neat prompt hack: mark non-exported var

[Phil Pennock <zsh-workers+phil.pennock@xxxxxxxxxxxx>]

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For some colleagues who use oh-my-zsh, I just constructed a prompt theme
which references a variable which needs to be exported into the
environment.  There's a neat part which (IMO) makes it worth sharing
outside of oh-my-zsh.

This is based on the existing 'cloud' theme; the key is that if
$APC_HOME is set, it overrides $HOME for looking up some tool data, and
staff here touch multiple clouds so actually use this feature.  (Our
customers would not).  So the idea is to show the cloud, and _which_
cloud, assuming that the last part of $APC_HOME is the cloud name.

The particularly neat part is the addition of warning signs if APC_HOME
is set but not exported; since the whole point of the var is to
influence a binary command outside the shell, this is almost certainly a
mistake.  I was thinking in terms of using a ternary operator and
something from zsh/parameters, before realising zsh/parameters doesn't
have a table for exported vars.  Realising that it could _all_ be done
with :+ substitutions based on ${(t)APC_HOME} marking 'scalar' vs
'scalar-export' made it easy (albeit slightly intricate in quoting
because the '}' in '%}' was claimed by the '${' if not protected).

Perhaps this mechanism to warn of non-exported control variables in the
prompt will be useful to others?

Regards,
- -Phil

- ---------------------8< apcera-cloud.zsh-theme >8-----------------------
: ${ZSH_THEME_CLOUD_PREFIX:='☁'}
# not :=, allow it to be empty:
: ${ZSH_THEME_CONTINUUM_SEPARATOR='→'}
: ${ZSH_THEME_CONTINUUM_APCNOTEXPORTED:='⚠⚠⚠'}
: ${ZSH_THEME_CONTINUUM_COLOR:=magenta}

if [[ -z $ZSH_THEME_CONTINUUM_PREFIX ]]; then
    ZSH_THEME_CONTINUUM_PREFIX='${APC_HOME:+"${ZSH_THEME_CONTINUUM_SEPARATOR}%{$fg_bold[${ZSH_THEME_CONTINUUM_COLOR}]%}"}'
    ZSH_THEME_CONTINUUM_PREFIX+='${(U)${APC_HOME:t}[1]}${(L)${APC_HOME:t}[2,-1]}'
    ZSH_THEME_CONTINUUM_PREFIX+='${APC_HOME:+"%{$reset_color%}"}'
# This ensures that we put in a big warning if APC_HOME is not exported to environ:
    ZSH_THEME_CONTINUUM_PREFIX+='${APC_HOME:+"${${${(t)APC_HOME}#scalar-export}:+"%{$fg_bold[red]%}${ZSH_THEME_CONTINUUM_APCNOTEXPORTED}%{$reset_color%}"}"}'
fi

PROMPT='%{$fg_bold[cyan]%}${ZSH_THEME_CLOUD_PREFIX}%{${reset_color}$fg[cyan]%}'"${ZSH_THEME_CONTINUUM_PREFIX}"
PROMPT+=' %{$fg_bold[green]%}%p %{$fg[green]%}%c %{$fg_bold[cyan]%}$(git_prompt_info)%{$fg_bold[blue]%} % %{$reset_color%}'

ZSH_THEME_GIT_PROMPT_PREFIX="%{$fg[green]%}[%{$fg[cyan]%}"
ZSH_THEME_GIT_PROMPT_SUFFIX="%{$reset_color%}"
ZSH_THEME_GIT_PROMPT_DIRTY="%{$fg[green]%}] %{$fg[yellow]%}⚡%{$reset_color%}"
ZSH_THEME_GIT_PROMPT_CLEAN="%{$fg[green]%}]"
- ----------------------------8< cut here >8------------------------------

(Derived from cloud.zsh-theme, part of oh-my-zsh, which is
 MIT-licensed).
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