rdbg doesn't respect the bundler/setup loaded by bundler

[st0012]

Your environment

• ruby -v: 3.1
• rdbg -v: 1.6.1

Describe the bug

When running bundle exec, bundler will inject something like -r path_to_bundler/setup into the RUBYOPT environment variable. And that's how it makes sure every gem loaded afterward is at the version specified in the Gemfile.lock.

But currently, the rdbg executable aren't passing this info correctly.

debug/exe/rdbg

Lines 16 to 21 in 390b764

	env = ::DEBUGGER__::Config.config_to_env_hash(config)
	rubyopt = env['RUBYOPT']
	env['RUBY_DEBUG_ADDED_RUBYOPT'] = added = "-r #{libpath}/#{start_mode}"
	env['RUBYOPT'] = "#{added} #{rubyopt}"
	exec(env, cmd, *ARGV)

This code has 2 problems:

1. rubyopt = env['RUBYOPT'] should be rubyopt = ENV['RUBYOPT'] because env is a hash produced with the debugger configurations instead of the current environment. So currently the env['RUBYOPT'] is always nil.
2. "#{added} #{rubyopt}" should be #{rubyopt} "#{added} instead to honor the requiring order.
   • -rbundler/setup -rdebug/start instead of -rdebug/start -rbundler/setup because the later will cause the debugger not to load the dependency specified in Gemfile.

To Reproduce

This problem doesn't always cause real issues though. Errors only happen when all these conditions are fulfilled:

1. There's a library used by both the debugger and the user's program, e.g. timeout (used by reline, which is used by the debugger)
2. The system has at least 2 versions of the gem (e.g. 0.2.0 and 0.3.0)
3. The user program uses the older version (e.g. 0.2.0)

Then rdbg -c -- <user program> will trigger this error:

You have already activated timeout 0.3.0, but your Gemfile requires timeout 0.2.0. Prepending `bundle exec` to your command may solve this. (Gem::LoadError)

The real program though, is that appending bundle exec before rdbg won't fix the problem as it should due to the described reason.

Expected behavior

bundle exec rdbg # ... should avoid the Gem::LoadError.