[ruby-core:106229] [Ruby master Feature#18296] Custom exception formatting should override `Exception#full_message`.

Issue #18296 has been updated by Dan0042 (Daniel DeLorme).


From what I understand, one motivation of this proposal is to have the "did you mean" be part of #full_message but not #message or #inspect. So if we have `putz rescue p($!)` then

```
==current==
#<NameError: undefined local variable or method `putz' for main:Object
Did you mean?  putc
               puts>

==with #18170==
#<NameError:"undefined local variable or method `putz' for main:Object\nDid you mean?  putc\n               puts">

==desired==
#<NameError: undefined local variable or method `putz' for main:Object>
```

Did I understand correctly?


----------------------------------------
Feature #18296: Custom exception formatting should override `Exception#full_message`.
https://bugs.ruby-lang.org/issues/18296#change-94840

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
----------------------------------------
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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