Feature #20275: Avoid extra backtrace entries for rescue and ensure

• Status: Closed
• Assignee: Eregon (Benoit Daloze)
• Target version: 3.4

[Eregon (Benoit Daloze)]

From https://bugs.ruby-lang.org/issues/19117#note-48:

def raise_nested_exceptions
  raise "First error"
rescue
  begin
    raise "Second error"
  rescue
    raise "Third error"
  end
end

raise_nested_exceptions

Current:

-:7:in 'Object#raise_nested_exceptions': Third error (RuntimeError)
	from -:4:in 'Object#raise_nested_exceptions'
	from -:1:in 'Object#raise_nested_exceptions'
	from -:11:in '<main>'
-:5:in 'Object#raise_nested_exceptions': Second error (RuntimeError)
	from -:1:in 'Object#raise_nested_exceptions'
	from -:11:in '<main>'
-:2:in 'Object#raise_nested_exceptions': First error (RuntimeError)
	from -:11:in '<main>'

The above repeated backtrace entries for Object#raise_nested_exceptions are because of CRuby implementation details.
It seems best to hide them because they do not help understanding the program, and semantically there is no (method or proc) call on line 1 or 4.

Proposed:

-:7:in 'Object#raise_nested_exceptions': Third error (RuntimeError)
	from -:11:in '<main>'
-:5:in 'Object#raise_nested_exceptions': Second error (RuntimeError)
	from -:11:in '<main>'
-:2:in 'Object#raise_nested_exceptions': First error (RuntimeError)
	from -:11:in '<main>'

We can see TruffleRuby and JRuby already behave this way, most likely because they do not use an extra frame for rescue.
It is definitely useful to have the same backtrace on different Ruby implementations as some tests rely on this.

TruffleRuby 23.1.2:

-:7:in `raise_nested_exceptions': Third error (RuntimeError)
	from -:11:in `<main>'
-:5:in `raise_nested_exceptions': Second error (RuntimeError)
	from -:11:in `<main>'
-:2:in `raise_nested_exceptions': First error (RuntimeError)
	from -:11:in `<main>'

JRuby 9.4.5.0:

RuntimeError: Third error
  raise_nested_exceptions at -:7
                   <main> at -:11
RuntimeError: Second error
  raise_nested_exceptions at -:5
                   <main> at -:11
RuntimeError: First error
  raise_nested_exceptions at -:2
                   <main> at -:11

[Eregon (Benoit Daloze)]

• Related to Feature #19117: Include the method owner in backtraces, not just the method name added

[Eregon (Benoit Daloze)]

Same thing for ensure:

begin
  raise
ensure
  p caller(0)
end

On CRuby master:

["-:4:in '<main>'", "-:4:in '<main>'"]

On CRuby 3.2:

["-:4:in `ensure in <main>'", "-:4:in `<main>'"]

Proposed:

["-:4:in '<main>'"]

Already the case on TruffleRuby and JRuby (except the quotes which have not changed yet of course):

["-:4:in `<main>'"]

[Eregon (Benoit Daloze)]

• Description updated (diff)

[mame (Yusuke Endoh)]

• Assignee set to ko1 (Koichi Sasada)

[Eregon (Benoit Daloze)]

• Description updated (diff)

[ko1 (Koichi Sasada)]

• Assignee changed from ko1 (Koichi Sasada) to matz (Yukihiro Matsumoto)

I don't have any opinion so I leave it on Matz.

[matz (Yukihiro Matsumoto)]

I agree with removing ensure in and rescue in entries from backtraces.

Matz.

[headius (Charles Nutter)]

JRuby also does not have a separate frame for rescues and ensures and we support removing these entries from backtraces.

[mame (Yusuke Endoh)]

I am in favor of this change, but I do not plan to write a patch and estimate its impact. Someone who wants this, please do it.
I recommend doing this earlier. Since it is incompatible, it may be too late closer to the upcoming release.

[Eregon (Benoit Daloze)]

• Assignee changed from matz (Yukihiro Matsumoto) to Eregon (Benoit Daloze)

PR: https://github.com/ruby/ruby/pull/10325

[Eregon (Benoit Daloze)]

• Status changed from Open to Closed

Applied in changeset git|74995a1a772903c5247886da1105caa27a4afa2d.

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[Feature #20275] Remove extra backtrace entries for rescue and ensure

[Eregon (Benoit Daloze)]

• Target version set to 3.4