[PATCH] D31343: Add an attribute plugin example

[Erich Keane via Phabricator via cfe-commits]

erichkeane added a comment.

In D31343#1937588 <https://reviews.llvm.org/D31343#1937588>, @aaron.ballman wrote:

> In D31343#1936810 <https://reviews.llvm.org/D31343#1936810>, @Jasmin wrote:
>
> > Hello John!
> >
> > I was encouraged by Erich after a talk I had with him and Aaron on IRC to contact you about an use case for this plugin.
> >
> > I wanted to use user-specified/unknown attributes to annotate code and was told that they are not propagated through
> >  the AST and therefore it is not possible at the moment to use them for that purpose. Aaron's and Erich's idea was to
> >  allow kind of no-op attributes in the plugin so that the compiler would not issue a warning about the unknown attribute.
> >  This would be helpful for the user being able to define a list of attributes the user knows and expects, so that a compilation
> >  would not be spammed unnecessarily and misspelled attributes would still stand out.
> >
> > Being able to get the cursor or displayName of the attribute would essentially be enough to use it in tooling.
> >
> > We can use __attribute__((annotate(smth))) at the time being to achieve the same goal, but it is much more writing to do
> >  and also vendor specific. Being able to do the same with attributes would give them a real purpose, other than having
> >  to be accepted and not causing an error. Also they have to be supported by the language and we don't have to use
> >  macros to annotate the code.
> >
> > To summarize it would be nice to have:
> >
> > - user supplied unknown attributes to suppress a warning
> > - unknown attributes propagated in the AST
> >
> >   I hope I summarized this correctly and could get through the gist of this idea.
> >
> >   Looking forward to hearing from you.
>
>
> For reference: the current set of patches John has been working on allow you to load a plugin to let the frontend parse an attribute with an arbitrary spelling, but it does not have a way for you to register a new attribute AST node that gets attached to anything in the AST. Instead, you create an existing semantic attribute (such as an `AnnotateAttr`) and add that to the AST.
>
> I think this is a great request to keep in mind for John or anyone else who wants to extend this plugin functionality to allow for generating custom attribute AST nodes (which is of interest for tools like clang static analyzer or clang tidy plugins that may consume the clang AST). This functionality would also have to keep the libclang C indexing interface in mind, as that's another area of the compiler where this functionality would be useful.


Hmm... I wonder if there is value to having these plugin-attributes auto-create a PluginAnnotateAttr or something (some otherwise bikeshedded attribute) for exactly Jasmin's use case.  That way the plugin author simply needs to list the possible spellings.


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https://reviews.llvm.org/D31343