Nix mangles TMPDIR path even when absolute on MacOSl

[jakubgs]

Describe the bug

I'm runnign 2.6.0 on MacOS and I'm seeing some strange behavior when setting TMPDIR.
Specifically, it appears Nix prefixes my absolute path with /private/, ignores slashes and creates an invalid path.

Steps To Reproduce

1. Crate simplest default.nix derivation:

echo '{ test = "TEST"; }' > default.nix

2. Make sure no TMPDIR is set

unset TMPDIR

4. Attempt to build the derivation. Without error this time.

nix-build --no-out-link

5. Set TMPDIR to some absolute path.

export TMPDIR=/tmp/test
mkdir -p $TMPDIR

6. Attempt to build the derivation.

nix-build --no-out-link

7. See error

error: getting status of '/private/tmptest': No such file or directory

Expected behavior

I'd expect Nix to use my TMPDIR as-is, without trying to modify it, but if it's trying to modify it to prefix it with /private it should at least do it correctly.

nix-env --version output

nix-env (Nix) 2.6.0

[jakubgs]

But as I typed it out I realized there is 2.6.1 which fixes this issue. And I think I even know which commit did it:

• 32a7724 - canonPath: fix missing slash when resolving links

So I mostly opened this just for documentation. In case anyone else encounters it.