[ruby-core:115752] [Ruby master Feature#18083] Capture error in ensure block.

15 Dec 2023

      Issue #18083 has been updated by Dan0042 (Daniel DeLorme).

ko1 (Koichi Sasada) wrote in #note-20:
...
my proposal is introducing dynamic scope, not syntactical scope like:
I think this is a good idea, definitely an improvement over the current situation. `$!` is already always correct inside a `rescue` clause, and that would make it always correct inside the `ensure` clause. But I want to confirm if this would be the expected behavior:

```ruby
#1
p $! #=> A
begin
  # no raise
ensure
  p $! #=> nil (unlike A currently)
end
p $! #=> A (restored after previous begin-ensure block?)

#2
p $! #=> A
begin
  raise "B"
rescue 
  p $! #=> B
  #not re-raised
ensure
  p $! #=> B (unlike A currently)
end
p $! #=> A (restored after previous begin-ensure block?)
```

----------------------------------------
Feature #18083: Capture error in ensure block.
https://bugs.ruby-lang.org/issues/18083#change-105683

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
----------------------------------------
As discussed in https://bugs.ruby-lang.org/issues/15567 there are some tricky edge cases.

As a general model, something like the following would be incredibly useful:

``` ruby
begin
 ...
ensure => error
  pp "error occurred" if error
end
```

Currently you can get similar behaviour like this:

``` ruby
begin
  ...
rescue Exception => error
  raise
ensure
  pp "error occurred" if error
end
```

The limitation of this approach is it only works if you don't need any other `rescue` clause. Otherwise, it may not work as expected or require extra care. Also, Rubocop will complain about it.

Using `$!` can be buggy if you call some method from `rescue` or `ensure` clause, since it would be set already. It was discussed extensively in https://bugs.ruby-lang.org/issues/15567 if you want more details.

-- 
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