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Re: treesit indentation "blinking"

From: Daniel Colascione
Subject: Re: treesit indentation "blinking"
Date: Thu, 23 Mar 2023 17:10:53 -0400
User-agent: AquaMail/1.43.0 (build: 104300275)

On March 23, 2023 16:04:16 Yuan Fu <casouri@gmail.com> wrote:

On Mar 22, 2023, at 9:51 PM, Daniel Colascione <dancol@dancol.org> wrote:

On March 22, 2023 21:03:29 Yuan Fu <casouri@gmail.com> wrote:

On Mar 22, 2023, at 5:07 PM, Daniel Colascione <dancol@dancol.org> wrote:

On March 22, 2023 20:00:23 Yuan Fu <casouri@gmail.com> wrote:

On Mar 22, 2023, at 1:49 PM, Daniel Colascione <dancol@dancol.org> wrote:

Is there a general-purpose through which we can avoid line indentation
oscillating as the user types when the AST is temporarily invalid,
e.g. after '(' or '{'? I'm checking out the C++ tree-sitter mode, and
one of the more disconcerting things is the current line's indentation
changing rapidly as I type. Is it feasible to create ERROR recovery
indentation rules for every conceivable situation?

Yes, but in reality, I think all we need is a couple special case for the unmatched ( and {’s. Can you think of other cases of blinking indentations?


But TS reacts to missing closing brackets by clarifying the whole nearby _expression_ as ERROR. It's not, as would be more useful, saying "here's a stray (, and everything else is normal and parsed as if that ( were absent”

We can just look at the buffer text directly: if there’s an ERROR and the previous char (after skipping whitespace chars) is ( or {, we know what to do

Do we know what to do? That ERROR might be arbitrarily far up the parse tree. I don't think it's as easy as you think it might be. One strategy that might work is to see whether adding a "(" introduced an error, and, if so, temporarily replacing that "(" with whitespace, reparsing, and then using the resulting parse tree instead of the one with the "(" to do indentation and fontification. This way, I think you'd end up without the random jumping around we see today in TS modes.

We can place this special rule at the end of our rule list, and previous rules not matching should indicated “error” by itself. Of course, I can’t prove it by using this method to fix the blinking indent, but I don’t quite have the time for it right now.

Editing can cause all sorts of transient nonsense in the AST, and it's impossible to predict in a general manner what this nonsense might be. The wrong kind of bracket can cause the entire rest of the file to be parsed as nonsense. This or that error recovery rule isn't going to solve the problem: such a strategy is a fragile whack a mole. There needs to be some general solution to prevent indentation blinking. This blinking makes TS modules unusable for me.

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