make cd command complete only folders (#2431)

crates/nu-cli/src/shell/completer.rs

@@ -1,5 +1,6 @@
 use crate::completion::{self, Suggestion};
 use crate::context;
+use std::fs::metadata;
 
 pub(crate) struct NuCompleter {}
 
@@ -47,7 +48,12 @@ impl NuCompleter {
                         LocationType::Argument(_cmd, _arg_name) => {
                             // TODO use cmd and arg_name to narrow things down further
                             let path_completer = crate::completion::path::Completer::new();
-                            path_completer.complete(context, partial)
+                            let completed_paths = path_completer.complete(context, partial);
+                            if &line[..2] == "cd" {
+                                autocomplete_only_folders(completed_paths)
+                            } else {
+                                completed_paths
+                            }
                         }
 
                         LocationType::Variable => Vec::new(),
@@ -62,6 +68,18 @@ impl NuCompleter {
     }
 }
 
+fn autocomplete_only_folders(completed_paths: Vec<Suggestion>) -> Vec<Suggestion> {
+    let mut result = Vec::new();
+    for path in completed_paths {
+        let filepath = path.replacement.clone();
+        let md = metadata(filepath).expect("Expect filepath");
+        if md.is_dir() {
+            result.push(path);
+        }
+    }
+    result
+}
+
 fn requote(item: Suggestion) -> Suggestion {
     let unescaped = rustyline::completion::unescape(&item.replacement, Some('\\'));
     if unescaped != item.replacement {