Re: How to add pseudo vector types

[Yuan Fu <casouri@gmail.com>]

>> 
>>> Once again, we are talking about the function used by TS to read
>>> buffer text.  Not about the parser or its caller.  Low-level code,
>>> which knows nothing about the context, should never look beyond the
>>> restriction.
>> 
>> It doesn’t harm for tree-sitter to see the rest of the buffer, it doesn’t modify anything, all it does it reading the text. OTOH, restricting tree-sitter to the bounds of narrows adds complexity for no benefit (as far as I can see).
> 
> Which complexity does it add?  You just compare with BEGV_BYTE instead
> of BEG_BYTE etc.

We need to “delete” the hidden text and “re-insert” when we widen the buffer. I’ll try to make it a no-op as long as we remember to widen before calling tree-sitter to parse anything.

> 
> If we let TS look where it wants, we will lose the ability to restrict
> it to a certain part of the buffer text.  This is needed at least for
> some specialized modes, and is generally desirable, as it gives Lisp
> programs an easy way to impose such restrictions whenever they need.

Tree-sitter lets you set ranges for a parser to limit it self within, in order to support multi-language files.

> 
>> Maybe narrowing is the context that low level code should ignore
> 
> No other code in Emacs does, and for a good reason.
> 
>> The only benefit that I can think of is “we firmly adhere to the ‘contract’ that no one can look beyond the narrowed region”, but is it a good contract? Is there really a contract in the first place?
> 
> It served us very well until now, so yes, I think it's a good
> contract.
> 
>> IMO, narrowing acts like masking tapes over the rest of the buffer, so that user edits like re-replace wouldn’t spill out. Demanding everything in Emacs to not have access to the rest of the buffer is dogmatic (in the sense that it is too rigid and is simply following the doctrine blindly). 
> 
> Again, this "dogma" is used and adhered everywhere else in Emacs by
> such low-level code.

Ok. I trust you to know better than I do.

Yuan