Re: Reliable after-change-functions (via: Using incremental parsing in Emacs)

[Stefan Monnier]

> In C or C++ body files, "a complete parse" is typically one variable or
> function declaration. So if Emacs can reliably find the beginning and
> end of those declarations,

IIUC, a large part of CC-mode's trouble is exactly the need to find
somewhat reliably a position vaguely like "the beginning of
a declaration".

It's very much a non-trivial problem (and in the general case to
properly handle all possible comments you need to start parsing from
point-min).

>> And yes, doing this by consing strings is not a good idea, it will
>> slow things down and cause a lot of GC.  It is best avoided.  Thus my
>> questions above.
> I'm not sure how "convert syntax tree to elisp" compares to "consing
> strings". I would certainly expect it to cause a lot of GC.

If the GC is the worry, we can use a function which encodes the
buffer using a given coding-system and returns a malloc'd array of bytes.

>>> It's stored in a buffer-local variable. I haven't measured the memory
>>> they take. Memory is released when the tree object is garbage-collected
>>> (it's a `user-ptr').
> Is it an elisp structure (or accesible from elisp)? Have you written
> code that traverses it to provide faces and indentation?

According to https://github.com/tree-sitter/tree-sitter/issues/222 the
parse tree takes around 10 times the size of the source text.  At least
that's for tree-sitter's own parse-tree; not sure how that relates to
emacs-tree-sitter's yet.


        Stefan