cargo doc and linux default browser

So I recently learned about cargo doc --open while attending the Colorado Gold Rust conference. However, on my linux mint machine it opened the docs in chrome instead of my default web browser which is firefox. Since I spent most of my morning rust coding time tracking down why that was and how to fix it, I figured I write a blog post about it. So here goes:

• By looking at the cargo source, I was able to see that a separate crate named opener was used for this
• By reading the opener docs and source, I determined it runs xdg-open but not the one from my OS package manager, a separate copy it has bundled with the crate. (xdg-open is a shell script).
• I tried running xdg-open target/doc/my-crate/index.html directly on the command line and noticed it opened the wrong browser, too.
• By editing my system-level xdg-open to add set -x debugging, I was able to determine that my xdg-open was eventually calling gio open which I had never heard of.
• So I read a bunch of gio docs that said the configuration comes from a file called mimeapps.list
  • And of course, there's many locations where this file can live and both an old deprecated set of locations that is widely documented online and a new set of actual working locations with scant documentation
• I tried a bunch of wrong locations where mimeapps.list might need to be with no success
• I eventually found this Arch Wiki page that described the format and accurate location of mimeapps.list: ~/.config/mimeapps.list
• In there I found a bunch of stuff and every time I saw google-chrome.desktop I just preceeded it with firefox.desktop; and that seemed to work