[ruby-core:106003] [Ruby master Bug#18170] Exception#inspect should not include newlines

Issue #18170 has been updated by Eregon (Benoit Daloze).


I've been thinking about this again, and I'm not sure if
```
#<Foo:0x00007f15aeb4ba48 @exception=#<NameError: undefined local variable or method `exampl' for #<Foo:0x00007f15aeb4ba48 ...>
    @exception = begin; exampl; rescue Exception; $!; end
                        ^^^^^^
Did you mean?  example>>
```
or
```
#<Foo:0x00007f15aeb4ba48 @exception=#<NameError: "undefined local variable or method `exampl' for #<Foo:0x00007f15aeb4ba48 ...>\n    @exception = begin; exampl; rescue Exception; $!; end\n                        ^^^^^^\nDid you mean?  example">>
```
is better.
The object's inspect is unreadable in both cases anyway.

For readability of the error, I believe the first is better.
And if the error was shown alone (common case, e.g. if an exception is shown in IRB or with `p exception`), the first is clearly much better:
```
#<NameError: undefined local variable or method `exampl' for #<Foo:0x00007f15aeb4ba48 ...>
    @exception = begin; exampl; rescue Exception; $!; end
                        ^^^^^^
Did you mean?  example>
```
vs
```
#<NameError: "undefined local variable or method `exampl' for #<Foo:0x00007f15aeb4ba48 ...>\n    @exception = begin; exampl; rescue Exception; $!; end\n                        ^^^^^^\nDid you mean?  example>
```
(that's completely unreadable)

I think needing to read the `inspect` of an object containing an exception is pretty rare, and not worth making `Exception#inspect` less readable (which can be very useful for debugging).
And there is an easy workaround, that object storing an exception can have a custom #inspect and something like:
```
#<ExceptionWrapper:0x00007f15aeb4ba48 for NameError with message:
undefined local variable or method `exampl' for #<Foo:0x00007f15aeb4ba48 ...>
    @exception = begin; exampl; rescue Exception; $!; end
                        ^^^^^^
Did you mean?  example>
```
That's readable.

There might also be the need to disable did_you_mean and error_highlight for a given exception, I think that's a reasonable request, but also a different feature.
Maybe having something like `Exception#original_message` seems a simple way to do that (the message, unaffected by did_you_mean/error_highlight/etc).
Or have Exception#message assemble different parts of the exception, and did_you_mean/error_highlight would use a proper hook to add extra data. Then Exception#message could accept some argument whether you want the extra data or not, or just a single line, etc.

----------------------------------------
Bug #18170: Exception#inspect should not include newlines
https://bugs.ruby-lang.org/issues/18170#change-94551

* 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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