From: mame@...
Date: 2020-12-17T03:07:23+00:00
Subject: [ruby-core:101487] [Ruby master Bug#17400] Incorrect character	downcase for Greek Sigma

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


Oops, my understanding seemed to be wrong. Please forget my previous comment. When the next letter is an apostrophe, the further next letter seems to determine, but I don't understand this behavior from the code of v8. I leave it to an expert.

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

----------------------------------------
Bug #17400: Incorrect character downcase for Greek Sigma
https://bugs.ruby-lang.org/issues/17400#change-89265

* 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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