bug#59693: 29.0.50; treesitter in base buffer doesn't respond to modifications in indirect buffer correctly

[Yuan Fu]

> On Nov 30, 2022, at 6:05 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> Cc: 59693@debbugs.gnu.org
>> From: Yuan Fu <casouri@gmail.com>
>> Date: Wed, 30 Nov 2022 02:17:14 -0800
>> 
>> Thanks! I forgot about indirect buffers... We’ll need to make sure to
>> use the parsers in the original buffer when user edits the indirect
>> buffer, or something like that. I need to look into how does indirect
>> buffer works.
> 
> In the insdel.c hooks where you record changes to buffer text, you should
> see if the buffer has a base_buffer, and if so, update any parsers of the
> base buffer as well.

Actually there’s a little bit of problem. When we edit the base buffer, we 
would want to update the parsers in all of its indirect buffers as well, and 
AFAICT there is no pointer from base buffer to the indirect buffer, only the 
other way around. 

We don’t want indirect buffer and base buffers to share parsers, since they can 
have different narrowing, and semantically indirect buffers should share 
anything but the text with the base buffer.

How about this: we change current_buffer->parser_list from a plain list of 
parsers to a cons (PARSER-LIST . INDIRECT-PARSER-LIST), where PARSER-LIST is as 
before. But for base buffers, INDIRECT-PARSER-LIST includes all the parsers of 
its indirect buffers; and for indirect buffers, INDIRECT-PARSER-LIST is nil.

Then base buffer can update all indirect buffers’ parsers, and indirect buffer 
can find its base buffer and update all the parsers, including the base 
buffer’s parsers and other indirect buffers’ parsers.

Of course, treesit-parser-create and treesit-parser-delete needs to do some 
extra work, but nothing complicated.

Yuan