Bug #20253: `Proc.dup` and `Proc#clone` don't preserve finalizers

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 3.0: WONTFIX, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN

[byroot (Jean Boussier)]

While reviewing the fix for [Bug #20250] @peterzhu2118 (Peter Zhu) pointed that FL_FINALIZE should probably also be cleared.

However after some extra testing, it appears Object#dup and Object#clone do copy over the finalizer (which makes sense).

But for some reason Proc has its own dup/clone implementation, which does copy the FL_FINALIZE flag, but doesn't copy the finalizer:

Test script:

def fin(sym)
  ->(_) { p sym }
end

obj = Object.new
ObjectSpace.define_finalizer(obj, fin(:obj))
obj.dup
obj.clone

proc = Proc.new { }
ObjectSpace.define_finalizer(proc, fin(:proc))
proc.dup
proc.clone

Expected output:

:proc
:proc
:proc
:obj
:obj
:obj

Actual output:

:proc
:obj
:obj
:obj

This discrepancy is present all the way back to Ruby 1.9.

It's so niche I'm not sure it's worth a backport though...

[byroot (Jean Boussier)]

• Related to Bug #20250: Crash with "Object ID seen, but not in mapping table: proc" error added

[byroot (Jean Boussier)]

While looking at this, it appears that instance variables are also not copied over in Proc#dup, but somehow are in Proc#clone:

def ivar_dup(obj)
  obj.instance_variable_set(:@foo, 1)
  p [:dup, obj.dup.instance_variable_get(:@foo)]
  p [:clone, obj.clone.instance_variable_get(:@foo)]
end

ivar_dup(Object.new)
ivar_dup(Proc.new { })

[:dup, 1]
[:clone, 1]
[:dup, nil]
[:clone, 1]

Which really raise the question of why Proc has a completely different codepath for duping/cloning, AFAIK no other core type does this.

[byroot (Jean Boussier)]

We just found yet another issue with @etienne (Étienne Barrié):

>> Proc.new { }.freeze.clone
(irb):1:in `initialize_copy': can't modify frozen Proc: #<Proc:0x000000011e3a96b0 (irb):1> (FrozenError)
	from (irb):1:in `initialize_clone'
	from (irb):1:in `clone'
	from (irb):1:in `<main>'

This one was introduced in Ruby 3.3.0.

[byroot (Jean Boussier)]

https://github.com/ruby/ruby/pull/9926 fixes all the issues above and a few others.

[byroot (Jean Boussier)]

• Status changed from Open to Closed

Applied in changeset git|de1a586ecc2ee7f465f0c0a69291054136a3a819.

---

proc.c: get rid of CLONESETUP

[Bug #20253]

All the way down to Ruby 1.9, Proc, Method, UnboundMethod
and Binding always had their own specific clone and dup routine.

This caused various discrepancies with how other objects behave
on dup and `clone. [Bug #20250], [Bug #20253].

This commit get rid of CLONESETUP and use the the same codepath
as all other types, so ensure consistency.

NB: It's still not accepting the freeze keyword argument on clone.

Co-Authored-By: Étienne Barrié [e-mail]