$ nix-env -i mercurial
warning: there are multiple derivations named 'mercurial-5.6'; using the first one
installing 'mercurial-5.6'
nix-env: src/libexpr/attr-set.hh:54: void nix::Bindings::push_back(const nix::Attr&): Assertion `size_ < capacity_' failed.

src/nix-env/user-env.cc:93
93              for (auto & j : metaNames) {
1: metaNames = std::set with 17 elements = {[0] = "available", [1] = "broken", [2] = "description", [3] = "downloadPage", [4] = "homepage",
  [5] = "insecure", [6] = "isBuildPythonPackage", [7] = "license", [8] = "maintainers", [9] = "name", [10] = "outputsToInstall", [11] = "platforms",
  [12] = "position", [13] = "unfree", [14] = "unsupported", [15] = "updateWalker", [16] = "version"}