Invoke chruby_auto before the prompt prints in interactive mode

[postmodern]

@zendeavor points out that it is confusing to users that chruby_auto is invoked before the command is executed and before the prompt is printed. If user's (ex: @jc00ke) include $RUBY_ENGINE and $RUBY_VERSION in their $PS1, then these values wont be updated until the command after the cd command is executed. @zendeavor recommends using different hooking strategies for interactive vs. non-interactive modes.

Interactive

• bash: PROMPT_COMMAND
• zsh: precmd_functions
• ksh: PS1

Non-interactive

• bash: trap DEBUG
• zsh: preexec_functions
• ksh: trap DEBUG

This would invoke chruby_auto before PS1 is rendered in interactive mode, but invoke chruby_auto before the command is even executed in non-interactive mode.

[zendeavor]

ksh would be a Discipline function for interactive mode, and potentially for non-interactive use as well. sticking chruby_auto into $PS1 will cause equally surprising and maybe hard to debug behaviour in the case that chruby_auto fails; the stderr might get printed directly into PS1 (ugly and surprising) or it might be discarded entirely (hard to debug)

[regularfry]

Would it be total heresy to suggest that chruby_auto is a misfeature? Automatically running stuffs on cd is all well and good, but it's fairly well-handled by, for instance, http://github.com/kennethreitz/autoenv. Given that this responsibility can be punted to another tool, shouldn't we do that rather than complicate chruby?

[postmodern]

Auto-switching was a much requested feature. We put it in a separate file so as not to force it upon the other users. Implementing auto-switching "correctly" is tricky. For example autoenv merely hooks cd (tsk tsk), which will miss things such as git pull or git checkout other_branch.

[zendeavor]

function chruby_preexec_bash_set {                                              
  typeset -a hook                                                               
  typeset trap=$(trap -p DEBUG)                                                 
  if [[ $1 == -r ]]; then                                                       
    PROMPT_COMMAND=${PROMPT_COMMAND//chruby_auto?}                              
    IFS=\' read -ra hook <<<"$trap"                                             
    IFS=\; read -ra hook <<<"${hook[@]:1:${#hook[@]}-2}"                        
    trap "${hook[@]//chruby_auto?}" DEBUG                                       
  fi                                                                            
  [[ $PROMPT_COMMAND == *chruby_auto* || $(trap -p DEBUG) == *chruby_auto* ]] &&
    chruby_preexec_bash_set -r                                                  
  if [[ $- == *i* ]]; then                                                      
    IFS=\; read -ra hook <<<"$PROMPT_COMMAND"                                   
    PROMPT_COMMAND="${hook[@]/%/;} chruby_auto"                                 
  else                                                                          
    IFS=\' read -ra hook <<<"$trap"                                             
    IFS=\; read -ra hook <<<"${hook[@]:1:${#hook[@]}-2}"                        
    trap "${hook[@]/%/;} chruby_auto" DEBUG                                     
  fi                                                                            
}

updated with some basic hook-removal logic
updated again with a bit of deduplication. there's some more redundancy left, but i don't see a clean way to handle it without polluting the function namespace with a stupidly complicated chruby_read_hook that no one would ever use for anything in the world.

[zendeavor]

i admit there's probably quite a bit of magic happening in a black hole with the above code but it's pretty much implementation detail. this method removes the need for some really arcane parameter expansions and should Just Work™ but it may need a little bit of extra error checking to make sure ${hook[@]} isn't empty before we use it directly.

[edlebert]

$_ is also broken in bash with chruby_auto. It always returns chruby_auto

~ $ echo $_
chruby_auto

[2called-chaos]

I don't if this is exactly related so tell me if I should create a new issue for this. I've set my OS X Terminal to cd into the current directory when opening a new tab. This happens:

Last login: Wed Jan 15 15:53:58 on ttys000
You have new mail.
cd "/Volumes/code/_cont/etn-intranet" && clear
chruby: unknown Ruby: 1.9.3-p327-perf
/Volumes/code/_cont/etn-intranet[master]$ cd "/Volumes/code/_cont/etn-intranet" && clear

chruby-auto seems to hook (ruby 2 is default, 1.9 is in .ruby-version) but it doesn't recognize the version at this point. When I put export RUBIES=(~/.rbenv/versions/*) before source '/usr/local/share/chruby/auto.sh' it won't have this error but it also doesn't switch effectively failing silently...

[caleb]

In my ZSH configuration, I use this to move chruby_auto to precmd:

if [[ $PS1 ]]; then
  precmd_functions+=("chruby_auto")
  preexec_functions=${preexec_functions:#"chruby_auto"}
fi

This seems to work for me, and fixes the problem of my prompt not updating when I first cd to a directory with a .ruby-version file. This is because preexec_functions are executed before a command is executed. Whereas precmd_functions get executed before the prompt is printed.

It would be nice to see this change at least for ZSH in chruby. I don't know anything about bash, and I suppose I could be missing something with this ZSH configuration, but it works for me.

[swrobel]

Thank you, @caleb for that workaround! Adding my +1 for seeing this added to chruby.

[FranklinYu]

I wonder whether we need to detect interactive shell in auto.sh. As far as I understand, auto.sh is only intended for interactive shell; non-interactive shell should use chruby-exec which only uses chruby.sh.

In addition, I feel like it’s more elegant to use the Zsh builtin add-zsh-hook, like

add-zsh-hook -d preexec chruby_auto
add-zsh-hook precmd chruby_auto

where -d means “delete”.