Rescue from errors during post-install rehash hook in rubygems_plugin.rb

[richiethomas]

Ruby backtick syntax does not raise exceptions if a non-zero exit code is returned by the command inside the backticks. This means we never reach inside the rescue block of rubygems_plugin.rb's hook lambda if the rbenv rehash command errors out (although we will still see any output that rbenv-rehash prints to stderr).

We can demonstrate this by purposely creating the rehash lock file, and attempting to install a gem which includes an executable:

$ touch ~/.rbenv/shims/.rbenv-shim

$ gem install wisper   
rbenv: cannot rehash: /Users/richiethomas/.rbenv/shims/.rbenv-shim exists
Successfully installed wisper-2.0.1
Parsing documentation for wisper-2.0.1
Done installing documentation for wisper after 0 seconds
1 gem installed

We can see that rbenv: cannot rehash: /Users/richiethomas/.rbenv/shims/.rbenv-shim exists printed to stderr, but the warning text, error class name, etc. inside the rescue block (i.e. rbenv: error in gem-rehash ...) is not printed.

This issue can be fixed using the Ruby standard library's Open3 module, which runs a command taken from an argument, and returns the output from stdout and stderr. If any stderr text exists, we can raise an exception with said text, and rescue with the expected warning message.

With this in place, we now see the following output:

$ gem install wisper
rbenv: error in gem-rehash (CouldNotRehashError: rbenv: cannot rehash: /Users/richiethomas/.rbenv/shims/.rbenv-shim exists
)
Successfully installed wisper-2.0.1
Parsing documentation for wisper-2.0.1
Done installing documentation for wisper after 0 seconds
1 gem installed

Note that I did also try a non-backtick invocation of rbenv rehash, i.e. system "rbenv rehash", but this similarly failed to raise an exception.

More info on Open3 here- https://docs.ruby-lang.org/en/2.0.0/Open3.html
Official module repo here- https://github.com/ruby/open3

[richiethomas]

Also note that the status variable declared is an instance of the Process::Status class, which exposes methods such as #exitstatus (returns the exit code as an int) and #success?. We could use those as well, to decide whether to raise the exception.

[richiethomas]

Closing since it appears to not be helpful.