Fix "list index out of range" error

[jo-so]

Fixes #4842

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file
• Pull request includes a sign off

Signed-off-by: Jörg Sommer <[email protected]>

[anoadragon453]

Hello! Before review you'll need to add a changelog entry as per https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.rst#changelog. Thanks!

[jo-so]

Hello! Before review you'll need to add a changelog entry as per https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.rst#changelog. Thanks!

And if the review gives a NACK?

The process of

1. creating a commit
2. push the branch
3. create a pull-request
4. create a doc-commit with the PR number
5. repush the branch
6. get a review which NACKs the PR or requests changes
7. redo the doc stuff
   is really not handy, nor gives any appeal to do it.

[anoadragon453]

@jo-so Fair enough.

[anoadragon453]

To me it sounds like the error in #4842 was due to batch.events being an empty list, rather than None. In that case, this if statement would still run and crash.

Instead you may want to check if len(batch.events) > 0.

[jo-so]

I'm not a Python expert. I found https://stackoverflow.com/questions/53513/how-do-i-check-if-a-list-is-empty

[richvdh]

Hello! Before review you'll need to add a changelog entry as per https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.rst#changelog. Thanks!

And if the review gives a NACK?

... then you update your PR accordingly.

The process of

1. creating a commit
2. push the branch
3. create a pull-request
4. create a doc-commit with the PR number
5. repush the branch

you might find something like this useful to get the next PR number, so you can create the news file before pushing:

curl -s "https://api.github.com/repos/matrix-org/synapse/issues?state=all&per_page=1" | jq -r ".[0].number + 1"

Obviously it assumes you create the PR before any more issues or PRs are opened, but in general it will save time.

6. get a review which NACKs the PR or requests changes
7. redo the doc stuff

There is no need to redo the news file when updating a PR.

is really not handy, nor gives any appeal to do it.

I understand that it's not particularly convenient, but ultimately we struggle to handle the number of PRs we get as it is. Anything that contributors can do to make the job easier is much appreciated by us.

On which note, please ensure that your PRs contain a link to the bug that they are fixing in the body of the PR description. Github does not link to issues when the issue number is only in the title of the PR.

[richvdh]

please create the changelog file so that the CI runs

[richvdh]

I'm not quite sure if this is the right solution. On hold pending further information at #4842 (comment).

[richvdh]

I don't think this change is correct, and as per #4842 it's unclear what we're trying to fix anyway, so I'm going to close this for now.