Using homebrew.casks in nix-darwin reporting "Brewfile dependency failed to install"

[yzhou216]

When installing casks using homebrew-casks from nix-darwin, the program successfully installs, but reporting "Brewfile dependency failed to install" (xcrun command). This happens even with xcodebuild installed:

lrwxr-xr-x 1 root wheel 74 Dec 31  1969 /run/current-system/sw/bin/xcrun -> /nix/store/mvwzcsdjgxw0qp531frxz07mnsh4mryx-xcodebuild-0.1.2-pre/bin/xcrun

Here's an example of attempting to install iTerm2:

Installing iterm2
==> Downloading https://iterm2.com/downloads/stable/iTerm2-3_5_3.zip
Warning: macOS's Gatekeeper has been disabled for this Cask
==> Installing Cask iterm2
==> Moving App 'iTerm.app' to '/Applications/iTerm.app'
🍺  iterm2 was successfully installed!
Error: No developer tools installed.
Install the Command Line Tools:
  xcode-select --install

Installing iterm2 has failed!
Homebrew Bundle failed! 1 Brewfile dependency failed to install.