Adapted from the method used by TextMate, this library provides
a command ruby-hash-syntax-toggle which attempts to automatically
convert the selected region of ruby code between 1.8 and 1.9 hash styles.
If you choose not to use one of the convenient packages in
MELPA, you'll need to add the
directory containing ruby-hash-syntax.el to your load-path, and then
(require 'ruby-hash-syntax).
Add the following to your emacs init file:
(require 'ruby-hash-syntax)
Then select a block of ruby code containing a hash literal (perhaps
using mark-sexp), and run the ruby-hash-syntax-toggle command:
M-x ruby-hash-syntax-toggle
You might like to bind that command to a key in ruby-mode-map.