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

[Owen Voorhees via cfe-dev]

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 <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 <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 <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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