Setting environment variables from within snapcraft.yaml

[Joseph Rushton Wakeling]

Hello folks,

Is it possible to set environment variables to be used when creating a part of a 
snap?

I guess one could use the `prepare:` scriptlet to do something like `export 
MY_VAR=whatever` but I'd like the environment variable to be set before I even 
pull the source.  (If you're wondering why: I'm considering whether I can use 
git environment variables to work around the launchpad-buildd constraints on 
support for git:// URLs.)

I'm not seeing anything relevant in https://snapcraft.io/docs/build-snaps/parts, 
hence why I ask here.

Thanks & best wishes,

     -- Joe