bug#22983: syntax-ppss returns wrong result.

[Dmitry Gutov]

On 03/11/2016 05:15 PM, Alan Mackenzie wrote:

> At this point, `ppss-1' and `parse' should match (apart from elements 2
> and 6).  What we actually have is:
>
>     ppss-1: (2 39992 nil nil nil nil 2 nil nil (39975 39992))
>     parse:  (0 nil 15674 34 nil nil 0 nil 15675 nil)

I think you mean that ppss-0 and ppss-1 must match independent of 
narrowing, and also match (parse-partial-sexp 1 40000).

Considering narrowing can change point-min arbitrarily, specifying 
(syntax-ppss pos) as (parse-partial-sexp (point-min) pos) is a losing 
proposition if you want consistency.

Alas, we have some code out there that implements multiple-major-mode 
functionality using narrowing and some hacking of syntax-ppss-last 
syntax-ppss-cache values.

Changing syntax-ppss to be independent of narrowing will break it, and 
we'll need to provide some alternative first.

We could introduce a syntax-ppss-dont-widen variable, though. Similar to 
font-lock-dont-widen.