Bug #13043: Exception#cause can become recursive/infinite

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.3.3p222 (2016-11-21 revision 56859) [x86_64-darwin16]
• Backport: 2.1: WONTFIX, 2.2: WONTFIX, 2.3: REQUIRED

[ccutrer (Cody Cutrer)]

In a certain situation, Exception#cause can become an infinite list:

def raise_errors
  begin
    raise "error 1"
  ensure
     orig_error = $!
     begin
       raise "error 2"
     rescue => err
       raise orig_error || err
     end
  end
end

x = nil
begin
  raise_errors
rescue
  x = $!
end

x.cause.cause.object_id == x.object_id

Note that this pattern happened during an HTTP request with net/http: see https://github.com/ruby/ruby/blob/v2_3_1/lib/net/http/response.rb#L261. I would expect that x would be "error 2", x.cause would be "error 1", and x.cause.cause would be nil. Instead an infinite loop forms, breaking error reporting code that loops over an exception's cause

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)
• Backport changed from 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN to 2.1: REQUIRED, 2.2: REQUIRED, 2.3: REQUIRED

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset r57137.

---

eval.c: fix circular cause

• eval.c (exc_setup_cause): always set cause of cause to get rid
  of circular references. [ruby-core:78688] [Bug #13043]

[usa (Usaku NAKAMURA)]

• Backport changed from 2.1: REQUIRED, 2.2: REQUIRED, 2.3: REQUIRED to 2.1: REQUIRED, 2.2: DONE, 2.3: REQUIRED

ruby_2_2 r57222 merged revision(s) 57137.

[usa (Usaku NAKAMURA)]

• Backport changed from 2.1: REQUIRED, 2.2: DONE, 2.3: REQUIRED to 2.1: REQUIRED, 2.2: REQUIRED, 2.3: REQUIRED

... but reverted in ruby_2_2 because it causes SEGV.

[usa (Usaku NAKAMURA)]

• Backport changed from 2.1: REQUIRED, 2.2: REQUIRED, 2.3: REQUIRED to 2.1: REQUIRED, 2.2: DONE, 2.3: REQUIRED

ruby_2_2 r57229 merged revision(s) 57137.

[usa (Usaku NAKAMURA)]

• Backport changed from 2.1: REQUIRED, 2.2: DONE, 2.3: REQUIRED to 2.1: WONTFIX, 2.2: WONTFIX, 2.3: REQUIRED

I've finally gave up to backport this into ruby_2_2, because of a test of rake failed.
I doubt that the test is nonsense, but a maintenance branch should be conservative about changing its behavior.