Use style-dependent colour to highlight errors

[tgilgien]

Previously, the error highlighting would make it near impossible to read the code when using a dark theme.

	Default	Github-Dark
old
new

Unfortunately, pygments themes don't specify a colour for this specific purpose. The closest would be the error token colour, which however is meant to be used as a foreground colour. Using this would therefore mean to effectively loose the syntax highlighting on the affected lines, which is less than optimal.

My proposition would be to use the general highlight colour. While semantically less appropriate, it ensures that it remains readable with all themes.

[Bzero]

Thanks for bringing up this issue, I agree that the error background color should not be hard coded. It is a pity that the pygments styles only specify one generic highlight color.

I am not sure if it is a good idea to use the same color to highlight errors that is also used to highlight the current line however. Maybe one could do something similar to the highlighting of search results and modify the color a bit so it still fits the theme but is not the exact same:

typstwriter/typstwriter/editor.py

Line 1063 in 3e0ea19

highlight.format.setBackground(QtGui.QColor(self.highlighter.highlight_color).darker(120))

Speaking of, the underline error color is also hard coded:

typstwriter/typstwriter/editor.py

Line 913 in 3e0ea19

mark_span.format.setUnderlineColor("#cc1b1b")

Maybe the error token color could be appropriate for this one.

[tgilgien]

Speaking of, the underline error color is also hard coded:
Maybe the error token color could be appropriate for this one.

Agreed

For the main issue, I agree using the main highlight colour for different things isn't great, I forgot that you could highlight the current line.

Alternatively, pygments themes do define a special line number font and background colour, so we could highlight only the line numbers (though since they are hideable, we would need a fallback either way). What do you think of that?

Modifying the highlight colour would definitely work, but I'm not sure how easy it would be to make it look good with most themes, I'll need to experiment a bit.

[tgilgien]

@Bzero,
I think I got satisfying results by taking the saturation, brightness and alpha from the highlight colour and setting the hue to red:

With default theme:

With github dark theme:

I might look more closely at highlighting the line numbers, but I think a separate pull request would be more appropriate.

[Bzero]

Yes that sounds really good to me, that way we always get a red error color but with a brightness appropriate for the color theme. I think also highlighting the line numbers should not be necessary.

[Bzero]

Thanks a lot for this contribution!