feature: Support for dereference links -L follow

du has -L flag which allows it to dereference or follow
symlinks. Clone this feature into dust.
https://github.com/bootandy/dust/issues/276

src/cli.rs

@@ -33,6 +33,12 @@ pub fn build_cli() -> Command<'static> {
                 .number_of_values(1)
                 .multiple_occurrences(true)
                 .help("Exclude any file or directory with this name"),
+        )
+         .arg(
+            Arg::new("dereference_links")
+                .short('L')
+                .long("dereference-links")
+                .help("dereference sym links - Treat sym links as directories and go into them"),
         )
         .arg(
             Arg::new("limit_filesystem")
@@ -136,6 +142,6 @@ pub fn build_cli() -> Command<'static> {
             Arg::new("only_dir")
                 .short('D')
                 .long("only-dir")
-                .help("Only directories will be displayed."), 
+                .help("Only directories will be displayed."),
         )
 }

src/dir_walker.rs

@@ -26,6 +26,7 @@ pub struct WalkData<'a> {
     pub use_apparent_size: bool,
     pub by_filecount: bool,
     pub ignore_hidden: bool,
+    pub follow_links: bool,
 }
 
 pub fn walk_it(dirs: HashSet<PathBuf>, walk_data: WalkData) -> (Vec<Node>, bool) {
@@ -144,7 +145,7 @@ fn walk(
 
                     if !ignore_file(entry, walk_data) {
                         if let Ok(data) = entry.file_type() {
-                            return if data.is_dir() && !data.is_symlink() {
+                            return if data.is_dir() || (walk_data.follow_links && data.is_symlink()) {
                                 walk(entry.path(), permissions_flag, walk_data, depth + 1)
                             } else {
                                 build_node(

src/main.rs

@@ -154,6 +154,7 @@ fn main() {
 
     let by_filecount = options.is_present("by_filecount");
     let limit_filesystem = options.is_present("limit_filesystem");
+    let follow_links = options.is_present("dereference_links");
 
     let simplified_dirs = simplify_dir_names(target_dirs);
     let allowed_filesystems = limit_filesystem
@@ -172,6 +173,7 @@ fn main() {
         use_apparent_size: config.get_apparent_size(&options),
         by_filecount,
         ignore_hidden: config.get_ignore_hidden(&options),
+        follow_links,
     };
     let _rayon = init_rayon();