[Fedora-packaging] llvm case study: yum's handling of newly-converted noarch subpackages

[Michel Alexandre Salim]

An LLVM user reported to me a problem updating LLVM (from the version
in F13-updates to the version that is then in Koji), and I suggested
that he filed a bug report.

https://bugzilla.redhat.com/show_bug.cgi?id=600969

In the discussion that follows, James Antill diagnosed the problem as
due to llvm-doc being changed to be a noarch subpackage, as supported
by RPM 4.7 and above, and thus when using yum to update from
llvm-2.7-1 (with arched -doc) to 2.7-4 (noarch doc), llvm-2.7-1 causes
llvm-2.7-1.i686 to be pulled in to satisfy the dependencies)

To reproduce:
- on an x86_64 system, yum install llvm-doc
- Download llvm{,-doc} from Koji
http://koji.fedoraproject.org/koji/buildinfo?buildID=176782
- Try a yum localupdate or a yum localinstall

The suggested fix by James, and by some folks on #fedora-devel, is to
make the new -doc Obsoletes: the old doc. This, alas, does not quite
work:


http://koji.fedoraproject.org/koji/taskinfo?taskID=2236690

- Download llvm-2.7-5 from the scratch builds above
- Retry localupdate / localinstall

the -doc update is considered but then dropped.

Any idea how to fix this? We should probably add a section to the
packaging guidelines, on how to migrate to noarch subpackages without
breaking upgrade paths.

Thanks,

-- 
Michel Alexandre Salim
Fedora Project Contributor: http://fedoraproject.org/

Email:  salimma at fedoraproject.org  | GPG key ID: 78884778
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