isSymbolicLink or stat function returns wrong result

[Zoran Bošnjak]

isSymbolicLink or stat function does not work as expected. It returns False on actual symlink. However, isNotSymbolicLink function works as expected. Tested with turtle-1.5.16, using nix-shell on ubuntu-16.04. This is a simple test program:

{-# LANGUAGE OverloadedStrings #-}

module Main where

import           Prelude hiding (FilePath)
import           Turtle

-- | Create a file and a symlink, check symlink.
main :: IO ()
main = do
    let filename = "test.txt"
        linkname = "linkToFile"
    writeTextFile filename "some text"
    symlink filename linkname
    isSymbolicLink <$> stat linkname >>= print  -- Problem, expected True, got False.
    isNotSymbolicLink linkname >>= print        -- OK, got False as expected.

[Gabriella Gonzalez]

@zoranbosnjak: It's because stat follows symbolic links, whereas lstat does not follow symbolic links. See their respective documentation here:

• https://hackage.haskell.org/package/turtle-1.5.16/docs/Turtle-Prelude.html#v:stat
• https://hackage.haskell.org/package/turtle-1.5.16/docs/Turtle-Prelude.html#v:lstat

So the reason the first version returns False is because it's actually getting the FileStatus for the file that the symbolic link is pointing to and not the link itself.

[Zoran Bošnjak]

@Gabriel439: Thank you, I was not aware of lstat.

[Gabriella Gonzalez]

@zoranbosnjak: You're welcome! 🙂