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Re: Scheduling a virtual meeting to discuss where the std module source file should live

From: Gabriel Dos Reis <gdr_at_[hidden]>
Date: Mon, 11 Dec 2023 14:38:32 +0000
Is the experience dependent on the platforms?

-- Gaby

From: SG15 <sg15-bounces_at_[hidden]> on behalf of Jayesh Badwaik via SG15 <sg15_at_[hidden]>
Sent: Monday, December 11, 2023 6:04:04 AM
To: sg15_at_[hidden] <sg15_at_[hidden]ocpp.org>
Cc: Jayesh Badwaik <jayesh_at_[hidden]>
Subject: Re: [SG15] Scheduling a virtual meeting to discuss where the std module source file should live

In my experience, it is not rare to get compiler from library package manager and would be an important use case. This is how a large community of HPC developers for example get their compilers (spack and easy build for example).

On Mon, 11 Dec 2023, 12:26 Mathias Stearn, <redbeard0531+isocpp_at_[hidden]<mailto:redbeard0531%2Bisocpp_at_[hidden]>> wrote:
Can we please be explicit about which kind of "package manager" is being referred to whenever we use that term? Are we talking about a system package manager (yum, apt, pacman, brew, winget etc) or a C++/library package manager (conan, vcpkg, cpm, etc)? This whole thread seems very ambiguous. I _think_ most people are talking about library package managers, but references to the FHS imply otherwise.

Right now it is very common to get a compiler and stdlib from the system package manager on linux. I think it is fairly rare right now to get the stdlib from a library package manager, although it would be nice if it were simple and easy to do so. To support std modules with the status quo environment, we need to work with system package managers. We will probably need to support other modules through them eventually, but it seems a both harder and a bit less urgent. The opposite seems to be the case for library package managers, where supporting non-std modules is probably a higher priority than the std module.

On Mon, Dec 11, 2023 at 7:27 AM Jayesh Badwaik via SG15 <sg15_at_[hidden]<mailto:sg15_at_[hidden]>> wrote:
I am not sure I get where this is coming from. The question is about being able to distribute and find a c++ compiler through a package manager.

In order to make things uniform, the posts also want system compiler to provide the same CPS interface.

Dependency would have been when it would have been necessary to install system compiler with a package manager.

On Mon, 11 Dec 2023, 00:57 Gabriel Dos Reis via SG15, <sg15_at_[hidden]<mailto:sg15_at_[hidden]>> wrote:
Are we establishing a package manager as a dependency for a C++ compiler (which typically is also the system compiler)?

-- Gaby

From: SG15 <sg15-bounces_at_[hidden]<mailto:sg15-bounces_at_[hidden]>> on behalf of Steve Downey via SG15 <sg15_at_[hidden]<mailto:sg15_at_[hidden]>>
Sent: Sunday, December 10, 2023 12:01:12 PM
To: Mark de Wever <koraq_at_xs4all.nl<mailto:koraq_at_[hidden]>>
Cc: Steve Downey <sdowney_at_[hidden]<mailto:sdowney_at_[hidden]>>; ISO C++ Tooling Study Group <sg15_at_[hidden]<mailto:sg15_at_[hidden]>>
Subject: Re: [SG15] Scheduling a virtual meeting to discuss where the std module source file should live

All the flags that make the BMI unusable make binaries unusable, in the general case. That standard libraries manage to avoid that is exceptional.

Package managers ought to be able to do this, and an install $prefix is the purview of a package manager. This is, of course, slightly to the side of where the interface is source lives.

But if a hello world project has to build the standard library, modules as a normal feature are DOA as a practical matter.

On Sun, Dec 10, 2023, 14:44 Mark de Wever <koraq_at_[hidden]<mailto:koraq_at_[hidden]>> wrote:
On Sun, Dec 10, 2023 at 11:40:59AM -0500, Steve Downey wrote:
> Does the std module use the same .a/.so as as headers?

Yes this is the library shipped by the vendor.

> How does that work with headers and -fno-exception, or does that have
> to be taken care of today by the user?

I'm not sure, I've no experience with systems where exceptions are
disabled. Most of libc++'s configuration options do not modify the
compilation flags.

> The other question is if the interface goes in include/ or share/libc++ for
> FHS like layout, and then is it possible to deploy a commonly used BMI into
> lib or libexec.

We don't want to deploy BMI files. In Clang BMI's have the same
limitations as precomiled headers; almost all compilation flags makes
BMIs incompatible. The build system needs to build the BMIs from the
module source files. For example, std.cppm.

> FHS implicitly assumes a coherent installation within a $prefix, which also
> means that ABI affecting flags are fixed, so system compilers ought to be
> able to at least pre build the system std modules.

At least for now that's not possible with Clang. I'm not sure whether it
ever be possible. For example, changing -std=c++xx flag changes the
exported named declarations of the module.

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Received on 2023-12-11 14:38:36