Add tests/functional/lang/eval-fail-readDir-storeDir-pure

[roberth]

Motivation

Add missing test case.

• It's the wrong error. Make --pure-eval --expr without flakes work. Reproducable outside the test framework. Not sensitive to NIX_PATH environment variable or --nix-path "".

$ nix-instantiate --pure-eval tests/functional/lang/eval-fail-readDir-storeDir-pure.nix
error: access to absolute path '/home' is forbidden in pure evaluation mode (use '--impure' to override)

Context

• pathExists: Return false on "/nix/store" in pure mode #10505

Priorities and Process

Add 👍 to pull requests you find important.

The Nix maintainer team uses a GitHub project board to schedule and track reviews.