope>(
+    async fn process_assets_internal<'scope>(
         &'scope self,
         scope: &'scope bevy_tasks::Scope<'scope, '_, ()>,
         source: &'scope AssetSource,
         path: PathBuf,
-    ) -> BoxedFuture<'scope, Result<(), AssetReaderError>> {
-        Box::pin(async move {
-            if source.reader().is_directory(&path).await? {
-                let mut path_stream = source.reader().read_directory(&path).await?;
-                while let Some(path) = path_stream.next().await {
-                    self.process_assets_internal(scope, source, path).await?;
-                }
-            } else {
-                // Files without extensions are skipped
-                let processor = self.clone();
-                scope.spawn(async move {
-                    processor.process_asset(source, path).await;
-                });
+    ) -> Result<(), AssetReaderError> {
+        if source.reader().is_directory(&path).await? {
+            let mut path_stream = source.reader().read_directory(&path).await?;
+            while let Some(path) = path_stream.next().await {
+                Box::pin(self.process_assets_internal(scope, source, path)).await?;
             }
-            Ok(())
-        })
+        } else {
+            // Files without extensions are skipped
+            let processor = self.clone();
+            scope.spawn(async move {
+                processor.process_asset(source, path).await;
+            });
+        }
+        Ok(())
     }
 
     async fn try_reprocessing_queued(&self) {
@@ -514,34 +512,36 @@ impl AssetProcessor {
 
         /// Retrieves asset paths recursively. If `clean_empty_folders_writer` is Some, it will be used to clean up empty
         /// folders when they are discovered.
-        fn get_asset_paths<'a>(
+        async fn get_asset_paths<'a>(
             reader: &'a dyn ErasedAssetReader,
             clean_empty_folders_writer: Option<&'a dyn ErasedAssetWriter>,
             path: PathBuf,
             paths: &'a mut Vec<PathBuf>,
-        ) -> BoxedFuture<'a, Result<bool, AssetReaderError>> {
-            Box::pin(async move {
-                if reader.is_directory(&path).await? {
-                    let mut path_stream = reader.read_directory(&path).await?;
-                    let mut contains_files = false;
-                    while let Some(child_path) = path_stream.next().await {
-                        contains_files =
-                            get_asset_paths(reader, clean_empty_folders_writer, child_path, paths)
-                                .await?
-                                && contains_files;
-                    }
-                    if !contains_files && path.parent().is_some() {
-                        if let Some(writer) = clean_empty_folders_writer {
-                            // it is ok for this to fail as it is just a cleanup job.
-                            let _ = writer.remove_empty_directory(&path).await;
-                        }
-                    }
-                    Ok(contains_files)
-                } else {
-                    paths.push(path);
-                    Ok(true)
+        ) -> Result<bool, AssetReaderError> {
+            if reader.is_directory(&path).await? {
+                let mut path_stream = reader.read_directory(&path).await?;
+                let mut contains_files = false;
+
+                while let Some(child_path) = path_stream.next().await {
+                    contains_files |= Box::pin(get_asset_paths(
+                        reader,
+                        clean_empty_folders_writer,
+                        child_path,
+                        paths,
+                    ))
+                    .await?;
                 }
-            })
+                if !contains_files && path.parent().is_some() {
+                    if let Some(writer) = clean_empty_folders_writer {
+                        // it is ok for this to fail as it is just a cleanup job.
+                        let _ = writer.remove_empty_directory(&path).await;
+                    }
+                }
+                Ok(contains_files)
+            } else {
+                paths.push(path);
+                Ok(true)
+            }
         }
 
         for source in self.sources().iter_processed() {

crates/bevy_asset/src/server/mod.rs

@@ -658,38 +658,42 @@ impl AssetServer {
     }
 
     pub(crate) fn load_folder_internal(&self, id: UntypedAssetId, path: AssetPath) {
-        fn load_folder<'a>(
+        async fn load_folder<'a>(
             source: AssetSourceId<'static>,
             path: &'a Path,
             reader: &'a dyn ErasedAssetReader,
             server: &'a AssetServer,
             handles: &'a mut Vec<UntypedHandle>,
-        ) -> bevy_utils::BoxedFuture<'a, Result<(), AssetLoadError>> {
-            Box::pin(async move {
-                let is_dir = reader.is_directory(path).await?;
-                if is_dir {
-                    let mut path_stream = reader.read_directory(path.as_ref()).await?;
-                    while let Some(child_path) = path_stream.next().await {
-                        if reader.is_directory(&child_path).await? {
-                            load_folder(source.clone(), &child_path, reader, server, handles)
-                                .await?;
-                        } else {
-                            let path = child_path.to_str().expect("Path should be a valid string.");
-                            let asset_path = AssetPath::parse(path).with_source(source.clone());
-                            match server.load_untyped_async(asset_path).await {
-                                Ok(handle) => handles.push(handle),
-                                // skip assets that cannot be loaded
-                                Err(
-                                    AssetLoadError::MissingAssetLoaderForTypeName(_)
-                                    | AssetLoadError::MissingAssetLoaderForExtension(_),
-                                ) => {}
-                                Err(err) => return Err(err),
-                            }
+        ) -> Result<(), AssetLoadError> {
+            let is_dir = reader.is_directory(path).await?;
+            if is_dir {
+                let mut path_stream = reader.read_directory(path.as_ref()).await?;
+                while let Some(child_path) = path_stream.next().await {
+                    if reader.is_directory(&child_path).await? {
+                        Box::pin(load_folder(
+                            source.clone(),
+                            &child_path,
+                            reader,
+                            server,
+                            handles,
+                        ))
+                        .await?;
+                    } else {
+                        let path = child_path.to_str().expect("Path should be a valid string.");
+                        let asset_path = AssetPath::parse(path).with_source(source.clone());
+                        match server.load_untyped_async(asset_path).await {
+                            Ok(handle) => handles.push(handle),
+                            // skip assets that cannot be loaded
+                            Err(
+                                AssetLoadError::MissingAssetLoaderForTypeName(_)
+                                | AssetLoadError::MissingAssetLoaderForExtension(_),
+                            ) => {}
+                            Err(err) => return Err(err),
                         }
                     }
                 }
-                Ok(())
-            })
+            }
+            Ok(())
         }
 
         let path = path.into_owned();