Re: Syntax tables for multiple modes [was: bug#22983: syntax-ppss returns wrong result.]

[Dmitry Gutov]

On 03/20/2016 12:51 AM, Vitalie Spinu wrote:

> You can simulate islands by marking inner spans as comments with comment classes
> (11 and 12).

Ooh, that's a solid idea. Should be more generic that my "propertize <> 
as punctuation" approach.

> I used those in polymode in the past, but not anymore. It's not
> that useful. Most of the parsing that modes do is regex based.

I'd say it's still useful. Without the above, I've had indentation 
problems with sgml-mode.

A good mode would use syntax-ppss to check that point is not inside a 
string or comment. Maybe that's not often done in font-lock, but it's at 
least common in syntax-propertize and indentation functions.

Example: sgml-lexical-context. It performs a search at first, but in the 
end uses parse-partial-sexp, and returns a value based on that status.

> So if a mode
> author decides to regexpf for a wiki link on a full buffer after widening it,
> islands won't help.

Where does widening happens in this case? First, we have 
font-lock-dont-widen.

For indentation, we've introduced prog-indentation-context recently. And 
indentation functions in programming modes are supposed to call 
prog-widen instead of widen now.

syntax-propertize-function's aren't supposed to call widen at all, I think.

> IMO the most useful direction for multi-modes is to add a hard narrowing that
> Stephen mentioned in the other thread. `syntax-ppss-dont-widen` goes in that
> direction, but it doesn't address the issue of distinguishing between user
> narrowing and "hard narrowing" in multi modes.

syntax-ppss-dont-widen and prog-indentation-context will be the 
indicators of the "hard narrowing", I guess.