Unexpected child debugging session when starting remote debuggee with `RUBYOPT=-rdebug/*`

[st0012]

Describe the bug

Some criteria for this issue:

1. Use RUBYOPT=-rdebug/open to load the debugger in remote mode.
2. The program runs another Ruby process like system("bundle exec rake")

When the above happens at the same time, it'll trigger double debugging sessions. I recorded a video to demo this:

2022-06-26.12.27.14.mov

This is annoying because the second session starts independently and hangs the program, until we connect to and disable it.

And this can happens to Rails apps.

I'm not sure it's at fault of the debugger as that's how ENV vars are passed to child processes. But perhaps we can do something from the debugger to prevent it?

To Reproduce

bar.rb

puts "bar"

target.rb

result = `ruby bar.rb`

puts(result)

terminal1

RUBYOPT=-rdebug/open ruby -Ilib target.rb

terminal2

rdbg -A

Expected behavior

The second process shouldn't start a debugging session.

[ko1]

Okay. Restore RUBYOPT while requiring session.rb.

[st0012]

@ko1 Thanks for the fix. But I just tested the PR but it doesn't solve the example I mentioned here, as it's not passed by the rdbg binary. Do you think there's a way to solve that case too?

[ko1]

Ah, I see. On this case, we can't recognize it should be kept or not.

Another idea is set RUBY_DEBUG_ENABLE=0 at session.rb and child processes can not load debug.rb, but it also prohibits invoking debugger if it is needed.

Another idea is removing -r debug/... but I'm afraid it can be done correctly.

[ko1]

My patch added RUBY_DEBUG_ADDED_RUBYOPT environment variable and

RUBY_DEBUG_ADDED_RUBYOPT='-r debug/open' RUBYOPT='-r debug/open' ruby ... will solve the issue. I think it is good workaround.

[st0012]

@ko1 I see, thank you.