[LLVMdev] Project Release Branches

[John Criswell]

On 11/12/12 5:22 PM, 32bitmicro wrote:
> John,
>
>> Dear Pawel and All,
>>
>> Pawel (and other release managers), can you ask the project maintainers
>> for each project whether they want a release branch before creating it
>> next time?  Alternatively, can you leave branch creation up to the
>> project maintainers as in the past?
>   I think asking project maintainers for a go/no-go for branch creation
> is a very good idea that should be incorporated into the LLVM release
> process.

What I think needs to be done is to add details like this to the 
document describing the release management process.  In the past, the 
release manager has just sort of known what to branch and what not to 
branch.  I can see how that information fails to transmit between 
release managers.
:)

In the past, I recall the release manager made branches of LLVM, Clang, 
and test-suite because all 3 of those projects followed LLVM mainline.  
Other projects simply followed whatever branching policy they wanted.

>
>> Pawel, you created a release_32 branch of SAFECode last night without my
>> consultation.  That commit itself is fine since we just happen to be
>> tracking LLVM mainline right now; I'll just tell SAFECode developers to
>> move development to the release_32 branch. However, in general, you
>> can't assume that SAFECode mainline is tracking LLVM mainline; if you
>> do, and we're not, you may fork a release branch before all changes to
>> the previous release branch have been folded back into mainline.
>>
>   John, it was not my intention to disrupt your work in any way.
> However, branching for release is a bit of a grey area and I
> have made a judgment call to branch SAFECode in sync with llvm.
> This could have been a bit overzealous but I am used to
> "release at any time" approach or agile project management.
>
>   Since LLVM/Clang has grown so much I think the release process
> will require some adjustment to keep up with the sheer size of it.
>  From my experience it is hard to make progress without accepting
> changes while at the same time making changes usually leads to
> some unintentional breakages.

Okay.  Just know that SAFECode is undergoing evaluation by one of our 
funding agencies.  There have been and will be times in which we can't 
tolerate breakage.  Fortunately, the next evaluation is about 12 months 
away, IIRC.

>
>   As for the SAFECode, perhaps I have made assumptions
> on how you track mainline that are not valid.
> It would be constructive to have your perspective on how
> to manage release of a project dependent on the LLVM.

I think there are two general ways to do it:

1) When someone makes a change to LLVM that breaks the C++ API, they 
make the corresponding changes to a set of projects that opt-in.  I 
would certainly love that for SAFECode; one of the reasons why we 
sometimes opt not to track mainline is because the C++ API is simply too 
volatile.

If the community helped us track mainline, then having the release 
manager branch the opted-in projects makes a lot of sense.

2) If people aren't going to update projects consistently when C++ API 
changes are made, then the only thing that the release manager should 
branch is LLVM, Clang, test-suite, and any project that commits to 
tracking LLVM mainline.  Every other project is on its own.

I would love it if option #1 were adopted, but I'm skeptical if the LLVM 
community as a whole is interested in fixing up sub-projects when the 
main projects make changes.  However, if my skepticism is misplaced, 
please let me know.
:)

So, assuming no changes in C++ API change policy, I'd prefer to make 
SAFECode branches myself.  I'd rather focus on SAFECode development than 
chasing LLVM's tail, so I don't think we can guarantee that our mainline 
development is always going to track LLVM's.

-- John T.