Custom zsh completion for a function based on default arguments

Question

How can I setup completion for a function, based on existing completion definitions and default arguments.

A simplified example (which could be rewritten as an alias

Answer 1

compdef -e 'words[1]=(git pull origin); service=git; (( CURRENT+=2 )); _git' ggl

This massages the $words, $service and $CURRENT vars used by the completion system, and then calls the _git completion function.

(Thanks to Mikachu on #zsh).