vivaldi: missing meta.mainProgram

[YahiaJr]

Bug Description

Whenever lib.getExe is used with vivaldi to set it's binary path into a session variable for example, it produces a big warning stating that the meta.mainProgram attribute is missing and it will default to package name.

Steps To Reproduce

1. Use a library function that needs the attribute meta.mainProgram like lib.getExe the vivaldi package as below:

home.sessionVariables = { 
      DEFAULT_BROWSER = lib.getExe pkgs.vivaldi;
      BROWSER = lib.getExe pkgs.vivaldi;
};

3. Then rebuild the config: sudo nixos-rebuild switch --flake .#<HOSTNAME>
4. During the build process a big warning will appear stating the following:

trace: warning: getExe: Package "vivaldi-6.7.3329.41" does not have the meta.mainProgram attribute. 
We'll assume that the main program has the same name for now, but this behavior is deprecated, because it leads to surprising errors when the assumption does not hold. 
If the package has a main program, please set `meta.mainProgram` in its definition to make this warning go away. 
Otherwise, if the package does not have a main program, or if you don't control its definition, use getExe' to specify the name to the program, such as lib.getExe' foo "bar".

Notify maintainers

@otwieracz , @badmutex 👋👋

Workaround For Now

Do the hint stated in the warning and use it like:

home.sessionVariables = { 
      DEFAULT_BROWSER = lib.getExe' pkgs.vivaldi "vivaldi";
      BROWSER = lib.getExe' pkgs.vivaldi "vivaldi";
};