From: "AMomchilov (Alexander Momchilov) via ruby-core" <ruby-core@...>
Date: 2023-02-13T15:56:01+00:00
Subject: [ruby-core:112412] [Ruby master Feature#19197] Add Exception#root_cause

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





Eregon (Benoit Daloze) wrote in #note-3:

> I think this makes sense and it's pretty trivial.

> I think you need to add this to a dev meeting ticket so it will be decided whether it's accepted or not.



Hey Benoit!



What's a "dev meeting ticket"?



Also, what do you think of some alternative spellings, like having a `#causes: Array[Exception]`, on which you could just call `#last`?



E.g.



```ruby

p e.causes.last # The root cause

```



Alternatively, you could do this song-dance:



```ruby

p Enumerator.produce(e) { |e| e.cause or raise StopIteration }.to_a.last

```



Interestingly, there's `Enumerable#first`, but not `Enumerable#last`, so you have to go through `#to_a` (since there is a `Array#last`). Perhaps that should be its own pitch ����



----------------------------------------

Feature #19197: Add Exception#root_cause

https://bugs.ruby-lang.org/issues/19197#change-101854



* 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







-- 

https://bugs.ruby-lang.org/

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