I’ve done a bit of research on programming fonts. Some very popular fonts cover very few glyphs. Inconsolata only has 291 for instance. If the OS fails to find the proper glyph, it will search for it in another font as this screenshot demonstrates (thank god for that feature in Chrome by the way):
Inconsolata doesn’t have the arrow glyph, but Arial does and fills in. Source Code Pro has better coverage, but also misses the arrows, so on @leedohm
’s system the same thing happens.
So what you need to know isn’t necessarily the programming font used, but it goes all the way down to the entire set of fonts available on a given system. There isn’t really a way to be sure, although most systems will have a font like Arial in there somewhere to make these glyphs show up.
If you need to be sure, and need to be sure some proportional font doesn’t mess with the measurements and code alignment/indentation (in Arial 2192 is much wider than 21a6), you could look into serving a font along with your package. There are a number of free (and very good) options that cover enormous amounts of glyphs, like DejaVu.