I could swear I recently saw an article about a peg-tool that came with lsp support - sadly I can't find it. The closest I come is pest which has an ide-tools crate and some plugins for lsp/ide/editor support:
I have been on the lookout for something that code help me with Jinja files and it seems like a plausible candidate. Extra bonus points if I could actually embed the Python in the same grammar but at this point even having the code blocks segregated from the literal parts is a good start
https://github.com/pest-parser