From: tagomoris@...
Date: 2018-06-08T08:58:28+00:00
Subject: [ruby-core:87454] [Ruby trunk Bug#14835] Impossible to know whether an exception was rescued or not using TracePoint

Issue #14835 has been reported by tagomoris (Satoshi TAGOMORI).

----------------------------------------
Bug #14835: Impossible to know whether an exception was rescued or not using TracePoint
https://bugs.ruby-lang.org/issues/14835

* Author: tagomoris (Satoshi TAGOMORI)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.6.0preview2 (2018-05-31 trunk 63539) [x86_64-darwin17]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
TracePoint supports :raise and :return events, and :return event will be invoked when an exception occurs in a method.
But its TracePoint block parameter instance doesn't have any information about raised exceptions.

That means, we can know an exception was raised in a method, but we cannot know an exception was rescued or not there.

```ruby
def thrower
  raise "exception"
end

def caller_without_rescue
  thrower
end

tp = TracePoint.trace(:raise, :return) do |tp|
  case tp.event
  when :raise
    p(here: "trace", event: :raise, klass: tp.defined_class, method: tp.method_id, exception: tp.raised_exception)
  else
    p(here: "trace", event: tp.event, klass: tp.defined_class, method: tp.method_id, value: tp.return_value)
  end
end


caller_with_rescue

puts "\n----------------------\n"

begin
  caller_without_rescue
rescue => e2
  puts "outer rescue: #{e2}"
end
```

The script above shows these events, but TracePoint events are completely same in these two examples.

```
# caller_with_rescue
{:here=>"trace", :event=>:raise, :klass=>Object, :method=>:thrower, :exception=>#<RuntimeError: exception>}
{:here=>"trace", :event=>:return, :klass=>Object, :method=>:thrower, :value=>nil}
rescue: exception
{:here=>"trace", :event=>:return, :klass=>Object, :method=>:caller_with_rescue, :value=>nil}

----------------------
# caller_without_rescue
{:here=>"trace", :event=>:raise, :klass=>Object, :method=>:thrower, :exception=>#<RuntimeError: exception>}
{:here=>"trace", :event=>:return, :klass=>Object, :method=>:thrower, :value=>nil}
{:here=>"trace", :event=>:return, :klass=>Object, :method=>:caller_without_rescue, :value=>nil}
outer rescue: exception
```

My expectation is that TracePoint instance should contain exception instance in `raised_exception` at the time when it's not rescued.




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