improve command map combined with prefix

[mikz]

It is valid use case to set both command map and prefix.
In case of using different binary, the map should still be active and prefixed.

Includes and closes #310.

Will squash the commits when we agree that it makes sense.

It changes prefix to generate: bundle exec /usr/bin/env rake instead of bundle exec rake.
Would that be a breaking change?

[mattbrictson]

I think this could break capistrano-rbenv. It adds the prefix $HOME/.rbenv/bin/rbenv exec, and this would happen:

$HOME/.rbenv/bin/rbenv exec /usr/bin/env rake
rbenv: /usr/bin/env: command not found

[mikz]

@mattbrictson will check, thanks!

I'd expect rbenv exec to behave like bundle exec. Running any executable file with different environment. https://github.com/rbenv/rbenv/blob/a95ccd09a2c7cff435d915756abd5a2fe096fb9d/libexec/rbenv-exec looks like does exactly that, just prepares environment and calls exec.

I think running anything in /usr/bin/env should be harmless.

[leehambley]

So did we think we would merge this? This would also solve #299 which I'd be glad of, reading the notes here from you both it looks like the rbenv issue was not really an issue?

[mattbrictson]

I believe rbenv exec is still a problem. Last I heard, @mikz was going to look into it some more.

[mikz]

@mattbrictson the example in #311 (comment) should fail also locally, right?

$ rbenv exec /usr/bin/env ruby -v
ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin15]

Works just fine for me.

We are using this patch in production for few weeks and successfully migrated to ruby 2.2 with this.

[mikz]

Rebased this to be mergeable again.

@mattbrictson I really don't have any server with rbenv. If you have any, could you try to do a deploy with this? I tried those commands locally and all works. From all the source code, it should be just fine. Wrapping a command in /usr/bin/env, rbenv exec or bundle exec does the same thing. Just adds environment and execs that command. All those can be chained together as they just modify the env.

[leehambley]

I'll see if I can check now.

[mattbrictson]

Unfortunately it doesn't work in my local environment (OS X).

$ rbenv exec /usr/bin/env ruby -v
rbenv: /usr/bin/env: command not found
$ rbenv --version
rbenv 1.0.0
$ bash --version
GNU bash, version 4.3.42(1)-release (x86_64-apple-darwin14.5.0)

[mattbrictson]

Just to prove it works without the rbenv exec part:

$ /usr/bin/env ruby -v
ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin14]

[mikz]

@mattbrictson that is so weird. It works for me. Also rbenv 1.0.0. Both in zsh and bash.

GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin15)

zsh 5.0.8 (x86_64-apple-darwin15.0)

I edited by /usr/local/Cellar/rbenv/1.0.0/libexec/rbenv-exec and added there echo at the line before the exec and here is output for some commands i tried:

$ rbenv exec ruby -v                                                                                                                                                                        ruby-2.3.0
exec -a ruby /Users/mikz/.rvm/rubies/ruby-2.3.0/bin/ruby -v
ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin15]

$ rbenv exec bash --version                                                                                                                                                                 ruby-2.3.0
exec -a bash /bin/bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin15)

$ rbenv exec env bash --version                                                                                                                                                             ruby-2.3.0
exec -a env /usr/bin/env bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin15)

$ rbenv exec /usr/bin/env bash --version                                                                                                                                                    ruby-2.3.0
exec -a /usr/bin/env /usr/bin/env bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin15)

I really don't see how that could fail. Could you also try running:

exec -a /usr/bin/env /usr/bin/env bash --version
exec /usr/bin/env bash --version
exec -a /usr/bin/env /usr/bin/env ruby --version

I have no idea how to reproduce this. That really should not happen AFAIK.

[mattbrictson]

Well, clearly something strange is going on. My own OS X machine fails (rbenv installed via Homebrew), and other Ubuntu VMs that I have also fail (rbenv installed via Git clone). However, just now I provisioned a brand new Ubuntu 14.04 VM, installed rbenv, and rbenv exec works fine there.

Perhaps it is a certain rbenv plugin that is causing issues, but I'm grasping at straws here. I'll try to figure it out.

[mattbrictson]

I've narrowed it down: rbenv fails and prints command not found on when it reaches this line: https://github.com/rbenv/rbenv/blob/e851250da66307a2584218b555068c941b493d44/libexec/rbenv-exec#L33

[mikz]

So: rbenv which /usr/bin/env fails for you? What about rbenv which env ?

Could you try to run it with RBENV_DEBUG=1 ?

Internally it is using command like: command -v /usr/bin/env (no message, just error code).

There are some script inclusions, that could affect it. It is hard to help when I can't make it fail.

edit:
it looks like it has to be there: https://github.com/rbenv/rbenv/blob/e851250da66307a2584218b555068c941b493d44/libexec/rbenv-which#L52-L58

[mattbrictson]

OK, if you look here: https://github.com/rbenv/rbenv/blob/e851250da66307a2584218b555068c941b493d44/libexec/rbenv-which#L38-L43

Then you'll see that rbenv-which only searches the PATH if the current version is system. Otherwise rbenv will search the bin directory of the current Ruby version, which of course doesn't have a binary named env or bash.

Example:

$ rbenv version
2.3.0 (set by /Users/mbrictson/.rbenv/version)
$ rbenv which /usr/bin/env
rbenv: /usr/bin/env: command not found
$ rbenv which env
rbenv: env: command not found

But if I switch to system, then:

$ rbenv shell system
$ rbenv which /usr/bin/env
/usr/bin/env
$ rbenv which env
/usr/bin/env

Long story short, it only works if you don't have a default version set (and are therefore using the system version).

[mikz]

So. You cannot run ANY command that is not provided by ruby, via rbenv exec ? Wow.

Ok. Guess that is not going away no matter how wrong it is.

Lets figure out a way to disable this in the capistrano-rbenv plugin? Would you think that would be the right place to do so?

[mattbrictson]

Honestly I'm not sure how to approach this. I don't use capistrano-rbenv in production, so I'm probably not a good person to give advice.

But to recap: my understanding is that capistrano-rbenv prefixes known Ruby binaries (e.g. rake, bundler) with rbenv exec. If these are not mapped, then SSHKit's default map comes into play, which is to add /usr/bin/env. And so (with this PR) you end up with rbenv exec /usr/bin/env rake, which fails.

There isn't really an SSHKit API to disable the default env mapping, except to add a new mapping. So I suppose capistrano-rbenv could add a "noop" mapping for the known Ruby binaries. But then that would clobber any user-provided mappings.

I don't see a way out. What's your take?