[cfe-dev] Clang-based autocompletion speed

[Val Markovic via cfe-dev]

For YCM, we pass a the CXTranslationUnit_Incomplete flag
<https://github.com/Valloric/ycmd/blob/master/cpp/ycm/ClangCompleter/TranslationUnit.cpp#L38>
that provides a massive boost to performance. It doesn't do what you're
asking for though (which BTW would be great).

On Thu, Jan 7, 2016 at 1:34 PM, Maksym Taran <mtaran at google.com> wrote:

> Hello!
>
> I'm looking into improving how an autocomplete system at Google computes semantic
> autocompletions for a given C++ file + line + column. Currently, it's
> mostly just calling out to clang_codeCompleteAt
> <https://github.com/llvm-mirror/clang/blob/52ed5ec631b0bbf5c714baa0cd83c33ebfe0c6aa/tools/libclang/CIndexCodeCompletion.cpp#L798>,
> and that's where we've been seeing high latency.
>
> A particular problem we're having is that when we try to autocomplete just
> within some scope (that is, just inside a function body, rather than after
> a . or -> etc), calling that method returns *all* possible autocompletion
> results, which includes all constants and class names defined in all the
> transitively included files as far as I can tell. This is technically
> correct, but in practice takes on the order of seconds to return, which is
> much longer than the desired timeframe for autocompletion results. So I'd
> like to know if there's some way I can get a smaller set of autocompletions
> more quickly, e.g. by asking clang to complete only on method names and
> locals, or by giving a time limit to get results. I didn't see how I might
> do that in the documentation
> <http://clang.llvm.org/doxygen/group__CINDEX__CODE__COMPLET.html#ga50fedfa85d8d1517363952f2e10aa3bf> so
> I'm wondering if there are some other APIs I'm not seeing.
>
> I took a look at YouCompleteMe <https://github.com/Valloric/YouCompleteMe>
> and it's using the same API
> <https://github.com/Valloric/ycmd/blob/master/cpp/ycm/ClangCompleter/TranslationUnit.cpp#L176>,
> so I suspect it might have the same problem. If there's no way to do
> something like this using the current API methods, I'd be interested to
> know how possible/difficult would it be to implement additional methods or
> options?
>
> Thank you!
> Maksym
>
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