From: merch-redmine@...
Date: 2021-03-01T23:54:12+00:00
Subject: [ruby-core:102685] [Ruby master Bug#11335] `ruby -r debug`	catchpoint problem

Issue #11335 has been updated by jeremyevans0 (Jeremy Evans).


I was able to reproduce this issue and confirm that the catch support is broken and has been broken since Ruby 2.0, since the raise event for set_trace_func is not triggered until after `$!` has been reset:

```
$ cat t/t13.rb
  set_trace_func proc { |*args|
    p $! if args.first == "raise"
  }

raise 'foo'

$ ruby19 -v t/t13.rb
ruby 1.9.3p551 (2014-11-13 revision 48407) [x86_64-openbsd]
#<RuntimeError: foo>
t/t13.rb:5:in `<main>': foo (RuntimeError)

$ ruby20 -v t/t13.rb
ruby 2.0.0p648 (2015-12-16 revision 53162) [x86_64-openbsd]
nil
t/t13.rb:5:in `<main>': foo (RuntimeError)
```

Rewriting debug using tracepoint is one option, but I suspect most people would use an alternative debugger such as byebug, so I'm not sure it is worth the effort to switch.  Maybe it is just time to retire debug?

----------------------------------------
Bug #11335: `ruby -r debug` catchpoint problem
https://bugs.ruby-lang.org/issues/11335#change-90680

* Author: sigsys (Math Ieu)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.1.6p336 (2015-04-13 revision 50298) [i386-freebsd10]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
With a `test-debug.rb` like this:

~~~
raise 'test'
~~~

And starting the debugger like this:

~~~
ruby -r debug test-debug.rb
~~~

By default, the catchpoint is `StandardError`, but it doesn't work:

~~~
test-debug.rb:1:raise 'test'
(rdb:1) catch
Catchpoint StandardError.
(rdb:1) c
test-debug.rb:1:in `<main>': test (RuntimeError)
~~~

And the debugger exits without catching the exception.

But, by setting the catchpoint to `NilClass` (or one of its ancestors), then it works:

~~~
test-debug.rb:1:raise "test"
(rdb:1) catch NilClass
Set catchpoint NilClass.
(rdb:1) c
test-debug.rb:1: `' (NilClass)
        from test-debug.rb:1:in `<main>'
test-debug.rb:1:raise "test"
~~~

And the debugger does not exit and allows further debugging.

By looking at `lib/debug.rb`, it looks like that the `set_trace_func` callback it sets assumes that `$!` will be set to the exception to be raised when a `'raise'` event occurs.  But it is not the case, `$!` seems to always be `nil`.




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