Here are the changes to add bash completion support to latexmk. I also sent the file to John Collins
Created attachment 234949 [details, diff] patch for latexmk-416a.ebuild
Created attachment 234951 [details] the bash completion module itself
applied, thanks please also send this to the latexmk author, it'd be nice to see it included in the official distribution and btw, you dont need to override pkg_postinst for calling the bash-completion postinst as its exported from the eclass