ui.log - support for coloring lines

[whoenig]

It would be nice if individual lines in ui.log could be colored (e.g., yellow for warnings, red for errors).

On the technical side, ui.log currently uses an html textarea, which does not support different text properties, as far as I know. (See https://github.com/zauberzeug/nicegui/blob/main/nicegui/elements/log.py and https://github.com/zauberzeug/nicegui/blob/main/nicegui/elements/log.js).

[rodja]

Indeed, this would be helpful. We would be happy to review any pull requests in this direction.

[falkoschindler]

I wonder how this could be done conceptually. Should we accept an optional color per line? Or should we add general support for HTML or maybe ANSI escape codes? And is it possible to keep using the existing implementation or should we switch to a more powerful JavaScript library like xterm.js (see #1846)?

[anoff]

Personally I prefer ANSI escape codes for compatibility reasons within the Python ecosystem.
In my current usecase I'm using https://pypi.org/project/colored anyway for styling the logs.

[whoenig]

On an API level the push function could get a color per line, or stylesheet definition, at least for my use-case. There might be cases where a more general support would be helpful (e.g., error messages in clang can highlight parts of the line to indicate clearly where a problem is).

On the technical side, I am not sure how to even get started. As stated in the initial feature request, the current implementation uses an textarena, which seems to only allow a single style for the whole text.

[WolfgangFahl]

I am simply prepending icons:

 LOG_LEVEL_ICONS = {
        logging.DEBUG: "🐞",
        logging.INFO: "ℹ️",
        logging.WARNING: "⚠️",
        logging.ERROR: "❌",
        logging.CRITICAL: "🔥",
    }