[ruby-core:105036] [Ruby master Feature#18083] Capture error in ensure block.

Issue #18083 has been updated by ioquatix (Samuel Williams).


> A few places, but in relative usages probably 1/1000 of begin/rescue or ensure/end patterns, right?

I scanned top 10,000 gems by download count:

Checking for "$!":
Found 459 gems with this pattern.
Found 2624 instances of the pattern.

Checking for "ensure":
Found 3221 gems with this pattern.
Found 28306 instances of the pattern.

Checking for /(.*ensure(.*\n){0,4}.*\$!.*)/:
Found 35 gems with potential issues.
Found 46 instances of the pattern.

Any usage of $! is potentially suspect, but at least 35 gems out of 10,000 are definitely incorrect.

----------------------------------------
Feature #18083: Capture error in ensure block.
https://bugs.ruby-lang.org/issues/18083#change-93445

* 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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