[ruby-core:91622] [Ruby trunk Bug#15622] Default version of Bundler incorrectly invoked when using binstubs

[richard.schneeman+ruby-lang@gmail.com]

Issue #15622 has been reported by schneems (Richard Schneeman).

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Bug #15622: Default version of Bundler incorrectly invoked when using binstubs 
https://bugs.ruby-lang.org/issues/15622

* Author: schneems (Richard Schneeman)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.6.1p33 (2019-01-30 revision 66950) [x86_64-linux]
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
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When trying to run a binstub with Ruby 2.6.1 with Bundler 2.0.1 on the system, the wrong version of Bundler gets loaded which then fails when the Gemfile.lock points to a 2.x version (since the default version that ships with Ruby is Bundler 1.x. While this was discovered on Heroku and is discussed in this issue https://github.com/heroku/heroku-buildpack-ruby/issues/856#issuecomment-467205932 I was able to replicate the problem fairly easily with docker. I've provided instructions below.

## Reproduction

Start a docker image with Ruby 2.6.1

```
docker run -it --rm ruby:2.6.1 bash
```

Install bundler, rails, make a new app, and remove the `begin/rescue/end` from the `bin/rake` binstub. To trigger the error run a `rake` command without `bundle exec`:

```
gem install bundler -v 2.0.1
gem install rails -v 6.0.0.beta1
rails new ruby-2-6-bundler-2-issue


cd ruby-2-6-bundler-2-issue

cat <<EOT > bin/rake
#!/usr/bin/env ruby
require_relative '../config/boot'
require 'rake'
Rake.application.run
EOT

rake -T
```

Output:

```
You must use Bundler 2 or greater with this lockfile.
```

Expected:

Bundler 2 is available on the system, and is the latest version, so it should be invoked instead of the default bundler version.





-- 
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