[Bug] Case-insensitive Page Title filtering does not match lowercase åäö

[ErikL98]

What happened?

The Page Titles filter is not fully case-insensitive for the Swedish characters å, ä and ö.

For example, searching for öppettider does not find the page title Öppettider.

However, Öppettider, ÖPPETTIDER and ÖpPeTtIdEr all find the same page title.

What should happen?

The Page Titles filter should be case-insensitive for Unicode characters as well.

Searching for öppettider should find Öppettider, just as searches with different casing of the other letters do.

How can this be reproduced?

1. Go to Behavior → Page Titles.
2. Search for Öppettider → the page title is found.
3. Search for ÖPPETTIDER → the page title is found.
4. Search for ÖpPeTtIdEr → the page title is found.
5. Search for öppettider → the page title is not found.

The issue appears to be related to the regex matching in:
core/DataTable/Filter/Pattern.php

The current code uses the case-insensitive regex modifier i:
preg_match($patternQuoted . "i", $string)

Changing it to use the Unicode modifier as well:
preg_match($patternQuoted . "iu", $string)

fixes the issue. After this change, öppettider correctly matches Öppettider.

The same issue is expected to affect å/Å and ä/Ä.

Matomo version

5.11.1

PHP version

8.4.3

Server operating system

No response

What browsers are you seeing the problem on?

No response

Computer operating system

No response

Relevant log output

Validations

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• Follow our Security Policy.
• Check that there isn't already an issue that reports the same bug to avoid creating duplicates.
• The provided steps to reproduce is a minimal reproducible of the Bug.

[tintubojan]

Hi @ErikL98

Thank you for creating the issue and bringing this to our attention, that's very appreciated. We have reviewed and triaged the problem internally, and we have confirmed it is an issue. Our team will prioritise this, and we will update you on the progress here when we have an update to share. If you have any further information or questions, please feel free to add them here.