[LLVMdev] [RFC] Developer Policy for LLVM C API

[Hal Finkel]

----- Original Message -----
> From: "David Majnemer" <david.majnemer at gmail.com>
> To: "Eric Christopher" <echristo at gmail.com>
> Cc: "Lang Hames" <lhames at apple.com>, "LLVM Dev" <llvmdev at cs.uiuc.edu>
> Sent: Friday, July 17, 2015 7:11:57 PM
> Subject: Re: [LLVMdev] [RFC] Developer Policy for LLVM C API
> 
> On Fri, Jul 17, 2015 at 3:41 PM, Eric Christopher <
> echristo at gmail.com > wrote:
> 
> 
> 
> Hi Juergen,
> 
> 
> I've actually got another, perhaps more radical, plan. Let's just get
> rid of the C API or move it to another project. This simplifies a
> lot of the plans here where people have too many different ideas of
> how the C API should work.
> 
> 
> At this point the people who want a stable C API per incremental
> version can do that and handle the overhead of porting themselves
> and the people that want a C API that just happens to be a C
> interface can have a wrapper (or SWIG or whatever they want).
> 
> 
> I realize it's radical, but it seems that there are so many different
> wants for C API here that solving everyone's problems or wants is
> going to be impossible.
> 
> 
> I am strongly in favor of moving the bindings, C or otherwise, to
> another project.

I agree. From my viewpoint we have two primary problems with the C API:

 1. Many of the LLVM contributors don't use it, and thus, don't have a great understanding of how it can be most-usefully updated/improved, and what functionality needs to be exposed. We have most, but not all, transformations; many, but not all, IR features, etc.

 2. We don't have a good set of tests for it, nor do we have a good set of tutorials/documentation for it. Our tutorials, specifically, are in C++, not in C. We could break the C API and we'd likely remain unaware for quite awhile.

Putting it in a separate project will force those who have a stake in its existence to take the responsibility of moving it forward. Separate project, or not, however, we should have a better developer policy regarding the C API (and the other bindings) that fall under the LLVM umbrella. Specifically, we should outline what features need to be exposed, and we should actively maintain (and test for) full coverage of those features.

 -Hal

> 
> -eric
> 
> 
> 
> On Fri, Jul 17, 2015 at 12:39 PM Juergen Ributzka < juergen at apple.com
> > wrote:
> 
> 
> Hi @ll,
> 
> a few of us had recently a discussion about how to manage the C API
> and possible policies regarding addition, maintenance, deprecation,
> and removal of API.
> 
> Even thought there is a strong agreement in the community that we
> shouldn't break released C API and should be backwards compatible,
> there doesn’t seem to be a developer policy that backs that up. This
> is something we should fix.
> 
> I was wondering what the interested parties think of the current
> approach and what could/should we improve to make the use and
> maintenance of the C API easier for users and the developers alike.
> 
> I was hoping we could also introduce a process that allows the
> removal of an API after it has been deprecated for a whole release
> and the release notes stated that it will be removed.
> 
> Thoughts? Comments?
> 
> Cheers,
> Juergen
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-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory