I started working on a new Rails project today and it seems one of the other devs had upgraded the gem capybara-webkit to version 0.13.1.
This caused me to have issues with Qt since upgrading my Mac to Yosemite (OSX 10.10).
Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension. /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb Command 'qmake -spec macx-g++' not available Gem files will remain installed in /Users/jonnyhaynes/.bundler/tmp/14436/gems/capybara-webkit-0.13.1 for inspection. Results logged to /Users/jonnyhaynes/.bundler/tmp/14436/gems/capybara-webkit-0.13.1/./gem_make.out An error occurred while installing capybara-webkit (0.13.1), and Bundler cannot continue. Make sure that `gem install capybara-webkit -v '0.13.1'` succeeds before bundling.
I tried to install the gem manually as suggested to no avail.
A quick Google led me to here. Which had a few various solutions.
The one that worked for me was:
brew update brew install qt
I was then able to bundle without issue. Maybe it'll fix it for you too?