Re: State of the overlay tree branch?

[Eli Zaretskii <eliz@gnu.org>]

> From: Sebastien Chapuis <sebastien@chapu.is>
> Cc: Sebastian Sturm <s.sturm@arkona-technologies.de>, emacs-devel@gnu.org
> Date: Wed, 21 Mar 2018 15:14:18 +0100
> 
> The language server protocol defines a position in file with zero-indexed
> line and column offsets [1]:
> 
> ```
> interface Position {
> 	line: number;
> 	character: number;
> }
> ```
> 
> lsp-mode uses heavily line-number-at-pos to convert an Emacs buffer
> point to a LSP position, and vice-versa [2].

line-number-at-pos is inefficient, in that it always counts from the
beginning of the buffer.  By keeping already computed line numbers
around, you could make a faster implementation if you count relative
line offsets using count-lines instead.

> This can happen thousands times on each keystroke.

_Thousands_ times for _each_ keystroke?  Why is that?  Most keystrokes
only change a single line, so how come you need thousands of lines
recounted each time?

> If Emacs could provide a function to do the conversion very fast (or at
> least faster than with line-number-at-pos), it would be great.

Given the above, I think you need to describe the issue in more
details, before we even begin designing the solution.