[llvm-dev] RFC: Adding a JSON library to LLVM Support

[Sam McCall via llvm-dev]

Finally following up here...

We ended up writing a JSON parser and checking it in under clangd/. We've
been using that for a while now without hitting new problems.
The header is here:
https://reviews.llvm.org/source/clang-tools-extra/browse/clang-tools-extra/trunk/clangd/JSONExpr.h
It's a DOM-based approach with objects on the heap. There's no streaming
parser, though one could be bolted on for e.g. long arrays. There are some
weak conventions around marshalling to structs with ADL functions. Compared
to what was described in my doc, it's simpler but less efficient, dropping
the arena representation.

(The reasons for not reusing an existing library were covered here:
https://groups.google.com/forum/#!topic/llvm-dev/5rryBKDY8eY)

There's at least some desire to reuse this more widely (I just talked to
Pavel about LLDB). So I'd propose lifting this up to llvm/Support/JSON.h.
(Dependencies are only Support and ADT).

Let me know if anyone has concerns!

On Fri, Oct 27, 2017 at 9:53 PM Sam McCall <sammccall at google.com> wrote:

> We don't have a dedicated JSON library in the LLVM tree, I'd like to add
> one. The pressing need is for clangd, but we have other tools that
> read/write JSON too.
>
> I'm proposing we write a new one, rather than importing a third-party
> library (licensing/integration reasons), on or extending YamlParser/YamlIO
> (usability/flexibility). I lean towards a design that parses a full DOM at
> once, and provides literal-like syntax for composing documents.
>
> I've written a document laying out the reasons for taking this path, and
> my proposal for a design (with links to a prototype)
>
> https://docs.google.com/document/d/1OEF9IauWwNuSigZzvvbjc1cVS1uGHRyGTXaoy3DjqM4/edit
> (Comments are enabled, but high-level discussion probably belongs on the
> list instead.)
>
> What do you think? I'm particularly interested in which parts of LLVM
> produce/consume JSON (or might want to), and what they need. I'm mostly
> familiar with the stuff in clang-tools-extra.
>
> Cheers, Sam
>
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