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

[Dmitry Gutov]

On 03/21/2016 06:45 PM, Vitalie Spinu wrote:

> Real trouble comes with continuation chunks. You might need to have a completely
> reversed indentation logic - in outer/host spans MM engine needs to call inner
> mode for indentation. Consider this example of erb mode taken from
> https://github.com/fxbois/web-mode/blob/master/tests/demo.erb.
>
>     <div id='header'>
>       <% if signed_in? -%>
>         <%= link_to t('.sign_out'), sign_out_path, :method => :delete %>
>       <% else -%>
>         <%= link_to t('.sign_in'), sign_in_path %>
>       <% end -%>
>     </div>

FWIW, I've successfully implemented indentation for ERB (and EJS) files 
without delegating to ruby-mode and js-mode indentation code:

https://github.com/purcell/mmm-mode/blob/c9a857a638701482931ffaaee262b61ce53489f3/mmm-erb.el#L157-L225

(it indents web-mode's example almost identically)

It should be easy to add support for similar types of files with almost 
the same code. But yes, it implies adding support for each new template 
format manually.

> One meaningful approach here is to indent if-else-end block using inner mode
> rules, right? This is what web-mode seems to be currently doing. Assume you are
> just in front of `<%= link_to`. This is host hmtl mode. But you need to indent
> according to inner mode construct. So what do you do? You go to the end of
> previous code chunk and call prog-indentation-function of inner mode with
> STRING-BEFORE = "\n" and STRING-AFTER="link_to t('.sign_out'), sign_out_path,
> :method => :delete". Simple isn't it? That's precisely my proposal.

It's simpler for the caller, but I'm having hard time imagining how to 
implement it properly on a major mode's side without inserting those 
strings into the buffer, or using a temporary buffer.

If STRING-BEFORE and STRING-AFTER are not allowed to contain newlines, 
yes, that becomes easier to handle, but that also loses in generality.