bug#75164: treesit-font-lock-fontify-region is easy to lost color on parse error. suggest to remain fontify on parse error.

[Charalampos Mitrodimas]

Hi,

Eval Exec <execvy@gmail.com> writes:

> Hello.
> When I enable rust-ts-mode on a rust file, I found treesitter is easy
> to make emacs buffer to lost color.
> For example, on the following rust code:
> ```rust
>
> struct Dog {
>     name: String,
>     age: u8,
> }
>
>
> struct ManyStruct {
>     a: u8,
> }
>
> fn many_code(){
>     fn fib(n: u32) -> u32 {
>         if n == 0 {
>             return 0;
>         }
>         if n == 1 {
>             return 1;
>         }
>         fib(n - 1) + fib(n - 2)
>     }
> }
>
> fn main() {
>     // change below `//` to `/` to see the difference
>     // {
> }
> ```
>
> the rust code is right, and the emacs buffer color is right on every
> struct/functions.
> But, if I change `// {` to `/ {`, then the rust code is wrong, this
> buffer will lost all colors.

Thanks for reporting this.

I attempted to reproduce this, using your example, when I change `// {`
to `/{` only "main" from `fn main()` loses color. The rest of the syntax
highlighting remains intact in my setup.


                            C. Mitrodimas

> You can see the change on bellow images:
>
> https://imgur.com/a/4Tnv0GJ
>
> I suggest emacs can remain colors even if the code is wrong.
>
> My emacs version info: GNU Emacs 31.0.50