Some of the theme-related functions defined in lib/git.zsh call current_branch. But current_branch is only defined in the git plugin. So if that plugin is not loaded, themes which use these functions will produce an error like git_prompt_ahead:1: command not found: current_branch each time the prompt is issued.

Functions affected:

• git_prompt_ahead()
• git_prompt_behind()
• git_prompt_remote()

Themes affected:

➜  .oh-my-zsh git:(master) egrep -r -l 'git_prompt_(ahead|behind|remote)' themes/*
themes/juanghurtado.zsh-theme
themes/sunrise.zsh-theme
themes/wedisagree.zsh-theme
➜  .oh-my-zsh git:(master) grep -rl current_branch themes/*
themes/eastwood.zsh-theme
themes/gallois.zsh-theme
themes/josh.zsh-theme
themes/juanghurtado.zsh-theme
themes/mortalscumbag.zsh-theme
themes/peepcode.zsh-theme
themes/sunrise.zsh-theme

I don't think the core stuff should depend on plugins, or at least, it should be an optional, declared dependency.

Workaround is to load the git plugin. Easy enough, but I don't think it should be required.

The current_branch() function definition should probably be moved from the git plugin to the core lib/git.zsh to remove this plugin dependency. Possibly, it should be renamed (e.g. to git_current_branch) to make it clear that it's for Git and not Mercurial or Bazaar or whatever, and a current_branch back-compatibility wrapper left in the git plugin.

Caused #4059.
Caused #4084.
Probably caused #2193.
Caused #331.
Caused by #329, in part.
Caused by #2723 (in #3809).

Fixed by #2386, I think, but that PR has a lot of other stuff going on, too, and has been sitting for 18 months without getting merged. Should probably do a smaller, easier-to-review patch to fix this issue independently.