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Re: Tree sitter support for C-like languages

From: Yuan Fu
Subject: Re: Tree sitter support for C-like languages
Date: Tue, 15 Nov 2022 02:51:31 -0800

> On Nov 14, 2022, at 7:27 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>> From: Yuan Fu <casouri@gmail.com>
>> Date: Mon, 14 Nov 2022 13:57:46 -0800
>> Cc: monnier@iro.umontreal.ca,
>> theo@thornhill.no,
>> emacs-devel@gnu.org
>>> Doesn't the call to ts_tree_edit update those nodes?  
>> No.
>>> That is, aren't
>>> those nodes a part of the tree that gets updated by the ts_tree_edit
>>> call?
>> The node stores some information in itself (start_byte, end_byte, inlined 
>> data, etc), and references the tree for the rest. The information it stores 
>> needs to be updated separately.
> Can we do that?  What are the difficulties?

We can update the nodes. (With ts_node_edit, similar to ts_tree_edit.)

But, I looked further, and the facility for updating a node is not really what 
we need/want. I won’t go into details here, because… there is a feature perfect 
for our use case! Tree-sitter can tell you what has changed when you re-parse a 
tree, that’s exactly what we need and very easy to use. It’s foolish for me to 
overlook this feature.

Specifically, when we re-parse a buffer, we can compare the before/after parse 
tree for differences. Tree-sitter can tell us the ranges in which nodes have 
changed during that re-parse. The “int” in the original example would be 
included in the ranges reported.

I’ve pushed a change that utilizes this feature. If you pull the latest commit 
and open c-ts-mode, error faces should appear and disappear as you type. There 
is no documentation for now, but basically we now allow users to register 
“after-change-function”s to tree-sitter parsers. The parser will call these 
functions when with the changed ranges when it re-parses.

The new functions are treesit-parser-add-notifier, treesit-parser-notifiers, 
treesit-parser-remove-notifier. I didn’t use 
treesit-parser-add-after-change-function because that is hideously long.


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