The error messages from this failing seem mysterious - do we need to improve the directive to return clearer messages, or even do basic error checking for this sort of duplication?

I don't think you can (reasonably simple) distinguish this error from a case where the user has explicitly written a duplicate redirect.

Let's just fix this and get on with life. If it happens more often inn the future we can always rethink whether we find a better solution.

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout v3.6.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 afa863301c25a96e9773914274c38eaa1087c9e5

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #24795: DOC: Fix duplicate redirect'

4. Push to a named branch:

git push YOURFORK v3.6.x:auto-backport-of-pr-24795-on-v3.6.x

5. Create a PR against branch v3.6.x, I would have named this PR:

"Backport PR #24795 on branch v3.6.x (DOC: Fix duplicate redirect)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout v3.6.2-doc
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 afa863301c25a96e9773914274c38eaa1087c9e5

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #24795: DOC: Fix duplicate redirect'

4. Push to a named branch:

git push YOURFORK v3.6.2-doc:auto-backport-of-pr-24795-on-v3.6.2-doc

5. Create a PR against branch v3.6.2-doc, I would have named this PR:

"Backport PR #24795 on branch v3.6.2-doc (DOC: Fix duplicate redirect)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.

If there are merge conflicts, we likely do not need to backport.