fish-shell/share/completions/env.fish

function __fish_complete_env_subcommand
    argparse -s s/ignore-environment u/unset h-help v-version -- (commandline -opc) (commandline -ct) 2>/dev/null
    or return

    # argv[1] is `env` or an alias.
    set -e argv[1]

    # Remove all VAR=VAL arguments up to the first that isn't
    while set -q argv[1]
        if string match -q '*=*' -- $argv[1]
            set -e argv[1]
        else
            break
        end
    end

    # Then complete the rest as if it was given as a command.
    if set -q argv[1]
        complete -C"$argv"
        return 0
    end
    return 1
end

# Files aren't useful with env. They are correctly suggested with the command.
complete -c env -f

complete -c env -a "(__fish_complete_env_subcommand)" # -d "Command"

complete -c env -n 'not __fish_complete_env_subcommand' -a "(set -n)=" -x -d "Redefine variable"
complete -c env -n 'not __fish_complete_env_subcommand' -s i -l ignore-environment -d "Start with an empty environment"
complete -c env -n 'not __fish_complete_env_subcommand' -s u -l unset -d "Remove variable from the environment" -x -a "(set -n)"
complete -c env -n 'not __fish_complete_env_subcommand' -l help -d "Display help and exit"
complete -c env -n 'not __fish_complete_env_subcommand' -l version -d "Display version and exit"