Add syntax highlighting for KDE/Kate

[larsgw]

I would like, at some point, to add syntax highlighting for KDE and the Kate editor. They use a custom XML-based format, so I doubt we can easily reuse existing syntax highlighters, though I don't exactly know which of those there are already.

Documentation: https://docs.kde.org/stable5/en/kate/katepart/highlight.html
Example syntax definition for TOML: https://invent.kde.org/frameworks/syntax-highlighting/-/blob/master/data/syntax/toml.xml

[larsgw]

Wow, a lot of this is really difficult, if not impossible. One essential feature for me is different colors for node names and property keys, but that pretty much impossible when considering multiline strings & comments.

[zkat]

@larsgw LSP supports semanticTokens, which lets you augment an editor's built-in, simplistic syntax highlighting with additional semantic stuff. KDL is such that you should be able to do all necessary highlighting purely with a static engine, but it's definitely harder to do some things depending on what you're using. tmLanguage sucks, for example.

[larsgw]

Thanks for the info!

LSP supports semanticTokens, which lets you augment an editor's built-in, simplistic syntax highlighting with additional semantic stuff.

I don't know the extent of support for LSPs in Kate, and I'd like to at least provide some basic syntax highlighting without it. I think it could be shipped by default as well if it's included in https://invent.kde.org/frameworks/syntax-highlighting.

KDL is such that you should be able to do all necessary highlighting purely with a static engine, but it's definitely harder to do some things depending on what you're using. tmLanguage sucks, for example.

This one has look-aheads, but only using a RegExpr and while staying on the same line (which is an undocumented limitation). Regardless, RegExpr is insufficient for nested /**/ comments.

[larsgw]

There we go: https://github.com/larsgw/katepart-kdl

[zkat]

@larsgw make sure to add it to the README and kdl-org.github.io!