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

[Alan Mackenzie]

Hello, Dmitry.

On Sat, Mar 12, 2016 at 12:38:49AM +0200, Dmitry Gutov wrote:
> On 03/12/2016 12:15 AM, Alan Mackenzie wrote:

> >> Except the multiple-major-mode case, which we'd ideally try to
> >> accommodate, too.

> > How does this code handle the changeover of syntax tables at a mode
> > boundary?

> The "inner" regions start with an "empty", top-level state. This is 
> actually fine, because these are usually small enough not to benefit 
> from the syntax-ppss cache too much (and syntax-ppss-last still helps).

> The parts of the outer region following a subregion with different 
> syntax table... rely on a few hacks, and a manual application of a 
> `syntax-table' property when necessary. We need a better solution there, 
> but it's probably out of scope for this discussion.

How about an extension to the parse-partial-sexp (etc.) code?  For
example, a feature I would call an "island", where a character could be
marked with the "island start" syntax-table property, and another
character lower down could be marked with the "island end" character.
parse-partial-sexp, on encountering an island start syntax would somehow
stack the current parse state and start a new one with a different syntax
table.  The parse state, instead of consisting of the 10 elements
currently, would in general have 10n elements, where n is the depth of
nesting.

-- 
Alan Mackenzie (Nuremberg, Germany).