[ruby-core:117366] [Ruby master Bug#20400] Nested BEGIN{} execution order

28 Mar 2024

      Issue #20400 has been reported by kddnewton (Kevin Newton).

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Bug #20400: Nested BEGIN{} execution order
https://bugs.ruby-lang.org/issues/20400

* Author: kddnewton (Kevin Newton)
* Status: Open
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
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Right now there are specs for the order in which `BEGIN{}` should be executed, which is the order they appear in the file. For example:

```ruby
BEGIN { print "1" }
print "4"
BEGIN { print "2" }
print "5"
BEGIN { print "3" }
```

should output "12345". However, I couldn't find any tests/specs on what happens when `BEGIN{}` is nested. The order appears to be somewhat confusing, so I wanted to clarify if it was intentional or a bug. For example:

```ruby
BEGIN {
  print "1"
  BEGIN { print "2" }
}
```

prints "21", and:

```ruby
BEGIN {
  print "1"
  BEGIN { print "2" }
  BEGIN { print "3" }
}
```

prints "231", and finally:

```ruby
BEGIN {
  print "1"
  BEGIN {
    print "2"
    BEGIN { print "3" }
  }
  BEGIN { print "4" }
}
```

prints "3241". Is this intentional?

-- 
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