builtins.toPath does not return a path

[veprbl]

Despite documentation saying

Convert the string value s into a path value. The string s must represent an
absolute path (i.e., must start with /).  The path need not exist. The
resulting path is canonicalised, e.g., builtins.toPath "//foo/xyzzy/../bar/"
returns /foo/bar.

I get

nix-repl> builtins.toPath "/tmp"
"/tmp"
nix-repl> builtins.typeOf (builtins.toPath "/tmp")
"string"

I see that this was already requested in #47 , but then later reverted in 17dc306 .

I see that most of the uses of toPath in nixpkgs employ a hack like

./. + builtins.toPath "/path/to/something"

which works.
I've also tried to re-revert the original patch and evaluate nixpkgs and the only thing that seems to be broken is texlive fails the evaluation

error: string `/nix/store/whrg59jzykznma6xjjajpckf4vq79cxj-texlive-cm-super-2015' cannot refer to other paths

This I don't know how to fix.
Also lib.isStorePath needs a simple fix to wrap the builtins.storeDir with builtins.toPath call.

[alexeymuranov]

Probably related:

builtins.toFile name s

Store the string s in a file in the Nix store and return its path. [...]

It would be the expected natural behaviour for me that it return a path object.

However, builtins.toFile actually returns the path as a string.

[domenkozar]

The gist of this issue:

nix-repl> :t ./. + "a"
a path

:t builtins.toPath "/a"
a string

:t builtins.toFile "foo" "a"
a string

Workaround is to use:

  toPath = s: ./. + s

[Warbo]

Here's an asPath function I've used as a workaround for absolute paths (those not starting at ./.). It takes the path ./., counts how many / it contains, appends that many /.. to the end, then appends the given path:

with builtins;
with lib;
with rec {
  herePath   = ./.;
  hereString = toString herePath;
  hereDepth  = length (filter (x: x == "/") (stringToCharacters hereString));
  upDots     = concatStringsSep "/" (map (_: "..") (range 1 hereDepth));
  rootPath   = ./. + "/${upDots}";

  stillNeeded  = typeOf (toPath herePath) == "string";
  obsoleteWarn = x:
    if stillNeeded
       then x
       else trace "WARNING: toPath makes paths, is asPath now redundant?" x;

  go = path: if typeOf path == "path"
                then path
                else rootPath + "${path}";
};

assert   typeOf rootPath == "path"       || abort "rootPath should be a path, got ${typeOf rootPath}";
assert toString rootPath == "/"          || abort "rootPath should be /, got ${toString rootPath}";
assert   typeOf (go ./.) == "path"       || abort "asPath of a path should produce a path, got ${typeOf (go ./.)}";
assert toString (go ./.) == toString ./. || abort "asPath result ${toString (go ./.)} didn't match input ${toString ./.}";
obsoleteWarn go

[veprbl]

@Warbo You can just write rootPath = /.;.

[veprbl]

Btw toPath is being phased out from nixpkgs in NixOS/nixpkgs#40937

[Warbo]

@veprbl Hah, never thought to check that! Thanks