Fedora 33 System-Wide Change proposal: Boost 1.73 upgrade

[Ben Cotton]

https://fedoraproject.org/wiki/Changes/F33Boost173

== Summary ==
This change brings Boost 1.73 to Fedora. This will mean Fedora ships with a
recent upstream Boost release.

== Owner ==

* Name: [[User:jwakely| Jonathan Wakely]]
* Email: jwakely(a)redhat.com

== Detailed Description ==

The aim is to synchronize Fedora with the most recent Boost release.
Because ABI stability is one of explicit Boost non-goals, this entails
rebuilding of all dependent packages. This has also always entailed yours
truly assisting maintainers of client packages in decoding cryptic
boost-ese seen in output from g++. Such care is to be expected this time
around as well.

The equivalent changes for previous releases were
[[Changes/F30Boost169|Fedora 30 Change]], [[Changes/F29Boost167|Fedora 29
Change]], [[Changes/F28Boost166|Fedora 28 Change]],
[[Changes/F27Boost164|Fedora 27 Change]], [[Changes/F26Boost163|Fedora 26
Change]], [[Changes/F25Boost161|Fedora 25 Change]],
[[Changes/F24Boost160|Fedora 24 Change]],  [[Changes/F23Boost159|Fedora 23
Change]] and [[Changes/F22Boost158|Fedora 22 Change]].

== Benefit to Fedora ==

Fedora 32 includes Boost 1.69 which is the same version as F31 and F30, and
is several releases behind the latest upstream release (Boost 1.73 is due
for release late April 2020).

Fedora will stay relevant, as far as Boost clients are concerned. Boost
1.73 brings four new components:
* [https://www.boost.org/libs/outcome/ Boost.Outcome], A set of tools for
reporting and handling function failures in contexts where <i>directly</i>
using C++ exception handling is unsuitable, from Niall Douglas.
* [https://www.boost.org/libs/histogram/ Boost.Histogram], Fast and
extensible multi-dimensional histograms with convenient interface for
C++14, from Hans Dembinski.
* [https://www.boost.org/libs/variant2/ Boost.Variant2], A never-valueless,
strong guarantee implementation of std::variant, from Peter Dimov.
* [https://www.boost.org/libs/nowide/ Boost.Nowide], Standard library
functions with UTF-8 API on Windows, from Artyom Beilis.
* [https://www.boost.org/libs/static_string/ Boost.StaticString], A
dynamically resizable string of characters with compile-time fixed capacity
and contiguous embedded storage, from Vinnie Falco and Krystian Stasiowski.

== Scope ==
* Proposal owners:
** Build will be done with Boost.Build v2 (which is the upstream-sanctioned
way of building Boost)
** Request a "f33-boost" [
https://docs.pagure.org/releng/sop_adding_side_build_targets.html build
system tag] ([
http://lists.fedoraproject.org/pipermail/devel/2011-November/159908.html
discussion]): TODO
** Build boost into that tag (take a look at the [
http://koji.fedoraproject.org/koji/buildinfo?buildID=606493 build #606493]
for inspiration)
** Post a request for rebuilds to fedora-devel
** Work on rebuilding dependent packages in the tag.
** When most is done, re-tag all the packages to rawhide
** Watch fedora-devel and assist in rebuilding broken Boost clients (by
fixing the client, or Boost).

* Other developers:
** Those who depend on Boost DSOs will have to rebuild their packages.
Feature owners will alleviate some of this work as indicated above, and
will assist those whose packages fail to build in debugging them.
** The existing `boost-nowide` package will need to be retired, as it is
now included in the upstream Boost release.


* Release engineering: [https://pagure.io/releng/issue/9421 #9421] (a check
of an impact with Release Engineering is needed)

* Policies and guidelines:
** Apart from scope, this is business as usual, so no new policies, no new
guidelines.

* Trademark approval: N/A (not needed for this Change)


== Upgrade/compatibility impact ==
* The `boost-jam` package has been replaced by `boost-b2`. The separate
`boost-nowide` package will be replace by a subpackage of `boost`.
* No manual configuration or data migration needed.
* Some impact on other packages needing code changes to rebuild.
Historically this hasn't been too much of a problem and could always be
resolved before deadline.

== How To Test ==
* No special hardware is needed.
* Integration testing simply consists of installing Boost packages (`dnf
install boost`) on Fedora and checking that it does not break other
packages (see below for a way to obtain a list of boost clients).


== User Experience ==
* Expected to remain largely the same.
* Developers building third-party software on Fedora may need to rebuild
against the new Boost packages, and may need to adjust their code if the
new Boost release is not source-compatible.
* Developers using `bjam` to build their own software will need to switch
to using the new name for the tool, `b2`

== Dependencies ==
Packages that must be rebuilt:
<code>$ dnf repoquery -s --releasever=rawhide --whatrequires libboost\*
--disablerepo=* --enablerepo=fedora | sort -u</code>

All clients:
<code>$ dnf repoquery --releasever=rawhide --archlist=src --whatrequires
boost-devel --disablerepo='*' --enablerepo=fedora-source</code>

== Contingency Plan ==

* Contingency mechanism: Worst case scenario is to abandon the update and
simply ship F33 with Boost 1.69, which is already in rawhide. It would also
be possible to ship an older release (1.70.0, 1.71.0 or 1.72.0) which would
still be newer than in current Fedora releases.

* Contingency deadline: We will know whether the change can be made once
the rebuilds in the side tag are done, which will be July 2020, ideally
before the mass rebuild.

* Blocks release? No
* Blocks product? None


== Documentation ==
* https://www.boost.org/users/history/version_1_73_0.html (Beta1 released
on 12 April 2020, final release expected soon)
* https://www.boost.org/users/history/version_1_72_0.html (released on 11
December 2019)
* https://www.boost.org/users/history/version_1_71_0.html (released on 19
August 2019)
* https://www.boost.org/users/history/version_1_70_0.html (released on 12
April 2019)
* https://www.boost.org/development/index.html

== Release Notes ==
Boost has been upgraded to version 1.73. Apart from a number of bug fixes
and improvements to existing libraries. Compared to Fedora 32, this brings:
* New header-only components: [https://www.boost.org/libs/outcome/
Boost.Outcome], [https://www.boost.org/libs/histogram/ Boost.Histogram], [
https://www.boost.org/libs/variant2/ Boost.Variant2], [
https://www.boost.org/libs/nowide/ Boost.Nowide] and [
https://www.boost.org/libs/static_string/ Boost.StaticString].
* The `bjam` tool in the `boost-jam` package has been replaced by `b2` in
the `boost-b2` package.

-- 
Ben Cotton
He / Him / His
Senior Program Manager, Fedora & CentOS Stream
Red Hat
TZ=America/Indiana/Indianapolis