[openstack-dev] [all][requirements] a plan to stop syncing requirements into projects

Doug Hellmann doug at doughellmann.com
Thu Mar 15 23:29:37 UTC 2018

Excerpts from Matthew Thode's message of 2018-03-15 10:24:10 -0500:
> On 18-03-15 07:03:11, Doug Hellmann wrote:
> > What I Want to Do
> > -----------------
> > 
> > 1. Update the requirements-check test job to change the check for
> >    an exact match to be a check for compatibility with the
> >    upper-constraints.txt value.
> > 
> >    We would check the value for the dependency from upper-constraints.txt
> >    against the range of allowed values in the project. If the
> >    constraint version is compatible, the dependency range is OK.
> > 
> >    This rule means that in order to change the dependency settings
> >    for a project in a way that are incompatible with the constraint,
> >    the constraint (and probably the global requirements list) would
> >    have to be changed first in openstack/requirements. However, if
> >    the change to the dependency is still compatible with the
> >    constraint, no change would be needed in openstack/requirements.
> >    For example, if the global list constraints a library to X.Y.Z
> >    and a project lists X.Y.Z-2 as the minimum version but then needs
> >    to raise that because it needs a feature in X.Y.Z-1, it can do
> >    that with a single patch in-tree.
> > 
> I think what may be better is for global-requirements to become a
> gathering place for projects that requirements watches to have their
> smallest constrainted installable set defined in.
> Upper-constraints has a req of foo===2.0.3
> Project A has a req of foo>=1.0.0,!=1.6.0
> Project B has a req of foo>=1.4.0
> Global reqs would be updated with foo>=1.4.0,!=1.6.0
> Project C comes along and sets foo>=2.0.0
> Global reqs would be updated with foo>=2.0.0
> This would make global-reqs descriptive rather than prescriptive for
> versioning and would represent the 'true' version constraints of
> openstack.

It sounds like you're suggesting syncing in the other direction, which
could be useful. I think we can proceed with what I've described and
consider the work to build what you describe as a separate project.

> >    We also need to change requirements-check to look at the exclusions
> >    to ensure they all appear in the global-requirements.txt list
> >    (the local list needs to be a subset of the global list, but
> >    does not have to match it exactly). We can't have one project
> >    excluding a version that others do not, because we could then
> >    end up with a conflict with the upper constraints list that could
> >    wedge the gate as we had happen in the past.
> > 
> How would this happen when using constraints?  A project is not allowed
> to have a requirement that masks a constriant (and would be verified via
> the requirements-check job).

If project A excludes version X before the constraint list is updated to
use it, and then project B starts trying to depend on version X, they
become incompatible.

We need to continue to manage our declarations of incompatible versions
to ensure that the constraints list is a good list of versions to test
everything under.

> There's a failure mode not covered, a project could add a mask (!=) to
> their requirements before we update constraints.  The project that was
> passing the requirements-check job would then become incompatable.  This
> means that the requirements-check would need to be run for each
> changeset to catch this as soon as it happens, instead of running only
> on requirements changes.

I'm not clear on what you're describing here, but it sounds like a
variation of the failure modes that would be prevented if we require
exclusions to exist in the global list before they could be added to the
local list.

> >    We also need to verify that projects do not cap dependencies for
> >    the same reason. Caps prevent us from advancing to versions of
> >    dependencies that are "too new" and possibly incompatible. We
> >    can manage caps in the global requirements list, which would
> >    cause that list to calculate the constraints correctly.
> > 
> >    This change would immediately allow all projects currently
> >    following the global requirements lists to specify different
> >    lower bounds from that global list, as long as those lower bounds
> >    still allow the dependencies to be co-installable. (The upper
> >    bounds, managed through the upper-constraints.txt list, would
> >    still be built by selecting the newest compatible version because
> >    that is how pip's dependency resolver works.)
> > 
> > 2. We should stop syncing dependencies by turning off the
> >    propose-update-requirements job entirely.
> > 
> >    Turning off the job will stop the bot from proposing more
> >    dependency updates to projects.
> > 
> >    As part of deleting the job we can also remove the "requirements"
> >    case from playbooks/proposal/propose_update.sh, since it won't
> >    need that logic any more. We can also remove the update-requirements
> >    command from the openstack/requirements repository, since that
> >    is the tool that generates the updated list and it won't be
> >    needed if we aren't proposing updates any more.
> > 
> > 3. Remove the minimum specifications from the global requirements
> >    list to make clear that the global list is no longer expressing
> >    minimums.
> > 
> >    This clean-up step has been a bit more controversial among the
> >    requirements team, but I think it is a key piece. As the minimum
> >    versions of dependencies diverge within projects, there will no
> >    longer *be* a real global set of minimum values. Tracking a list of
> >    "highest minimums", would either require rebuilding the list from the
> >    settings in all projects, or requiring two patches to change the
> >    minimum version of a dependency within a project.
> > 
> >    Maintaining a global list of minimums also implies that we
> >    consider it OK to run OpenStack as a whole with that list. This
> >    message conflicts with the message we've been sending about the
> >    upper constraints list since that was established, which is that
> >    we have a known good list of versions and deploying all of
> >    OpenStack with different versions of those dependencies is
> >    untested.
> > 
> As noted above I think that gathering the min versions/maskings from
> openstack projects to be valuable (especially to packagers who already
> use our likely invalid values already).

OK. I don't feel that strongly about the cleanup work, so if we want to
keep the lower bounds in place I think that's OK.

> > After these 3 steps are done, the requirements team will continue
> > to maintain the global-requirements.txt and upper-constraints.txt
> > files, as before. Adding a new dependency to a project will still
> > involve a review step to add it to the global list so we can monitor
> > licensing, duplication, python 3 support, etc. But adjusting the
> > version numbers once that dependency is in the global list will be
> > easier.
> > 
> Thanks for writing this up, I think it looks good in general, but like
> you mentioned before, there is some discussion to be had about gathering
> and creating a versionspec from all of openstack for requirements.

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