From: mame@...
Date: 2020-12-17T02:39:34+00:00
Subject: [ruby-core:101485] [Ruby master Bug#17400] Incorrect character	downcase for Greek Sigma

Issue #17400 has been updated by mame (Yusuke Endoh).


Just FYI: I found the special handling code of Greek Sigma in v8. Looks like that it checks if the next character (if any) is a letter or not.

https://github.com/v8/v8/blob/4b9b23521e6fd42373ebbcb20ebe03bf445494f9/src/unicode.cc#L177-L185

It uses non-final lower sigma even if the next character is Japanese.

```
$ node
> "�����".toLowerCase()
'�����'
```

----------------------------------------
Bug #17400: Incorrect character downcase for Greek Sigma
https://bugs.ruby-lang.org/issues/17400#change-89263

* Author: xfalcox (Rafael Silva)
* Status: Open
* Priority: Normal
* Assignee: duerst (Martin D��rst)
* ruby -v: ruby 3.0.0dev (2020-12-16T18:46:44Z master 93ba3ac036) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
An issue caused by this bug was first reported at Discourse support community at https://meta.discourse.org/t/unicode-username-results-in-error-loading-profile-page/173182?u=falco.

The issue is that in Greek, there are two ways to downcase the letter ��������

 - �������� when it is used at the end of a word
 - �������� anywhere else

NodeJS follows this rule:

```
���  node
Welcome to Node.js v12.11.1.
Type ".help" for more information.
> "������������".toLowerCase()
'������������'
```

Python too:

```
��� python
Python 3.8.2 (default, Nov 23 2020, 16:33:30) 
[GCC 10.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> "������������".lower()
'������������'
```

Ruby (both 2.7 and 3) doesn't:

```
���  ruby --version           
ruby 3.0.0dev (2020-12-16T18:46:44Z master 93ba3ac036) [x86_64-linux]
���  irb           
irb(main):001:0> "������������".downcase
=> "������������"
```

```
���  ruby --version
ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux]
���  irb
irb(main):001:0> "������������".downcase
=> "������������"
```




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