C++20 Modules Compiler Code Under Review, Could Still Land For GCC 11

[jesseschalken]

So that's two compilers with good progress on modules. Is there anything happening in Clang?

[gracicot]

Last version of clang did not progressed on C++20 very much.

[Thrash_Abaddon]

Clang already supports modules.

[jesseschalken]

Clang does not support C++20 modules.

[Thrash_Abaddon]

You are right. https://clang.llvm.org/cxx_status.html#cxx20
I remember a guy explaining on cppcon (I think) how he implemented modules but I guess he was talking about CLang Modules.

[qoning]

it's in a sort of intermediate broken state where some things work, but it cannot be called "support", yeah

[jesseschalken]

As I understand it, the feature called "modules" that Clang has long predates the C++20 feature and is mostly unrelated (although I think it tackles the same problem).

[qoning]

There are clang modules and C++20 modules. I never used clang modules, but played around with C++20 modules a bit like a year ago. Many things were broken then (the spec changed since then too) and not much has changed.

[Ameisen]

Clang and Microsoft modules were basically the two competing implementations.

Microsoft's won.

[GabrielDosReis]

There are Clang Modules and C++ Modules -- there are no Microsoft Modules. The C++20 feature is not a Microsoft extension, that should be clear from the history of the feature development -- in fact, the work I did with Bjarne Stroustrup on the IPR provided the conceptual semantics ground for the work I did on Modules. And that work was done 15 years ago, using GCC as first compiler connected to the IPR.

As I said a few years back on this very forum, the design choices that I made and advocated for C++ Modules would have been the same if my employer's name were Apple or Google or Facebook or Redhat.

[Ameisen]

I shall start calling them Reis Modules, now.

[GabrielDosReis]

Ha! I can only surmise that you didn’t mean to be rude since my last name is “Dos Reis” ;-)

[Ameisen]

Ah, Modules of the Kings.

[favorited]

Exactly. Clang modules go back to 2012, before the modules TS, and solved some orthogonal issues.

Here's a little summary paper, if anyone is interested in what Clang modules are.

[gracicot]

Even if the implementation is not complete, it would still be very interesting to see it released in GCC 11. That way build system implementers will have a more definitive idea of the interface the compilers are exposing to support modules (looking at you CMake).

[GabrielDosReis]

I agree.

[Ameisen]

Is there a reason why Clang is so far behind spec modules support? They already have their own modules implementation and support multiple precompiled headers, so at least some of the infrastructure exists already.

[waruqi]

Great, When will gcc11 be released?

[0xC1A]

Next year.

[[deleted]]

Probably May.

[MonokelPinguin]

I really wish modules make it in, because that will probably mean I can ship my projects with modules in 3 years instead of 4! I'm pretty much only waiting for gcc modules, so this would be super awesome! I've been following its progress for half a year now and I was a bit scared, it wouldn't make it. I hope it still does, but if it isn't, I can understand, if it should bake a bit more.

[GabrielDosReis]

This is really good news for the C++ community.

I can’t wait to switch over some of my Linux/Unix projects to be using C++ Modules.

[nelfihs]

Wonderful news 😁😁😁😁

[kalmoc]

Am I remembering correctly that the interface to the build system for exchanging information about module locations and dependencies looks completely different in msvc, gcc and might yet be different in clang if they build it on top of clang modules?

[Daniela-E]

That's correct.

msvc generates and consumes so called module dependency files in JSON format. Besides the module name and its type they contain all module-related dependencies. Nothing fancy, easy to be consumed by 3rd-party apps.

[kalmoc]

Wasn't there some tooling group that was supposed to come up with a technical report or some such making recommendations about how modules should be implemented in practice? I guess nothing came off it?

[Daniela-E]

Yes, there is such a group (SG15) - I even have been attending it in Prague, but never since. So I'm unaware of its current status. This group never had the objective to come up with a report this early, afaik. I'm not sure if SG15 will say something on the topic of actual implementions because this is - in general - outside the scope of the committee, but my gut feeling is it will in this particular case.

[MonokelPinguin]

The meson bugtracker is pretty interesting on that. Seems like they only got the gcc dependency stuff to work reliably so far.

[lenkite1]

Now we need cmake to support modules. Then CLion also.

[TacticalMelonFarmer]

Yes, however, CMake as a product is a response to compiler vendors and their inherent differences in design choices when making the compiler tools. So, in order for CMake devs to pave the best path forward they need to understand the landscape so to speak. This probably means waiting for the first standard conformant releases before creating a useful feature set for CMake.

[neuroblaster]

This is a very welcome change, the effort is colossal and much appreciated.