Highlighting the colored URL in the "Open URL" window (and `textarea[]`) causes buggy text rendering

Luanti version

5.12.0

(but I remember seeing it in older versions)

Operating system and version

GNU/Linux

CPU model

No response

GPU model

No response

Active renderer

X11

Summary

If you click on a hyperlink in a hypertext formspec element that leads to an URL, Luanti shows a prompt window to ask you whether to open this URL or not. You can highlight the text with clicking and dragging on the URL in this window. The bug is that this may change the displayed text, causing a buggy rendering. Characters appear that are not part of the URL, other characters seem to disappear.

Example:

My guess is that this highlighting bug reveals the "true" text because the text contains color markings. I haven’t tested if this bug is limited to URLs only or if it’s a bug with colorization in general.

Steps to reproduce

1. In DevTest, start the formspec test with /test_formspec
2. Go to the Hypertext tab
3. Scroll down until you find "Action URL"
4. Click on "open URL"
5. Use the cursor to click and drag on the URL being shown
6. Repeat this and highlight different portions of the URL

Expected behavior: Highlighting just highlights the text, that’s it Actual behavior: Highlighting makes new characters appear out of nowhere and make others disappear