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

[Dmitry Gutov]

On 03/22/2016 08:17 PM, Vitalie Spinu wrote:

> This will not work in above case. <%else-%> chunk needs to know about where <%if
> signed_in? -%> was indented which is not an immediately preceding chunk.
>
> It's hard to think of better solution than collecting all relevant previous
> chunks in one place and indenting according to inner mode. In order to indent
> "<%else-%>", STRING-BEFORE should be full "link_to ..." line. So basically
> STRING-BEFORE must consist of all ruby spans in between "if" and "else" chunks.

...and the multi-mode package would have to know, somehow, that the "if" 
chunk is special in this regard, and know which "if" matches which 
"end", etc. Or simply always include all previous chunks in the given 
mode in STRING-BEFORE.

> > How should the "generic" code that links HTML and Ruby know when to indent
> > using the HTML indentation code and when to use the Ruby indentation rules?
>
> No idea. Dmitry should have an answer for that. He implemented mmm-erb.

Again, mmm-erb is written to support a limited set of template languages 
(currently, two, though supporting JSP would be trivial-ish, were 
java-mode not a part of CC Mode, with associated pitfalls).

So IME, the multi-mode package needs to hardcode, in some form of 
another, the knowledge which file formats use this approach to indentation.

And since we're doing that anyway, using a simpler indentation code in 
those particular files doesn't seem like a bad idea either. (For 
non-continuation hunks, at least).

BTW, web-mode doesn't seem to dispatch to inner modes's functions at 
all: 
https://github.com/fxbois/web-mode/blob/c5aacacb8f4c233844306806a102405c8e9671c9/web-mode.el#L7164-L7198. 
I'm not a fan of this approach in general, but that clearly means that 
it can work for indentation.