[ruby-core:106021] [Ruby master Bug#18296] Custom exception formatting should override `Exception#full_message`.

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


TBH I'm unsure if I could understand what you propose. It would be very helpful if you could create a proof-of-concept patch.

I have one concern. My minimum expectation of error_highlight and did_you_mean is that the ruby interpreter should print their hints by default. However, at the present time, the ruby interpreter uses `#message` instead of `#full_message` to show the error information of uncaught exception.

```
$ ruby -e 'class Foo < Exception; def message = "message"; def full_message = "full_message"; end; raise Foo.new'
-e:1:in `<main>': message (Foo)
```

Does this proposal include that the ruby interpreter should use `#full_message` to show the error information? This is an incompatibility, is it acceptable?

There is an ecosystem to handle uncaught exception, including application monitoring services (Newrelic, DataDog, ScoutAPM, ...) and Rails' exception handling system for development mode. They also should change their code base to use `#full_message` (or more dedicated display depending on their context). I think we need to coordinate them if we introduce this incompatibility. cc @ivoanjo

----------------------------------------
Bug #18296: Custom exception formatting should override `Exception#full_message`.
https://bugs.ruby-lang.org/issues/18296#change-94607

* 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_highlighter` 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
  class Formatter
    def full_message(highlight:, did_you_mean: true, **options)
      buffer = super(highlight: highlight, **options).dup
      buffer << "extra stuff"
    end
  end
end

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



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