From: "mame (Yusuke Endoh)" <noreply@...>
Date: 2021-11-11T14:06:45+00:00
Subject: [ruby-core:106030] [Ruby master Bug#18296] Custom exception formatting should override `Exception#full_message`.

Issue #18296 has been updated by mame (Yusuke Endoh).


Eregon (Benoit Daloze) wrote in #note-7:
> mame (Yusuke Endoh) wrote in #note-6:
> > Does this proposal include that the ruby interpreter should use `#full_message` to show the error information? This is an incompatibility, is it acceptable?
> 
> Yes, let's fix that.

Thanks. I think that this is the most important part of this proposal. It should be clearly explained in the description. Actually, I don't think that the implementation of error_highlight and did_you_mean is so important.

I have no strong opinion, but if the change is accepted, I will be happy to change the implementation of error_highlight.

Also, the motivation of this proposal is not clear to me. The implementation of error_highlight and did_you_mean is indeed dirty, but I don't see how it matters to end users. I guess it may matter when a user calls `Exception#message`, but anyway, it should also be clearly explained the description.

@eregon changed the code snippet in the description, which made the proposal clear to me. However, in regard to the backtrace, eregon's proof-of-concept looks much more difficult than the code in the original description. I believe that it would be good to implement it and to confirm that the proposal actually works before the discussion.

Because this ticket started with unclear description, and the discussion so far is also unclear. How about closing this ticket and creating a new ticket with a clear explanation of the motivation, the proposal, and a proof-of-concept patch if any?

----------------------------------------
Bug #18296: Custom exception formatting should override `Exception#full_message`.
https://bugs.ruby-lang.org/issues/18296#change-94620

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
After discussing with @eregon, we came to the conclusion that the current implementation of `did_you_mean` and `error_highlight` could avoid many issues by using `Exception#full_message`.

We propose to introduce a more nuanced interface:

```ruby
class Exception
  def full_message(highlight: bool, order: [:top or :bottom], **options)
    # ...
  end
end

module DidYouMean
  module Formatter
    def full_message(highlight:, did_you_mean: true, **options)
      buffer = super(highlight: highlight, **options).dup
      buffer << "extra stuff"
    end
  end
end
Exception.prepend DidYouMean::Formatter

module ErrorHighlight
  module Formatter
    def full_message(highlight:, error_highlight: true, **options)
      # same as above
    end
  end
end
Exception.prepend ErrorHighlight::Formatter
```



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