Re: Writing syntax-propertize-function for strings in code in strings, etc

[Dmitry Gutov]

On 08.09.2012 23:31, Stefan Monnier wrote:
> > Sublime Text handles these aspects rather excellently, and even
> > highlights the code inside as code, not string contents:
> > http://i.imgur.com/NH1Ye.png
> > Is there a proper way to do so in Emacs?
>
> Currently, it's pretty difficult for Emacs to handle it like in the
> picture above.
>
> > My first idea was, when propertizing interpolation, to see what kind of
> > string we're inside, and apply the appropriate syntax to the enclosing
> > braces, thus splitting the literal in two.  But (a) string quotes class
> > doesn't work that way (text characters on both ends of a literal must
> > be the same), (b) if we're inside a percent literal (syntax class:
> > generic string), and the literal spans several lines, we need to be able
> > to jump to its real beginning position from its end, but with this
> > approach (nth 8 (syntax-ppss)) will just return the beginning of the
> > last piece.  Saving buffer positions to text properties looks not very
> > reliable, since the respective text may be deleted and re-inserted.
>
> > Suggestions?
>
> I think the better approach is to extend syntax.c with such a notion of
> "syntax within strings".  This could hopefully be used for:
> - Strings within strings (e.g. Postscript nested strings).
> - Comments within strings (I think some regexps allow comments).
> - Code within strings (as here and in shell scripts).
> I'm not sure what that would look like concretely.  Maybe a new string
> quote syntax which specifies a syntax-table to use within the string?

In the current case, the syntactic meanings of characters are the same 
as outside the string, except a certain character should end the "inner" 
region and return the state after it to "inside string" (*).

Maybe just two new classes, similar to open and close parenthesis (to 
support nesting)?

* Preferably, only when it's not inside an "inner" string or comment.
At least, that's how it works in Ruby 1.9:

irb(main):011:0> %(#{"})"})
=> "})"

irb(main):013:0> %(#{#})
irb(main):014:0> })
=> ""

The above examples also won't work with current percent literals 
handling, but that's less important, I think.

parse-partial-sexp will probably need to keep some sort of stack for 
string-related data, so that when we're after the end of an "inner" 
region, we could find out what is the outer string's type and where it 
started.
And when inside the inner region, the position of its start.
Use the 9th state element and bump the total number to 10?