Here's zsh snippet I've came up with for my own simple functions. I'm using it as a base for other completions. In this example, function `set-java-home zulu-21` sets JAVA_HOME to `~/apps/java/zulu-21`. Here's `_set-java-home`:

    #compdef set-java-home
    
    local -a versions=(~/apps/java/*(:t))
    _describe 'version' versions

So basically almost a one-liner (but couldn't do it really one-liner, unfortunately).