[ruby-core:69878] [Ruby trunk - Bug #11335] [Open] `ruby -r debug` catchpoint problem

[ruby-core:69878] [Ruby trunk - Bug #11335] [Open] `ruby -r debug` catchpoint problem

[sigsys]

Issue #11335 has been reported by Math Ieu.

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

* Author: Math Ieu
* Status: Open
* Priority: Normal
* Assignee: 
* 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`.




-- 
https://bugs.ruby-lang.org/

[ruby-core:90360] [Ruby trunk Bug#11335] `ruby -r debug` catchpoint problem

[oleynikov]

Issue #11335 has been updated by oleynikov (Alexander Oleynikov).


I was able to reproduce the issue on newer Ruby.

```
$ ruby -v
ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-openbsd]
```

sigsys (Math Ieu) wrote:
> 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`.

Exactly. When `set_trace_func` handler proc gets executed with a `'raise'` event, the `$!` is still `nil`.
`DEBUGGER__::Context#excn_handle` wants to find a class of the raised exception in `$!`, but always finds `nil` there.

We could fix that by replacing `Kernel#set_trace_func` with `TracePoint`. It is the recommended way according to the docs, where `set_trace_func` since Ruby 2.1 contains a note, saying "this method is obsolete, please use TracePoint instead". Instead of `$!` we should use `TracePoint#raised_exception` to get correct results.

I'm a bit afraid to work on this issue myself, because I found no specs for the debugger and I can accidentally break something without noticing. But if nobody else is interested in doing this, I will try.

----------------------------------------
Bug #11335: `ruby -r debug` catchpoint problem
https://bugs.ruby-lang.org/issues/11335#change-75470

* Author: sigsys (Math Ieu)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* 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`.




-- 
https://bugs.ruby-lang.org/