[cfe-dev] Clang Blank Attributes?

[Aaron Ballman via cfe-dev]

On Mon, Apr 17, 2017 at 7:25 AM, Farzad Sadeghi via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
> Let me first explain my situation.
> I'm developing a CFE-based tool called
> mutator(https://bloodstalker.github.io/mutator/). for the time being,
> mutator does some static checks(Misra-C:2004 and
> SaferCPP:http://duneroadrunner.github.io/SaferCPlusPlus/) and some
> automatic refactoring (mainly SaferCPP).
> mutator needs to have some sort of an options to let the users turn
> off diagnostics or automatic-refactoring for some parts of the code.
> And for that we need custom attributes.
>
> The thing with is, according to this
> document(http://clang.llvm.org/docs/InternalsManual.html#how-to-add-an-attribute),
> there is no other of way doing that other than modifying clang source
> code which causes all sorts of trouble with mutator's CI and the final
> packaging.
>
> I do not expect my patches to Attr.td and SemaDeclAttr.cpp to get
> accepted since they're dead code to anything other than mutator so it
> got me thinking.
>
> Would it be useful to add some blank custom attributes to clang that
> lets other similar tools use them as they see fit in MatchFinder
> callbacks?
> Roughly like:
>
> def BlankAttr01 : InheritableAttr {
>
> let Spellings = [CXX11<"clang", "blank_01">];
> let Subjects = SubjectList<[Var, Function, CXXRecord]>;
> let Documentation = [Undocumented];
> let Args = [BooleanArgument<"__bool01">];
> }
>
> case AttributeList::AT_BlankAttr01:
>   handleSimpleAttribute<BlankAttr01Attr>(S, D, Attr);
>   break;
>
> This way there are some blank attributes that can be used by tools(not
> in sema of course. my main point is for them to be used in matcher
> callbacks.) without having to modify clang source code.
>
> Thoughts? Suggestions?

I don't think we'd want to go with a blank attribute. However, we do
have an existing generic attribute (the annotate attribute), and we
have some patches towards pluggable attributes, if you wanted to put
in the effort to clean them up (I can send you the list if that's
something you'd be interested in working on).

~Aaron