Warn if ruby/rails/bundle binstub shebangs are bad

[calebhearth]

Binstubs, which RubyGems and Bundler generate to prepare the environment
before dispatching calls to original executables, can sometimes include
shebangs that worked on developer machines, but won't work on Heroku.
Often, this is caused by ruby binaries being named other than ruby (or
ruby.exe on Windows).

While it can happen for any binstub, we're mostly concerned about
rake, rails, and bundler stubs. Check each of these to see if they
are !#/usr/bin/env ruby or !#/usr/bin/env ruby.exe and issue a
warning if this is not the case.

[schneems]

I think we need to move the logic to a different place.

We could update one of the existing integration tests with a bad looking binstub that actually still works like

#!/usr/bin/env ruby #bad-binstub

And then assert the output on deploy in one of the existing Hatchet tests matched the string #bad-binstub. That way we could be sure that the change was being tested.

[schneems]

Is this the right file to add this logic? We use this to installer to download the version of Ruby that the buildpack bootstraps with.

It gets called here

heroku-buildpack-ruby/bin/support/download_ruby

Line 12 in a46dcce

installer = LanguagePack::Installers::HerokuRubyInstaller.new(ENV['STACK'] || DEFAULT_STACK)

and that gets called from this script

heroku-buildpack-ruby/bin/support/bash_functions.sh

Line 35 in a46dcce

$bin_dir/support/download_ruby $heroku_buildpack_ruby_dir

which is executed in a few places

https://github.com/heroku/heroku-buildpack-ruby/search?utf8=%E2%9C%93&q=heroku_buildpack_ruby_install_ruby&type=

I don't think we're inside of the right directory either.

[schneems]

I would like a link to that devcenter article you wrote here. If you give me the link I can edit it and give some feedback as well.

[schneems]

This is the main flow for the compile action

heroku-buildpack-ruby/lib/language_pack/ruby.rb

Lines 91 to 114 in cebdf68

	def compile
	instrument 'ruby.compile' do
	# check for new app at the beginning of the compile
	new_app?
	Dir.chdir(build_path)
	remove_vendor_bundle
	warn_bundler_upgrade
	install_ruby
	install_jvm
	setup_language_pack_environment
	setup_export
	setup_profiled
	allow_git do
	install_bundler_in_app
	build_bundler("development:test")
	post_bundler
	create_database_yml
	install_binaries
	run_assets_precompile_rake_task
	end
	best_practice_warnings
	super
	end
	end

If we can't find a good place to shoe-horn in another check, one option is to add a new method like warn_bad_binstubs.

The trick is we want to do this before any errors could crop up that might arise from the thing we're warning about. In this case we can inspect the contents from disk any time, so perhaps doing it before we install ruby would be good because we use bundle platform --update call to determine their ruby version, and that can fail if they're using a mangled binstub.