Feature: Re-introduce -x flag to limit filesystem

-x flag allows dust to limit itself to the current filesystem

src/utils.rs

@@ -1,6 +1,9 @@
+use platform::get_metadata;
 use std::collections::HashSet;
 use std::path::{Path, PathBuf};
 
+use crate::platform;
+
 fn is_a_parent_of<P: AsRef<Path>>(parent: P, child: P) -> bool {
     let parent = parent.as_ref();
     let child = child.as_ref();
@@ -33,6 +36,22 @@ pub fn simplify_dir_names<P: AsRef<Path>>(filenames: Vec<P>) -> HashSet<PathBuf>
     top_level_names
 }
 
+pub fn get_filesystem_devices<'a, P: IntoIterator<Item = &'a PathBuf>>(paths: P) -> HashSet<u64> {
+    // Gets the device ids for the filesystems which are used by the argument paths
+    paths
+        .into_iter()
+        .filter_map(|p| {
+            let meta = get_metadata(&p, false);
+
+            if let Some((_size, Some((_id, dev)))) = meta {
+                Some(dev)
+            } else {
+                None
+            }
+        })
+        .collect()
+}
+
 pub fn normalize_path<P: AsRef<Path>>(path: P) -> PathBuf {
     // normalize path ...
     // 1. removing repeated separators