From: "AMomchilov (Alexander Momchilov) via ruby-core" <ruby-core@...>
Date: 2023-02-13T15:49:49+00:00
Subject: [ruby-core:112411] [Ruby master Feature#19197] Add Exception#root_cause

Issue #19197 has been updated by AMomchilov (Alexander Momchilov).


Hey Robert, thanks for taking the time to write.

rubyFeedback (robert heiler) wrote in #note-2:
> but on the issue of object.cause.cause.cause
> (object.method1.method1.method1). From an API point of view
> I think this is normally not "the ruby way" when it leads
> to repetition.

Ah, I wasn't suggesting to use this style of code, it was just a very simple/concise demonstration of the structure of the sample exception I made. I've updated my post to clarify that.

rubyFeedback (robert heiler) wrote in #note-2:
> If I understand it correctly you prefer more control over
> the error report?

Correct!

rubyFeedback (robert heiler) wrote in #note-2:
> If so then I think that makes sense; mame
> improved on the error feedback ruby gives, if I recall 
> correctly. I now get a lot more information about where an
> error happens, including a follow-up trace. I don't remember
> this in the ruby 1.8.x era, for instance.

Sorry, I don't understand what you're trying to say here

----------------------------------------
Feature #19197: Add Exception#root_cause
https://bugs.ruby-lang.org/issues/19197#change-101853

* Author: AMomchilov (Alexander Momchilov)
* Status: Open
* Priority: Normal
----------------------------------------
### Description

I would like to add a `#root_cause` method to `Exception`.

It returns the last exception in linked-list of causality chain, that is, the original exception (whose own `cause` is `nil`).

### Example

```ruby
e = begin
    raise 'A' # This is the root cause
  rescue => a
    begin
      raise 'B'
    rescue => B
      begin
        raise 'C' # This is the outermost cause assigned to `e`
      rescue => c
        c
      end
    end
  end

# Here's what the structure looks like:
# C -> B -> A -> nil  
p(e)                   # => #<RuntimeError: C>
p(e.cause)             # => #<RuntimeError: B>
p(e.cause.cause)       # => #<RuntimeError: A>
p(e.cause.cause.cause) # => nil

# Here's the proposed API, showing that A is the root cause of e
p(e.root_cause)        # => #<RuntimeError: A>
# And that the root_cause has no further cause
p(e.root_cause.cause)  # => nil
```

### Motivation

There are some kinds of exceptions that can occur all over the place (and might be wrapped by arbitrarily many middlemen), but are attributable to a singular global cause. For example, a database outage could raise exceptions in almost every line of business logic of an app that uses ActiveRecord models.

Fundamentally, you wouldn't want an error report for every one of these lines. You'd want to look at the root cause, and bucket all SQL-connection issues into a single report, regardless of where they surface.

### Implementation

Draft PR: https://github.com/ruby/ruby/pull/6913



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