On Tue, Aug 30, 2016 at 11:29 PM, Thomas Martitz <kugel@rockbox.org> wrote:
Am 30.08.2016 um 21:10 schrieb Jiří Techet:

        Geany would then merge the tags, perhaps giving the plugin
        ones more
        weight, and store it in TM.


    I think you underestimate how many tags we're talking here. The
    example libclang ft-plugin would have to re-walk the entire AST
    (which is absolutely massive, particularly for C++), convert it to
    TM tag structures, and then Geany/TM would have to perform some
    merging logic, would would be more complicated than now if it was
    to support C++ properly, every single re-parse. My intuition tells
    me that just won't be fast enough, Clang already jumps through
    hoops and uses tricks to just build its own AST in-time.


I think it would be a disaster performance-wise. The number of AST nodes can be easily 100x more than the amount of tags we have from ctags (we get a single tag for a function now and AST will contain complete tree for the function body) so just this might cost 100x more. In addition all the necessary copies to TM internal representation, having to maintain the tree structure (in TM we use GPtrArrays for everything which are very efficient and during tag merge we try to eliminate even pointer dereferences because those start getting expensive when managing many tags) etc.


 Let's not outright reject possible solutions based on performance assumptions and guestimations. Performance can be evaluated on an actual implementation. Until then it's simply an invalid argument for this discussion. But FWIW, I don't think performance is the driving aspect.

No, performance is a very valid point. Tag updates don't happen in a background thread in Geany but rather on the main thread (and changing this would require lots of modifications as neither ctags, nor TM nor Geany are thread-safe) and all updates have to happen in a really short time period - you cannot make the GUI freeze while the user is typing so you have 100ms at most without any noticeable delay.
 

What's needed from the AST is tags (as you and I mentioned elsewhere, AST is the complete code representation, so much more than what's required currently). Those can be extracted in one pass. I don't see that tags need to be converted back to the original AST.

As Matthew said, tags are insufficient for good autocompletion (e.g. consider dynamic languages like Python where you have to infer variable type from the right-hand side of an assignment and based on that generate an autocompletion list).
 

For any successful plugin operation, the AST has to be generated (and probably re-generated regularly) and traversed at least once. Creating tags in a traversal that's happening done anyway probably isn't even going to add much overhead, if any.

But I assume AST is created in a background thread - as I said, all TM code runs on the main thread and everything has to happen fast enough between keystrokes so users don't experience any delays while typing.
 

As you say, we use a GPtrArray of tags because it's very efficient for sorting and merging. I think any ft-plugin will also have to sort (at least) for showing auto-completion and symbols tree - if it shows them itself. So it may even have to create such array/lists that TM uses anyway (you can't sort AST directly). So it might as well pass them to TM for sorting.

Whatever you do with tiny lists (say 1000 items) of tags which appear as a result of autocompletion doesn't matter. I'm talking about workspace array of tags which may contain all tags from a project with hundreds of thousands or millions of tags and which have to be updated as the user types and these updates have to be handled in a very efficient way.
 




And even if we did this, I don't know how we could handle ASTs of different languages in a generic way because these will differ significantly.


 One more time, seems I wasn't clear enough yet: I'm *not* suggesting that we create generic code inside Geany that handles any kind of AST. What I suggest is that plugins that use AST internally (or not) pass tag-like information to Geany, extracted and flattened from its internal AST (or whatever it uses). Then Geany and other plugins can use that information for their own purposes.

Again, for smart autocompletion you will need things from AST. 

The biggest problem of current scope completion in Geany is the lack of information about local variables which we might get with the new cxx ctags parser and add them to TM. We'll get better results then but still AST-based autocompletion will be able to do smarter things.

Cheers,

Jiri