[GHC DevOps Group] State of CI

[Boespflug, Mathieu]

Hi Simon,

On 6 June 2018 at 11:11, Simon Marlow <marlowsd at gmail.com> wrote:
> On 6 June 2018 at 09:21, Boespflug, Mathieu <m at tweag.io> wrote:
>
> [...]
>
>> * Our GitHub lock-in factor is currently low to pretty much absent,
>> and would remain low even if the review workflow becomes more
>> systematically GitHub centric (it already is for some small
>> contributions).
>> * That's because tickets remain on Trac, and the code along with the
>> entirety of its history remains in a standard Git repository, GitHub
>> or not. Also because GitHub is not a CI provider, those providers we
>> do use integrate with other code hosting solutions (e.g. Appveyor with
>> GitLab), and the surface area of CI provider-specific code is small.
>
>
> We should keep in mind, though, is that past code reviews is valuable
> content that we can't discard, nor can we easily migrate it to a different
> code review platform. At this point we have nearly 5K diffs on Phabricator,
> many of which have non-trivial code-review trails, and these are
> cross-referenced from Trac, emails, and other places.

Indeed. And this is AFAICS the only main "lock-in factor", in that
reviews on GitHub pull requests is the only "GitHub native" state. All
other long term state (code, code history, tickets, code reviews) is
stored elsewhere.

We already use GitHub for some code reviews. If we moved elsewhere
exclusively someday, then we'd mark the github.com/ghc/ghc repo as
"archived". This would make it a read-only copy available forever in
the future, meaning that all existing links in the GHC codebase or
elsewhere would continue to work. New code reviews would happen
elsewhere, no history would be lost and cross referencing would work
as it did before.

So if we moved e.g. from Phabricator to GitHub exclusively, then we'd
do the same thing. Retain Phabricator as-is, just don't add new code
reviews to it.

Not that this changes anything to the plan of record regarding CI.
Topic for a separate thread I guess.