[ruby-core:107356] [Ruby master Bug#18458] Segmentation fault when missing Warning#warn method

Issue #18458 has been updated by naruse (Yui NARUSE).

Backport changed from 2.6: DONTNEED, 2.7: DONTNEED, 3.0: REQUIRED, 3.1: REQUIRED to 2.6: DONTNEED, 2.7: DONTNEED, 3.0: REQUIRED, 3.1: DONE

ruby_3_1 d3a2a3c5420fecfee54cbf3fbdd9287bc6c58f03 merged revision(s) 9e0a91d0640600f2dfd7fc1d5fae6667019c9ca5.

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Bug #18458: Segmentation fault when missing Warning#warn method
https://bugs.ruby-lang.org/issues/18458#change-96257

* Author: etienne (テ液ienne Barriテゥ)
* Status: Closed
* Priority: Normal
* ruby -v: 3.1.0p0
* Backport: 2.6: DONTNEED, 2.7: DONTNEED, 3.0: REQUIRED, 3.1: DONE
----------------------------------------
If you remove the `Warning#warn` method and call `Kernel#warn`, you get a segmentation fault:

ruby 3.1.0:
``` 
$ ruby -e 'Warning.undef_method(:warn); warn ""' 2>&1 | head -2                                                                                                                                                                                                                    
<internal:warning>:51: [BUG] Segmentation fault at 0x0000000000000010
ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [x86_64-darwin21]
```

It's not new, you get the same with 3.0.3:
```
$ ruby -e 'Warning.undef_method(:warn); warn ""' 2>&1 | head -2                                                                                                                                                                                                                    
<internal:warning>:51: [BUG] Segmentation fault at 0x0000000000000010
ruby 3.0.3p157 (2021-11-24 revision 3fb7d2cadc) [x86_64-darwin20]
```

In 2.7 though you get a NoMethodError exception:
```
$ ruby --disable-all -e 'Warning.undef_method(:warn); warn ""'
Traceback (most recent call last):
	1: from -e:1:in `<main>'
<internal:warning>:43:in `warn': undefined method `warn' for Warning:Module (NoMethodError)
```

(I disabled gems because rubygems core extensions adds two lines of backtrace, but it's the same result in the end)



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