[ruby-core:105418] [Ruby master Bug#18170] Exception#inspect should not include newlines

Issue #18170 has been updated by mame (Yusuke Endoh).


Eregon (Benoit Daloze) wrote in #note-4:
> The quotes around the message feel redundant to me and likely to cause much more incompatibility.

Because we don't inspect an exception object so often, I think the redundancy is not much of a problem. I somewhat agree with the concern about incompatibility. Though it is not very admirable to depend on the return value of `#inspect`, some changes of tests are actually needed for my PR.

> I'm neutral regarding escaping \n and non-printable characters.

I think of three options.

1. No change
2. Apply String#inspect to the message (as my PR does)
3. Apply String#inspect to the message, and drop the first and last quotes from the returned string

(3) is very ad-hoc but maybe will work well in many cases.

----------------------------------------
Bug #18170: Exception#inspect should not include newlines
https://bugs.ruby-lang.org/issues/18170#change-93837

* Author: mame (Yusuke Endoh)
* Status: Assigned
* Priority: Normal
* Assignee: mame (Yusuke Endoh)
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
Is this intentional?

```
p StandardError.new("foo\nbar")
#=>
# #<StandardError: foo
# bar>
```

I expect `#inspect` returns a one-line string. How about returning `#<StandardError: "foo\nbar">` or something?

Recently, multi-line error messages have been increasing by the introduction of did_you_mean and error_highlight. Printing an object that contains such an exception leads to a tricky output:

```
class Foo
  def initialize
    @exception = begin; exampl; rescue Exception; $!; end
  end

  def example
  end
end

p Foo.new
#=>
# #<Foo:0x00007f15aeb4ba48 @exception=#<NameError: undefined local variable or method `exampl' for #<Foo:0x00007f15aeb4ba48 ...>
#
#     @exception = begin; exampl; rescue Exception; $!; end
#                         ^^^^^^
# Did you mean?  example>>
```

This issue was originally found by @ioquatix 



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