Add a function to recursively list all entries in a directory with tokio.

src/command/build/mod.rs

@@ -1,5 +1,6 @@
 mod render;
 mod runner;
 mod stylesheet;
+mod walk_fs;
 
 pub(crate) use runner::build_site;

src/command/build/walk_fs.rs

@@ -0,0 +1,26 @@
+use std::ops::AsyncFn;
+use std::path::Path;
+
+use tokio::fs::DirEntry;
+
+use crate::error::CustomError;
+
+pub(crate) async fn walk_fs<P: AsRef<Path>, F: AsyncFn(&DirEntry) -> Result<bool, CustomError>>(
+    root: P,
+    predicate: F,
+) -> Result<Vec<DirEntry>, CustomError> {
+    let mut ret = Vec::new();
+    let mut entries = tokio::fs::read_dir(root).await?;
+    while let Some(entry) = entries.next_entry().await? {
+        let file_type = entry.file_type().await?;
+        if file_type.is_dir() {
+            let child_entries = walk_fs(entry.path(), &predicate).await?;
+            ret.extend(child_entries);
+        }
+        if predicate(&entry).await? {
+            ret.push(entry);
+        }
+    }
+
+    Ok(ret)
+}

src/main.rs

@@ -1,4 +1,5 @@
 #![feature(let_chains)]
+#![feature(async_closure)]
 use std::process::ExitCode;
 
 use clap::Parser;