[ruby-core:121271] [Ruby master Bug#21176] Regression in case-insensitive matching for single-byte encodings

[ruby-core:121271] [Ruby master Bug#21176] Regression in case-insensitive matching for single-byte encodings

[ima1zumi (Mari Imaizumi) via ruby-core]

Issue #21176 has been reported by ima1zumi (Mari Imaizumi).

----------------------------------------
Bug #21176: Regression in case-insensitive matching for single-byte encodings
https://bugs.ruby-lang.org/issues/21176

* Author: ima1zumi (Mari Imaizumi)
* Status: Open
* ruby -v: ruby 3.5.0dev (2025-02-28T09:32:36Z master db4ea95219) +PRISM [arm64-darwin24]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
In Ruby 3.4.2, case-insensitive regex matching (`/i`) worked as expected for single-byte encodings like ISO-8859-x.
However, in Ruby 3.5.0dev, characters such as `\u00F3 (ó)` and `\u00D3 (Ó)` are no longer considered equivalent under case-insensitive matching, causing the match to fail.

The likely cause is #16145 , which appears to have broken handling of `0x80–0xFF` in single-byte encodings.

## Reproduction

```ruby
enc = Encoding::ISO_8859_1
o_acute_lower = "\u00F3".encode(enc)  # ó
o_acute_upper = "\u00D3".encode(enc)  # Ó

puts /[x#{o_acute_lower}]/i =~ "abc#{o_acute_upper}"
```

- Ruby 3.4.2: outputs 3 (match successful)
- Ruby 3.5.0dev: outputs nil (match fails)
    - ruby 3.5.0dev (2025-02-28T09:32:36Z master db4ea95219) +PRISM [arm64-darwin24]

I will submit PR to fix this.




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[ruby-core:121290] [Ruby master Bug#21176] Regression in case-insensitive matching for single-byte encodings

[ima1zumi (Mari Imaizumi) via ruby-core]

Issue #21176 has been updated by ima1zumi (Mari Imaizumi).

Description updated

;

----------------------------------------
Bug #21176: Regression in case-insensitive matching for single-byte encodings
https://bugs.ruby-lang.org/issues/21176#change-112254

* Author: ima1zumi (Mari Imaizumi)
* Status: Open
* ruby -v: ruby 3.5.0dev (2025-02-28T09:32:36Z master db4ea95219) +PRISM [arm64-darwin24]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
In Ruby 3.4.2, case-insensitive regex matching (`/i`) worked as expected for single-byte encodings like ISO-8859-x.
However, in Ruby 3.5.0dev, characters such as `\u00F3 (ó)` and `\u00D3 (Ó)` are no longer considered equivalent under case-insensitive matching, causing the match to fail.

The likely cause is #16145 , which appears to have broken handling of `0x80–0xFF` in single-byte encodings.

## Reproduction

```ruby
enc = Encoding::ISO_8859_1
o_acute_lower = "\u00F3".encode(enc)  # ó
o_acute_upper = "\u00D3".encode(enc)  # Ó

puts /[x#{o_acute_lower}]/i =~ "abc#{o_acute_upper}"
```

- Ruby 3.4.2: outputs 3 (match successful)
- Ruby 3.5.0dev: outputs nil (match fails)
    - ruby 3.5.0dev (2025-02-28T09:32:36Z master db4ea95219) +PRISM [arm64-darwin24]

I will submit PR to fix this.

https://github.com/ruby/ruby/pull/12889




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