lib.filesystem.pathType: Fix for filesystem root argument

Previously this function couldn't handle / being passed, it would throw
an error:

error: attribute '' missing

       at nixpkgs/lib/filesystem.nix:24:20:

           23|   */
           24|   pathType = path: (readDir (dirOf path)).${baseNameOf path};
             |                    ^
           25|

Consequently this also fixes the
lib.filesystem.{pathIsDirectory,pathIsRegularFile} functions.

1 files changed, 6 insertions, 1 deletions

diff --git a/lib/filesystem.nix b/lib/filesystem.nix
index f604eb90434b1..13f4ebb26402f 100644
--- a/lib/filesystem.nix
+++ b/lib/filesystem.nix
@@ -22,7 +22,12 @@ in
     Returns the type of a path: regular (for file), symlink, or directory.
   */
   pathType = path:
-    (readDir (dirOf path)).${baseNameOf path};
+    # The filesystem root is the only path where `dirOf / == /` and
+    # `baseNameOf /` is not valid. We can detect this and directly return
+    # "directory", since we know the filesystem root can't be anything else.
+    if dirOf path == path
+    then "directory"
+    else (readDir (dirOf path)).${baseNameOf path};
 
   /*
     Returns true if the path exists and is a directory, false otherwise.