From: "mame (Yusuke Endoh)" <noreply@...>
Date: 2022-02-21T03:44:59+00:00
Subject: [ruby-core:107678] [Ruby master Bug#18590] String#downcase and CAPITAL LETTER I WITH DOT ABOVE

Issue #18590 has been updated by mame (Yusuke Endoh).


@duerst Looks like this document https://www.unicode.org/charts/case/ (which is referred by https://docs.ruby-lang.org/en/master/doc/case_mapping_rdoc.html) says that the lowercase of U+0130 is U+0069. Which is correct?

----------------------------------------
Bug #18590: String#downcase and CAPITAL LETTER I WITH DOT ABOVE
https://bugs.ruby-lang.org/issues/18590#change-96597

* Author: andrykonchin (Andrew Konchin)
* Status: Assigned
* Priority: Normal
* Assignee: duerst (Martin D��rst)
* ruby -v: 3.1.0p0
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
Downcasing for "��" character works in an unexpected way:

```ruby
'��'.downcase
=> "i��"
```

Expected result - downcasing should return "i". Instead, it returns small "i" and additional "dot" character:

```ruby
'��'.downcase.chars
=> ["i", "��"]
```

According to the standard Unicode case mapping character '��'(0130) maps to lowercased 'i' (0069).

```
0130;LATIN CAPITAL LETTER I WITH DOT ABOVE;Lu;0;L;0049 0307;;;;N;LATIN CAPITAL LETTER I DOT;;;0069;
```

https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt




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