Re: Guidelines for the "symbol" syntax class

[Dmitry Gutov <dgutov@yandex.ru>]

On 01/04/2016 02:55 AM, John Wiegley wrote:

> I suppose my informal guideline is to implement a strategy that works best for
> the mode you want to derive information from, and to not expect syntax classes
> to be a capable enough interface. I'd expect Ruby symbols to include ":",
> personally.

In c++-mode, `std::cout' is two separate symbols, so I'm going to follow 
that model.

> A::B is the qualified name of a symbol

Yes, and methods have qualified names like A::B#foo or A::B.bar, but we 
don't make `#' or `.' symbol constituents.

> -- although "B" is
> technically an unqualified symbol in its own right within that qualified name.

Yup. "B" is the name of a constant set on the module/class A. This is 
relevant because we can reference A::B from code lexically inside A (or 
even inside A::C) by its base name (B). And it's impossible to know 
whether the referenced constant (classes are constants, BTW) is B, A::B 
or A::C::B without runtime information, or parsing the whole project and 
its dependencies.

> Better yet, define a more general API that all modes can use, since many modes
> struggle with these same issues (imenu, thing-at-pt, dabbrev, etc). This
> echoes back to our long IDE thread.

Ouch. We do need to release 25.1 sometime. And I want 
xref-find-references to work okay-ish in ruby-mode by then.

There *are* some variables already in Emacs that I might have to use, 
and maybe I'm missing some of them. E.g. 
dabbrev-abbrev-skip-leading-regexp and find-tag-default-function (should 
xref-collect-references use find-tag-default-function?).

> Perhaps we need layered, semantically-
> defined classes, such that a given text position might occur within many such
> layers (for example, selection might choose B, A::B, or A::B.foo, depending on
> how many times I smash the "select current" key).

easy-kill defines a hierarchy of things (though a simplistic one), which 
works like you describe. How to apply that idea to dabbrev-expand and 
xref-find-references is not immediately obvious to me.