[cfe-dev] [RFC] Upstreaming proposed change to .dia format from Swift

Aaron Ballman via cfe-dev cfe-dev at lists.llvm.org
Tue May 19 05:44:03 PDT 2020

On Tue, May 19, 2020 at 6:26 AM Finkel, Hal J. <hfinkel at anl.gov> wrote:
> Hi, Owen,
> I think having documentation links associated with diagnostics is a useful feature, and I would be happy to see it in Clang.

I agree, I think this is a great idea! Hopefully we can also make use
of it (or something like it) in clang-tidy as well.

> I would encourage the addition of appropriate links to Clang's https://clang.llvm.org/docs/LanguageExtensions.html and, moreover, maybe we can generate these for mis-applied attributes in some automated way (given that our attribute docs are also TableGen-generated).

Are you envisioning something like `[[gnu::nonnull]] int *i;` giving
you a diagnostic about the attribute being ignored because it doesn't
apply to local variables, along with a link directly to the
documentation for that attribute? If so, that's a neat idea! We could
possibly even do something like that for unknown or misspelled command
line arguments, because the command line reference is also table


>  -Hal
> Hal Finkel
> Lead, Compiler Technology and Programming Languages
> Leadership Computing Facility
> Argonne National Laboratory
> ________________________________
> From: cfe-dev <cfe-dev-bounces at lists.llvm.org> on behalf of Owen Voorhees via cfe-dev <cfe-dev at lists.llvm.org>
> Sent: Monday, May 18, 2020 10:15 AM
> To: cfe-dev at lists.llvm.org <cfe-dev at lists.llvm.org>
> Subject: [cfe-dev] [RFC] Upstreaming proposed change to .dia format from Swift
> Hi all,
> I was hoping to get some feedback on a proposed change to clang's serialized diagnostics format.
> To give some background, Swift (swift.org) also uses this format for its diagnostics, and we recently added a new feature called "educational notes" which we'd like to start serializing. An educational note is attached to a diagnostic and is essentially just a path to associated documentation somewhere in a compiler toolchain. The documentation can then be displayed alongside emitted diagnostics to teach users about relevant language concepts or describe common problems and solutions. More details can be found at https://github.com/apple/swift/blob/master/docs/Diagnostics.md#educational-notes and an example is available at https://github.com/apple/swift/blob/master/userdocs/diagnostics/temporary-pointers.md.
> In order to support this use case, I'd like to propose adding new records to the .dia format for educational note paths, or perhaps more generally, documentation paths. The new records would be emitted alongside the main diagnostic record, similar to the handling of ranges and fix-its. I've submitted a patch with the proposed changes here: https://reviews.llvm.org/D80126 .
> The main reason we'd like to upstream this change to Clang instead of just implementing it in Swift is to avoid diverging from the established format. However, it isn't language specific and in the long term I think this is a feature that could benefit Clang's diagnostics quite a bit as well.
> My questions are:
> Is the clang community open to making a change like this that primarily benefits a downstream project (swift) in the short term?
> Is this a feature clang might be interested in adopting at some point?
> Any and all feedback is welcome! Sorry if this is the wrong place to discuss this sort of thing — it's my first time posting to the LLVM lists.
> Thanks,
> Owen

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