Support .dmg.bz2 and other containerless compressed disk images

[lachlancooper]

I'm trying to install git-annex on OSX 10.8.2, where for some reason the upstream .dmg is compressed with bz2. The existing cask can't handle this, it fails with:

lachlan@velasco:~$ brew cask install git-annex
==> Caveats
Cask git-annex installs files under "/usr/local".  The presence of such
files can cause warnings when running "brew doctor", which is considered
to be a bug in homebrew-cask.

==> Downloading http://downloads.kitenet.net/git-annex/OSX/current/10.8.2_Mountain_Lion/git-annex.dmg.bz2
######################################################################## 100.0%
Error: It seems the symlink source is not there: '/opt/homebrew-cask/Caskroom/git-annex/latest/git-annex.app'

After investigating a bit I discovered nested_container and tried adding a suitable line to the cask, but now it fails in a different way:

lachlan@velasco:~$ brew cask install git-annex
==> Caveats
Cask git-annex installs files under "/usr/local".  The presence of such
files can cause warnings when running "brew doctor", which is considered
to be a bug in homebrew-cask.

==> Downloading http://downloads.kitenet.net/git-annex/OSX/current/10.8.2_Mountain_Lion/git-annex.dmg.bz2
######################################################################## 100.0%
Error: No such file or directory - /opt/homebrew-cask/Caskroom/git-annex/latest/git-annex.dmg

I haven't really looked into how nested_container works, but I'd guess this is failing because unlike, say, zip and tar.gz, bz2 and gz aren't really containers and don't contain filenames or other metadata; they're just the plain disk image file, compressed.

This issue is pretty low priority, since git-annex seems to be the only cask affected by the problem.

[rolandwalker]

Hi! Thanks for the report!

Yes, hdiutil chokes here and refuses to recognize the DMG, because the URL is downloaded into a file which lacks the .dmg ending.

This problem is addressed by the addition of a :target key to the url stanza in #3043, which is unfortunately not finished. If that PR remains unfinished much longer, I may spin out the :target logic into a separate patch.

Luckily, there is a hack we can use to make this Cask work for the moment.