ansible/ansible — pull request #1080 by dagwieers (2012-09-24 19:11:17+00:00)
Title: Add an only_if option to vars_prompt to make prompts conditional

Sometimes you may want to allow variables through host_vars or inventory, but prompt for a value if it is not set or if the value does not conform to something specific. This option allows you to specify when you want to offer a prompt.