zsh: switch rubies after changing pwd, not before

[nathanl]

I suspect this PR will be rejected as "you misunderstand" or will need improving. Here's the problem I'm trying to solve: auto.sh hooks preexec to try to set the correct ruby before running a command. If that command is something like cd, running before the command means it finds .ruby-version from the folder I'm leaving, not from the folder I'm entering.

Setup

• use zsh
• mkdir -p switching_test/sub
• echo 'ruby-top' > switching_test/.ruby-version
• echo 'ruby-sub' > switching_test/sub/.ruby-version

  Tests

• cd switching_test
  • Expected result: chruby: unknown Ruby: ruby-top
  • Actual result: no error
• cd sub
  • Expected result: chruby: unknown Ruby: ruby-sub
  • Actual result: chruby: unknown Ruby: ruby-top

    This fix

If we also use the chpwd hook, we'll switch rubies a second time when we arrive in the new directory. It's not a perfect fix, but at least the end result is correct.

Imperfections:

• Unnecessary work
• If switching out of a folder with an invalid ruby version, the user will see an error like chruby: unknown Ruby, even though we immediately afterwards switch to the right version.

  Misgivings

• You list "does not hook CD" as an anti-feature. Do you consider this hooking CD? It doesn't mess with the actual command; eg, it works with pushd and popd.
• I'm not sure how to run the tests properly, much less add one; test/runner gives me a bunch of errors with backtraces like /usr/share/shunit2/shunit2:.:129: no such file or directory: /usr/share/shunit2/shunit2 \n test/chruby_auto_test.sh:zsh:130: use 'exit' to exit. I installed chruby with homebrew and it appears to be looking in the installation folder for shunit2, but I don't know why.

  Alternate idea

The README describes auto-switching as being useful for "when you cd between your different projects". A chpwd hook handles exactly that scenario, and the preexec hook isn't great for it, because it creates the problem I've described here.

But preexec is nice for when you open a new terminal and run a command; it ensures you're on the right Ruby first.

Is that the only scenario we need it for? If so, wouldn't it be more straightforward to find a way to run chruby_auto when a new terminal is spawned? Eg, maybe we could use a precmd hook that removes itself in that shell after running chruby_auto, and subsequently leaves it to the chpwd hook?

What do you think?

[postmodern]

Any changes to auto-switching should be mirrored for bash as well as zsh. Also behavior should remain consistent for non-interactive as well as interactive sessions.

[nathanl]

@postmodern After some research, I don't see a way to mimic zsh's chpwd_functions in bash.

I understand that you want zsh and bash to work the same way out of the box, but zsh supports a usage that is (in my opinion) much nicer.

What would you think about a change like this?

• From auto.sh, extract auto_function.sh. Then auto.sh would source ./auto_function.sh before setting up its hooks and would continue to work the same way.
• However, users like me would then have the option to source auto_function.sh and either 1) run it manually as desired or 2) set up alternate hooks, like chpwd_functions in zsh.

[nathanl]

Ah, geez. Apparently "source another script in the same folder as this one" is harder than it sounds. I give up. I'm going to copy and paste auto.sh into my dotfiles and modify it as I see fit.

[postmodern]

Yep, I think our hands are tied by the shell. We have to maintain behavior between Bash and Zsh. OSX still ships Bash 3, so we can't even take advantage of Bash 4 features. We tried using PROMPT_COMMAND in the past, but injecting into it was error prone.