Support creating asset directories (#16220)

# Objective

Exposes a means to create an asset directory (and its parent
directories). Wasn't sure whether we also wanted the variant to create
directories without the parent (i.e. `mkdir` instead of `mkdir -p`)?

Fixes bevyengine/bevy_editor_prototypes#144

Author: bas-ie

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

@@ -164,6 +164,12 @@ impl AssetWriter for FileAssetWriter {
         Ok(())
     }
 
+    async fn create_directory<'a>(&'a self, path: &'a Path) -> Result<(), AssetWriterError> {
+        let full_path = self.root_path.join(path);
+        async_fs::create_dir_all(full_path).await?;
+        Ok(())
+    }
+
     async fn remove_directory<'a>(&'a self, path: &'a Path) -> Result<(), AssetWriterError> {
         let full_path = self.root_path.join(path);
         async_fs::remove_dir_all(full_path).await?;

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

@@ -205,6 +205,12 @@ impl AssetWriter for FileAssetWriter {
         Ok(())
     }
 
+    async fn create_directory<'a>(&'a self, path: &'a Path) -> Result<(), AssetWriterError> {
+        let full_path = self.root_path.join(path);
+        std::fs::create_dir_all(full_path)?;
+        Ok(())
+    }
+
     async fn remove_directory<'a>(&'a self, path: &'a Path) -> Result<(), AssetWriterError> {
         let full_path = self.root_path.join(path);
         std::fs::remove_dir_all(full_path)?;

crates/bevy_asset/src/io/mod.rs

@@ -384,6 +384,12 @@ pub trait AssetWriter: Send + Sync + 'static {
         old_path: &'a Path,
         new_path: &'a Path,
     ) -> impl ConditionalSendFuture<Output = Result<(), AssetWriterError>>;
+    /// Creates a directory at the given path, including all parent directories if they do not
+    /// already exist.
+    fn create_directory<'a>(
+        &'a self,
+        path: &'a Path,
+    ) -> impl ConditionalSendFuture<Output = Result<(), AssetWriterError>>;
     /// Removes the directory at the given path, including all assets _and_ directories in that directory.
     fn remove_directory<'a>(
         &'a self,
@@ -460,6 +466,12 @@ pub trait ErasedAssetWriter: Send + Sync + 'static {
         old_path: &'a Path,
         new_path: &'a Path,
     ) -> BoxedFuture<'a, Result<(), AssetWriterError>>;
+    /// Creates a directory at the given path, including all parent directories if they do not
+    /// already exist.
+    fn create_directory<'a>(
+        &'a self,
+        path: &'a Path,
+    ) -> BoxedFuture<'a, Result<(), AssetWriterError>>;
     /// Removes the directory at the given path, including all assets _and_ directories in that directory.
     fn remove_directory<'a>(
         &'a self,
@@ -523,6 +535,12 @@ impl<T: AssetWriter> ErasedAssetWriter for T {
     ) -> BoxedFuture<'a, Result<(), AssetWriterError>> {
         Box::pin(Self::rename_meta(self, old_path, new_path))
     }
+    fn create_directory<'a>(
+        &'a self,
+        path: &'a Path,
+    ) -> BoxedFuture<'a, Result<(), AssetWriterError>> {
+        Box::pin(Self::create_directory(self, path))
+    }
     fn remove_directory<'a>(
         &'a self,
         path: &'a Path,