[llvm-dev] RFC: Update LLVM_VERSION_SUFFIX CMake variable for release candidates

Harald van Dijk via llvm-dev
Thu, 01 Jul 2021 16:18:04 -0000

On 29/06/2021 18:39, Tom Stellard via llvm-dev wrote:
> Hi,
>
> I would like to propose that we start using the LLVM_VERSION_SUFFIX
> CMake variable for release candidates.  For example:
> after the release/13.x branch is created, instead of changing
> LLVM_VERSION_SUFFIX from "git" to "", we would change
it to "rc1",
> then after the 13.0.0-rc1 release is tagged, we would update the
> variable to "rc2", etc. Then right before the final release has
been
> tagged, we would set it to ""
> The library SONAME's currently include LLVM_VERSION_SUFFIX, so this
> change will cause each release candidate to have a different SONAME
> for libraries.  This is correct for X.Y.0 releases, since it's possible
> for a library's ABI to change between release candidates.  However,
> for X.Y.1 releases, we do not want to modify the SONAME's at all, so
> the build system will need to be updated to accommodate this change.

This would mean that the so-called release candidate is no longer a
candidate for release. Even if no problems are identified in 13.0.0-rc1,
it is still guaranteed that 13.0.0 will be different from 13.0.0-rc1. In
particular, this means if a distro were to do a rebuild against
13.0.0-rc1, and then no further changes are needed and 13.0.0 can be
released, the distro will still need to rebuild everything that was
already built against 13.0.0-rc1 against 13.0.0. The fact that the
SONAME changes also means it's possible that other projects adjust to
wrongly account for the SONAME change in a way that happens to work for
the release candidates, but not for the actual release, so testing with
the release candidate suggests that everything is fine when in fact it
isn't.

I was working on changing my own testing procedures for my own system to
handle the current release candidate structure, where I am in much the
same boat as distros, except on a smaller scale. Currently,
llvm-12.0.0rc5.src.tar.xz and llvm-12.0.0.src.tar.xz are different
files, but the only difference is that the former extracts to an
llvm-12.0.0rc5.src directory whereas the latter extracts to a
llvm-12.0.0.src directory, the archives are otherwise 100% identical,
down to the mtime of each individual file. I wanted to use this to
create a build of LLVM+clang 12.0.1-rc3 that, if 12.0.1-rc3 turns out to
be the final release candidate, will be bitwise identical to the same
build of LLVM+clang 12.0.1 and there will be no reason to re-test
anything that worked with 12.0.1-rc3 against 12.0.1, allowing me to
avoid a further mass rebuild once 12.0.1 is released. Under your
proposed scheme, this may continue to work for x.0.1 releases, I am not
sure whether it would continue to work for x.1.0 releases, but it would
definitely cease to be an option for x.0.0 releases. That seems a shame,
because it means the release candidates will be less tested than they
would otherwise be.

Cheers,
Harald van Dijk