This cannot happen without a full Xcode install, and that is dumb. Also there's no way (at present) to check for it, auto-install it, or even mention it. At the least, the README should be updated.

cc @jbarnette

With no pre-existing MacVim on my system I saw the following errors:

Error: Could not set 'present' on ensure: Failed running sudo -E -u olivierlacan /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim at 12:/opt/boxen/repo/shared/macvim/manifests/init.pp
Error: Could not set 'present' on ensure: Failed running sudo -E -u olivierlacan /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim at 12:/opt/boxen/repo/shared/macvim/manifests/init.pp
Wrapped exception:
Failed running sudo -E -u olivierlacan /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim
Error: /Stage[main]/Macvim/Package[macvim]/ensure: change from absent to present failed: Could not set 'present' on ensure: Failed running sudo -E -u olivierlacan /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim at 12:/opt/boxen/repo/shared/macvim/manifests/init.pp

Let me know if I can help diagnose what may be causing this.

I did a pretty standard install of boxen, everything seemed to work (including other homebrew packages), but when I tried to add MacVim, boxen would fail like this:

andre ~/sw/boxen master $ ./script/boxen
Boxen has unpushed commits on master, won't auto-update!
sh: /opt/boxen/repo/vendor/puppet/source/8c245d77095e501cccea2065510af8a8e88070a0.tar.gz: No such file or directory
Notice: Package[macvim](provider=homebrew): Updating homebrew formulas
Error: Could not set 'present' on ensure: Failed running sudo -E -u andre /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim at 12:/opt/boxen/repo/shared/macvim/manifests/init.pp
Error: Could not set 'present' on ensure: Failed running sudo -E -u andre /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim at 12:/opt/boxen/repo/shared/macvim/manifests/init.pp
Wrapped exception:
Failed running sudo -E -u andre /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim
Error: /Stage[main]/Macvim/Package[macvim]/ensure: change from absent to present failed: Could not set 'present' on ensure: Failed running sudo -E -u andre /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim at 12:/opt/boxen/repo/shared/macvim/manifests/init.pp

Manually running the homebrew command in question would fail like this:

$ sudo -E -u andre /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim
==> Downloading https://github.com/b4winckler/macvim/tarball/snapshot-66
######################################################################## 100.0%
==> ./configure --with-features=huge --with-tlib=ncurses --enable-multibyte --with-macarchs=x86_64 --enable-perlinterp --enable-pythoninterp --enable-rubyinterp --enable-tclinterp -
==> make getenvy
==> make
Error: src/MacVim/build/Release/MacVim.app does not exist

Some googling led me to a homebrew ticket where someone suggested running this:

$ sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer/

After running that, everything worked perfectly. You might want to add a note to the readme?

On my machine, if I run boxen again after adding this include I get the following errors:

Error: Execution of 'brew switch macvim 7.3-66' returned 1: Cleaning /opt/boxen/homebrew/Cellar/macvim/7.3-66
Warning: Could not link macvim. Unlinking...
Error: Could not symlink file: /opt/boxen/homebrew/Cellar/macvim/7.3-66/bin/vimdiff
Target /opt/boxen/homebrew/bin/vimdiff already exists. You may need to delete it.
To force the link and overwrite all other conflicting files, do:
brew link --overwrite formula_name

To list all files that would be deleted:
brew link --overwrite --dry-run formula_name

Error: /Stage[main]/Macvim/Package[macvim]/ensure: change from absent to present failed: Execution of 'brew switch macvim 7.3-66' returned 1: Cleaning /opt/boxen/homebrew/Cellar/macvim/7.3-66
Warning: Could not link macvim. Unlinking...
Error: Could not symlink file: /opt/boxen/homebrew/Cellar/macvim/7.3-66/bin/vimdiff
Target /opt/boxen/homebrew/bin/vimdiff already exists. You may need to delete it.
To force the link and overwrite all other conflicting files, do:
brew link --overwrite formula_name

To list all files that would be deleted:
brew link --overwrite --dry-run formula_name

When doing a boxen run to install macvim, the following error is thrown:

MountainLionClient:repo admin$ boxen Warning: Config file /tmp/boxen/puppet/conf/hiera.yaml not found, using Hiera defaults Notice: Package[macvim](provider=homebrew): Updating homebrew formulas Error: Could not set 'present' on ensure: Failed running sudo -E -u admin /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim at 12:/opt/boxen/repo/shared/macvim/manifests/init.pp Error: Could not set 'present' on ensure: Failed running sudo -E -u admin /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim at 12:/opt/boxen/repo/shared/macvim/manifests/init.pp Wrapped exception: Failed running sudo -E -u admin /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim Error: /Stage[main]/Macvim/Package[macvim]/ensure: change from absent to present failed: Could not set 'present' on ensure: Failed running sudo -E -u admin /opt/boxen/homebrew/bin/brew boxen-install macvim --with-cscope --override-system-vim at 12:/opt/boxen/repo/shared/macvim/manifests/init.pp MountainLionClient:repo admin$

This is a plain 10.8.2 install on a VM.

When I run boxen, I get the following warning. How can I solve it?

$ script/boxen
Boxen has a dirty tree, won't auto-update!
Warning: Config file /tmp/boxen/puppet/conf/hiera.yaml not found, using Hiera defaults