[cfe-dev] libclang documentation/comments API

Kevin Funk via cfe-dev cfe-dev at lists.llvm.org
Sun Sep 6 10:50:27 PDT 2015

On Sunday, September 06, 2015 05:54:01 PM Ben Jackson via cfe-dev wrote:
> Hi there,
> I’m working on a feature for querying and returning documentation data in a
> libclang-based code comprehension engine (ycmd -
> https://github.com/Valloric/ycmd <https://github.com/Valloric/ycmd> ). The
> idea is, for a given cursor, return meaningful documentation for display to
> a user in their IDE (i.e. “What is the doxygen documentation for the method
> under my cursor?” ).
> I have found that there is quite rich support for doxygen comment parsing
> within clang, and most (all?) of it is exposed in libclang. This is
> awesome! Thanks!
> However, I do have a few questions about the current level of support:
> 1. The “comment introspection” API is not listed (here:
> http://clang.llvm.org/doxygen/modules.html
> <http://clang.llvm.org/doxygen/modules.html>) as part of “libclang”. Does
> that mean that the API is not public or not stable in some way? The docs
> say “These facilities are distinct from the core and may be subject to
> their own schedule of stability and deprecation”… I’m just curious as to
> how much this is likely to be an issue?
> 2. Is there any way via libclang to get the raw text, or any other
> pretty-printed text,  of a particular declaration? The idea here is that I
> could present the declaration text, followed by its brief and any other
> documentation. The declaration text itself is probably the most useful
> documentation for a developer :).Currently I am actually getting this by
> calling clang_FullComment_getAsXML() and parsing the output to get the
> “<Declaration>” element, but that seems painfully wasteful.

As last resort, we in KDevelop have our brute-force method of extracting raw 
text from a source range, see ClangUtils::getRawContents here:
  (not the most performant solution either, but helps getting "what the user 
> 3. I guess finally, do you have any other thoughts or has anyone approached
> this before or know of an implementation doing this sort of thing, etc. Any
> feedback would be greatly appreciated. :) If anyone is interested, a quick
> demo is here: http://www.gfycat.com/AlertNarrowAntelopegroundsquirrel
> <http://www.gfycat.com/AlertNarrowAntelopegroundsquirrel>

We already use it in kdev-clang as well. In our case we simply show the 
documentation in the context browser popup in case the user a) hovers a 
declaration with the mouse, or b) presses "Alt" when over a declaration with 
the cursor. (Alt+Keys then also allows navigation within the popup).

See here:


> Many thanks,
> Ben
> P.S. Apologies if this list is not for this sort of query :/

Kevin Funk | kfunk at kde.org | http://kfunk.org
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