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Re: How to add pseudo vector types

From: Yuan Fu
Subject: Re: How to add pseudo vector types
Date: Sat, 24 Jul 2021 11:04:35 -0400

I wrote a simple interface between font-lock and tree-sitter, and it works 
pretty well: using tree-sitter for fontification, xdisp.c opens a lot faster, 
and scrolling through the buffer is also perceivably faster. My simple 
interface works like this: tree-sitter allow you to “pattern match” nodes in 
the parse tree with a DSL, and assign names to the matched nodes, e.g., given a 
pattern, you get back a list of (NAME . MATCHED-NODE). And if we use font-lock 
faces as names for those nodes, we get back a list of (FACE . MATCHED-NODE) 
from tree-sitter, and Emacs can simply look at the beginning and end of the 
node, and apply FACE to that range. For flexibility, FACE can also be a 
function, in which case the function is called with the node. This interface is 
basically what emacs-tree-sitter does (I don’t know if they allow a capture 
name to be a function, though.)

I have an example major-mode for C that uses tree-sitter for font-locking at 
the end of tree-sitter.el. 

Main functions to look at: tree-sitter-query-capture in tree_sitter.c, and 
tree-sitter-fontify-region-function in tree-sitter.el.

On the font-lock front, tree-sitter-fontify-region-function replaces 
font-lock-default-fontify-region, and tree-sitter-font-lock-settings replaces 
font-lock-defaults and font-lock-keywords. I should support 
font-lock-maximum-decoration but haven’t came up with a good way to do that. 
Maybe I should somehow reuse font-lock-defaults, and make it able to configure 
for tree-sitter font-locking? Apart from font-lock-maximum-decoration, what 
else should tree-sitter share with font-lock?

BTW, what is the best way to signal a lisp error from C? I tried xsignal2, 
signal_error, error and friends but they seem to crash Emacs. Maybe I wasn’t 
using them correctly.

IIUC if we want tree-sitter to use our malloc, we need to build it with Emacs, 
where should I put the source of tree-sitter?

What’s the different between make_string and make_pure_c_string? I’ve seen this 
“pure” thing else where, what does “pure” mean?


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