Was I going crazy, or was Emacs displaying certain text too wide?

Symptoms

Most the problems I observed was when using emacs ansi-term, but they can happen anywhere the Emacs Mac OS X application is displaying Unicode characters.

Oddly wide  dashes (em dashes is the publishing terminology).

Too Wide Em-Dash Amongst Monospaced Text

Lines wrapping, output Unexpectedly Wrapping Beyond the Bottom of the Emacs Windows, and Black Boxes

Lines Wrapping When They Shouldn’t

Root Cause

It took me a long time to figure out:

1. That I wasn’t going crazy.
2. The root cause.

To make a long story short, I had stumbled across Emacs Bug 11450 – Fallback Font Used Even When Available in Primary Font which can be translated as: “fancy characters don’t display correctly using the Mac OS X Emacs application.”

Solution

The solution boils down to adding this snippet to your emacs init file (aka .emacs file):


(when (eq window-system 'ns)
(set-default-font "Monaco")
(set-fontset-font "fontset-default" 'symbol "Monaco")))

Note: You may want to choose a different default font other than Monaco.