I have a problem with Homebrew editor: Atom is used instead of Vim
$ brew edit a_brew_formula
Editing /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/a_brew_formula.rb
Warning: Using atom because no editor was set in the environment.
This may change in the future, so we recommend setting EDITOR,
or HOMEBREW_EDITOR to your preferred text editor.
EDITOR and HOMEBREW_EDITOR are well set in config.fish:
set EDITOR vim
set HOMEBREW_EDITOR vim
I checked in the shell:
$ echo $EDITOR
vim
Why my editor choice is not taken into account?
You haven't exported the variable, so external processes (like homebrew) don't see it.
Use set -x, but preferably set -gx to also define global scope on the variable.
E.g.
set -gx EDITOR vim
To see what an external process sees, you can use env. If called without arguments, it will print its environment as VAR=VALUE lines.
If that doesn't show EDITOR=, you know that you've not exported your $EDITOR.