[ruby-core:84583] [Ruby trunk Bug#14267] Lazy proc allocation introduced in #14045 creates regression

Issue #14267 has been reported by myronmarston (Myron Marston).

----------------------------------------
Bug #14267: Lazy proc allocation introduced in #14045 creates regression
https://bugs.ruby-lang.org/issues/14267

* Author: myronmarston (Myron Marston)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-darwin15]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
The following script consistently prints `Proc equality: true` on versions of Ruby before 2.5, but prints `Proc equality: false` on Ruby 2.5:

``` ruby
# regression.rb
def return_proc(&block)
  block
end

def return_procs(&block)
  block.inspect if ENV['INSPECT_BLOCK']

  proc_1 = return_proc(&block)
  proc_2 = return_proc(&block)

  return proc_1, proc_2
end

proc_1, proc_2 = return_procs { }

puts RUBY_VERSION
puts "Proc equality: #{proc_1 == proc_2}"
```

Here's the output on Ruby 2.4 and 2.5:

```
$ chruby 2.4
$ ruby regression.rb
2.4.2
Proc equality: true
$ chruby 2.5
$ ruby regression.rb
2.5.0
Proc equality: false
```

As the output shows, the two procs were equal on 2.4 but are no longer equal on 2.5.  I believe this is due to the lazy proc allocation introduced in #14045.  Note that if I call a method on the proc (such as `inspect`) it defeats the lazy allocation and "fixes" the regression:

```
$ chruby 2.5
$ INSPECT_BLOCK=1 ruby regression.rb
2.5.0
Proc equality: true
```

This caused a bug in RSpec, which I've [worked around for now](https://github.com/rspec/rspec-core/commit/84670489bb4943a62e783bd65f96e4b55360b141) by calling `__id__` on the proc.

Is there a way to keep the lazy proc allocation while fixing this regression?



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