[gdal-dev] github backporting application

[Nyall Dawson]

On Mon, 18 Mar 2019 at 09:06, Even Rouault <even.rouault at spatialys.com> wrote:
>
> Hi,
>
> I've just seen that QGIS has started using a github backporting application,
> https://github.com/apps/backporting, and I've just setup it for GDAL and PROJ
>
> So the workflow is :
> 1) Create a pull request against master
> 2) If backport is needed, label it with "backport {branchname}" (I've created
> a "backport release/2.4" for GDAL and "backport 6.0" for PROJ)
> 3) Merge the pull request
> 4) The backport application automatically creates a new pull request against
> the target backport branch, and cherry-picks all the commits of the original
> pull request
> 5) Wait for CI to complete (or not) and merge (or not) this new PR
>
> Of course this doesn't solve automagically conflicts etc, but can be
> convenient for trivial backports when branches are close enough

Just from a QGIS developer's perspective:

The system is working OK, but there's two current limitations in the
bot which make it difficult to work within nicely:

1. Backported PRs have a generic name, e.g. "Backport #9528"
(https://github.com/qgis/QGIS/pull/9531). This makes it hard to see
what outstanding backports are open without diving into the details of
each. There's a fix here for the bot, but not merged yet:
https://github.com/tibdex/backport/pull/19 . On a similar vein, the
backported PRs don't include original author information, which in my
view makes reviewing a bit harder (since we have policies in place
that require a review from a different developer to the original
submitter for backports to the stable branch. Not a blocker, but just
opens the policy for easier abuse).

2. It's hard to track multiple backports, because currently the bot
only supports a single branch. See
https://github.com/tibdex/backport/pull/18 . We have to currently
"step" the backports back through multiple branches individually by
tagging the first auto created backport with the next branch to
backport to. Hopefully Matthias' PR is merged soon and fixes this
situation, but in the meantime it's fragile and potentially a backport
could accidently be skipped for a branch.

Nyall