The best way to select and highlight based on character coordinates

[ul]

For showing diagnostics and applying formatting kak-lsp needs to convert column coordinate in ranges sent by language servers from character offset to a byte offset. I see a few options to do that, please help me to figure out the best one.

1. Keep buffer copy in kak-lsp and analyze it to convert character offset to a byte offset.

Pros:

• Content of the buffer is anyway sent through the kak-lsp on every change, it's easy to keep the most recent version.
• I can be useful for solving other problems, i.e. Convert positions from LSP coordinates to Kakoune coordinates kakoune-lsp/kakoune-lsp#98 and, to a lesser extent, Consider using textEdit for completion kakoune-lsp/kakoune-lsp#40 or to make the lsp.kak side of applying formatting more straightforward.

Cons:

• Higher memory consumption.
• Duplicating editor's functionality.

2. Translate all coordinates on lsp.kak side by doing the following in the loop: position cursor using a character-based column with <line>g<column>l and extract byte offset with %val{cursor_column}

Pros:

• "Glue"-level change, keeps kak-lsp server and Kakoune from bloat, no duplication of functionality.

Cons:

• Extra shell<->Kakoune ping-pong for each coordinate, might introduce noticeable lag and need to be careful not to bump buffer timestamp while doing this.
• Probably not very maintainable shell code.

3. Add support for character-based range-specs to Kakoune

Pros:

• Might be easy to add to Kakoune as most likely all the necessary utilities are there already.
• Useful to other plugins (and already requested in Proposal: Select by character or display indices #2724).

Cons:

• Could be another "pet feature" which kakoune doesn't need as it's possible to accomplish the task with existing functionality.
• Performance hit?

[mawww]

Option 2. and 3. both have an additional con, which is that they only really work on current timestamp (Option 3 could handle other timestamps at the price of some implementation complexity), Option 1. does not have this problem as the lsp server and kak-lsp are already in sync regarding buffer state.

Option 2 might be implementable more efficiently now that we have echo -to-file ... to return the data back without forking a shell. (As an aside, a good part of kak-lsp scripting might be able to take advantage of that to reduce the amount of forking).

[ul]

Thanks for the suggestion! I decided to give the first option a go for now as it doesn't seem so bad in terms of resource consumption increase, but gives me opportunity to solve the problem (and its performance aspects) in the comfort of Rust, because I don't feel my skill of Kakoune+shell scripting being good enough to accomplish non-trivial task with confidence.