From: sam.saffron@...
Date: 2020-12-17T02:40:29+00:00
Subject: [ruby-core:101486] [Ruby master Bug#17400] Incorrect character	downcase for Greek Sigma

Issue #17400 has been updated by sam.saffron (Sam Saffron).


Prior art here is: 

https://github.com/elixir-lang/elixir/issues/6437

https://github.com/elixir-lang/elixir/pull/6990/files

Rust

https://github.com/rust-lang/rust/issues/26035

Golang

https://github.com/golang/text/blob/master/cases/cases.go#L147-L152

--- 

Per https://dotnetfiddle.net/ 

```
using System;
					
public class Program
{
	public static void Main()
	{
		Console.WriteLine("������������".ToLower());
	}
}
```

.NET handles this. 


https://repl.it/languages/java10

```
class Main {  
  public static void main(String args[]) { 
    System.out.println("������������".toLowerCase()); 
  } 
}
```

Java handles this correctly

.... 

Seems annoying to carry this edge case, but the consensus out there is that we should carry it. 

----------------------------------------
Bug #17400: Incorrect character downcase for Greek Sigma
https://bugs.ruby-lang.org/issues/17400#change-89264

* 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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