[cfe-dev] parsing without building an AST tree

Anders Bakken agbakken at gmail.com
Wed Jul 18 20:14:31 PDT 2012

Hi Manuel

Well. We essentially provide a client/server setup where an editor can
pass a location (file,offset) to the server and some options and the
server can respond with various information. Most importantly
references to this location (from all the files we've indexed) and
whatever it refers to. This is to be able to do 21st century things
like "follow symbol" and "find references" in Emacs since I'll never
switch to an IDE. We need to be able to visit cursors I and ask them
what they reference I guess. Not sure if this would be possible with
the preprocess-only option. Likely not I guess. If you could point me
at an example on how to do the preprocessing only I'd love to have a

If you want to take a look at the project it can be found here:



On Tue, Jul 17, 2012 at 2:11 AM, Manuel Klimek <klimek at google.com> wrote:
> On Tue, Jul 17, 2012 at 10:07 AM, Anders Bakken <agbakken at gmail.com> wrote:
>> Hi
>> We're writing a clang-based tagger and while trying to improve the
>> performance of our solution we came upon this paragraph:
> Not sure what your requirements for a "tagger" are, would be curious :)
>> "Elsa is not built as a stack of reusable libraries like clang is. It
>> is very difficult to use part of Elsa without the whole front-end. For
>> example, you cannot use Elsa to parse C/ObjC code without building an
>> AST. You can do this in Clang and it is much faster than building an
>> AST."
>> from here: http://clang.llvm.org/comparison.html
>> We've been using the C-api in clang-c/Index.h but if we could get
>> better performance by using the C++ APIs directly we'd gladly do so
>> (even if it might change or be harder to use).
>> Is there an example or some documentation on how to do this somewhere possibly?
> You can use the clang preprocessor to tokenize if that's all you need.
> Currently there's not really good docs around that, and I don't think
> I have a really good example. I can get you some more ideas on how to
> go about this if you say that preprocessor-only is what you need.
> Cheers,
> /Manuel

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