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jank is C++

(jank-lang.org)
252 points Jeaye | 4 comments | 11 Jul 25 17:22 UTC | HN request time: 0.629s | source
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almostgotcaught ◴[11 Jul 25 18:15 UTC] No.44535360[source]▶
i commented on reddit (and got promptly downvoted) but since i think jank's author is around here (and hopefully is receptive to constructive criticism): the CppInterOp approach to cpp interop is completely janky (no pun intended). the approach literally string munges cpp and then parses/interprets it to emit ABI compliant calls. there's no reason to do this except that libclang currently doesn't support any other way. that's not jank's fault but it could be "fixed" in libclang. at a minimum you could use https://github.com/llvm/llvm-project/blob/main/clang/lib/Cod... to emit the code based on clang ast. at a maximum would be to use something like

https://github.com/Mr-Anyone/abi

or this if/when it comes to fruition

https://discourse.llvm.org/t/llvm-introduce-an-abi-lowering-...

to generate ABI compliant calls/etc for cpp libs.

note, i say all this with maximum love in my heart for a language that would have first class cpp interop - i would immediately become jank's biggest proponent/user if its cpp interop were robust.

EDIT: for people wanting/needing receipts, you can skim through https://github.com/compiler-research/CppInterOp/blob/main/li...

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Jeaye ◴[11 Jul 25 18:44 UTC] No.44535628[source]▶
Hey! I'm here and receptive.

I completely agree that Clang could solve this by actually supporting my use case. Unfortunately, Clang is very much designed for standalone AOT compilation, not intertwined with another IR generating mechanism. Furthermore, Clang struggles to handle some errors gracefully which can get it into a bad state.

I have grown jank's fork of CppInterOp quite significantly, in the past quarter, with the full change list being here: https://gist.github.com/jeaye/f6517e52f1b2331d294caed70119f1... Hoping to get all of this upstreamed, but it's a lot of work that is not high priority for me right now.

I think, based on my experience in the guts of CppInterOp, that the largest issue is not the C++ code generation. Basically any code generation is some form of string building. You linked to a part of CppInterOp which is constructing C++ functions. What's _actually_ wrong with that, in terms of robustness? The strings are generated not based on arbitrary user input, but based on Clang QualTypes and Decls. i.e. you need valid Clang values to actually get there anyway. Given that the ABI situation is an absolute mess, and that jank is already using Clang's JIT C++ compiler, I think this is a very viable solution.

However, in terms of robustness, I go back to Clang's error handling, lack of grace, and poor tooling for use cases like this. Based on my experience, _that_ is what will cause robustness issues.

Please don't take my response as unreceptive or defensive. I really do appreciate the discussion and if I'm saying something wrong, or if you want to explain further, please do. For alternatives, you linked to https://github.com/Mr-Anyone/abi which is 3 months old and has 0 stars (and so I assume 0 users and 0 years of battle testing). You also linked to https://discourse.llvm.org/t/llvm-introduce-an-abi-lowering-... which I agree would be great, _if/when it becomes available_.

So, out of all of the options, I'll ask clearly and sincerely: is there really a _better_ option which exists today?

CppInterOp is an implementation detail of jank. If we can replace C++ string generation with more IR generation and a portable ABI mechanism, _and_ if Clang can provide the sufficient libraries to make it so that I don't need to rely on C++ strings to be certain that my template specializations get the correct instantiation, I am definitely open to replacing CppInterOp. From all I've seen, we're not there yet.

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almostgotcaught ◴[11 Jul 25 18:54 UTC] No.44535716[source]▶
> which is 3 months old and has 0 stars (and so I assume 0 users and 0 years of battle testing)

ah my bad i meant to link to this one https://github.com/scrossuk/llvm-abi

which inspired the gsoc.

> is there really a _better_ option which exists today?

today the "best in class" approach is swift's which fully (well tries to) model cpp AST and do what i suggested (emitting code directly):

https://github.com/swiftlang/swift/blob/c09135b8f30c0cec8f5f...

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1. Jeaye ◴[11 Jul 25 19:07 UTC] No.44535835[source]▶
There are upsides to this approach. Coupling Swift's AST with Clang's AST will allow for the best codgen, for sure.

However, the huge downside to this approach, which cannot be overlooked, is that Clang (not libclang) is not designed to be a library. It doesn't have the backward compatibility of a library. Swift (i.e. Apple) is already deep into developing Clang, and so I'm sure they can afford the cost of keeping up with the breaking changes that happen on every Clang release. For a solo dev, I'm not yet sure this is actually viable, but I will give it more consideration.

However, I think that raising alarms at C++ codegen is unwarranted. As I said before, basically any query builder or codegen takes some form of string generation. The way we make those safe is to add types in front of them, so we're not just formatting user strings into other strings. That's exactly what CppInterOp does, where the types added are Clang QualTypes and Decls.

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2. almostgotcaught ◴[11 Jul 25 21:17 UTC] No.44536865[source]▶
> For a solo dev, I'm not yet sure this is actually viable, but I will give it more consideration.

look i'm not trying to shit on your project - i promise - i know calling you out like this publically almost requires a political kind of response (i probably shouldn't have done it). i agree with you that as a solo dev you can't (shouldn't) solve this problem - you have enough on your plate making jank great for your core users (who probably don't really care about cpp).

> As I said before, basically any query builder or codegen takes some form of string generation.

i mean this is a tautology on the level of "everything can be represented as strings". yes that's true but types (as you mention are important) and all i'm arguing is that it's much more robust to start with types and end with types instead of starting with strings and ending with types.

anyway you don't need to keep addressing my complaints - you have enough on your plate.

3. caim ◴[12 Jul 25 00:53 UTC] No.44538335[source]▶
You right. Always good to remember that Apple was and still is the main company behind LLVM.

Swift was built and its maintained by the same time that worked in LLVM.

And also, Swift has its own fork of LLVM and LLVM has built-in a lot of features designed for swift like calling convention and async transformation.

The amount of features swift has and is releasing at the same time it has its own LLVM version is just not a thing you can do without a lot of money and years of accumulated expertise.

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4. almostgotcaught ◴[12 Jul 25 04:05 UTC] No.44539205[source]▶
> still is the main company behind LLVM.

lol people really say whatever comes to their mind around here don't they? I'm pretty sure all of the companies associated with these targets would strongly disagree with you

https://github.com/llvm/llvm-project/tree/main/llvm/lib/Targ...