Race condition in the diff.yml workflow

[gouttegd]

The diff.yml workflow (aka the gogoeditdiff workflow) automatically runs whenever someone comments on a PR, to check whether the comment includes the keyword #gogoeditdiff -- if that’s the case, then the workflows goes on to generate a diff of the ontology between the current master branch and the PR’s branch.

Some steps in that workflow critically require the PR to be in the open state to work -- if the PR is closed (whether it is because it has been merged or, on the contrary, rejected), they fail loudly with a Cannot read properties of null (reading 'name') error.

To prevent this error from happening, there is already a guard rail in place (#3437) that ensures the workflow only runs on non-closed PR.

Unfortunately, that’s not enough. If someone writes a comment and then almost immediately after closes the PR, the diff workflow will still be triggered as soon as the comment is written, but by the time the execution flow reaches the comment-branch step, the PR will be closed and the step will loudly fail.

This has happened for example on PR #3469, where I added this comment and almost immediately merged (and so, closed) the PR, resulting in this failure of the diff.yml workflow.

Not sure what we can do here -- testing that the target PR is not closed is of no use (we are already doing that, but it does not catch the fact that the PR might be closed shortly after the workflow has started).