[ruby-core:97104] [Ruby master Bug#16618] Rescue called twice when raise in ensure

Issue #16618 has been reported by davidsiaw (David Siaw).

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Bug #16618: Rescue called twice when raise in ensure
https://bugs.ruby-lang.org/issues/16618

* Author: davidsiaw (David Siaw)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-linux-musl]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
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Under very specific circumstances (a `return` with code after it), a `raise` in an `ensure` block causes the `ensure` block to be called twice after rescuing in a `rescue` block above it.

Here is a very small reproduction case:

```ruby
class ABC < StandardError; end

def meow
  return
  puts 'a'
rescue ABC
  puts 'rescue'
ensure
  puts 'ensure'
  raise ABC
end

meow
```

Causes the output 

```
ensure
rescue
ensure
Traceback (most recent call last):
	1: from spec/meow.rb:13:in `<main>'
spec/meow.rb:10:in `meow': ABC (ABC)
```

However, if I remove the code below the `return`, the behavior is more reasonable:

```ruby
class ABC < StandardError; end

def meow
  return
rescue ABC
  puts 'rescue'
ensure
  puts 'ensure'
  raise ABC
end

meow
```

```
ensure
Traceback (most recent call last):
	1: from spec/meow.rb:14:in `<main>'
spec/meow.rb:9:in `meow': ABC (ABC)
```

It does not seem to matter what code comes after `return`. It also does not seem to matter what code comes before the `return`, as long as the `return` is run. It could throw errors or it might not, but there seems to be a definite requirement that there is code after the `return` for this bug to occur.

Possibly related to #13930? I am not sure.



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