Error 500 when moving posts

zogstrip · June 19, 2026, 5:50pm

@here there’s a 55% chance this will fix the issue

github.com/discourse/discourse-activity-pub

FIX: Reuse a topic's tombstoned collection when moving posts in (#319)

main ← fix/move-posts-tombstoned-collection

merged 07:00PM - 19 Jun 26 UTC

ZogStriP

+184 -294

### What Moving one or more posts into a `full_topic` topic could raise `Active…Record::RecordNotUnique` and surface to the user as an HTTP 500 — from core's `TopicsController#move_posts`, which only rescues `RecordInvalid` / `RecordNotSaved`, so anything else becomes a 500. Reported on Meta: https://meta.discourse.org/t/error-500-when-moving-posts/397654 ### Why ActivityPub records are hidden once tombstoned, via `IdentifierValidations`' `default_scope { where.not(ap_type: Tombstone.type) }`. The row still exists, though, and still occupies the unique `(model_type, model_id)` index (`unique_activity_pub_collection_models`). The `:first_post_moved` / `:post_moved` handlers check `!topic.activity_pub_object` — which the default scope reports as `nil` for a tombstoned collection — and call `create_activity_pub_collection!`, which blindly inserts a second collection for the same topic and collides on the unique index. It's data-dependent (the destination topic's collection must have been tombstoned previously, e.g. via a delete/restore cycle), which matches the intermittent, "no visible preconditions" reports. ### How `create_activity_pub_collection!` now looks the collection up `unscoped`, restores it when tombstoned, and reuses it instead of inserting a duplicate. This makes the method idempotent for all of its callers, and preserves the collection's `ap_id` (its federation identity) rather than orphaning it. ### Tests - Adds a regression test for moving posts into a topic whose collection was tombstoned. - A second commit simplifies the `move_posts` topic specs — collapsing the per-scenario example fan-out into one example each, with `:aggregate_failures` on the group. Same coverage, 38 → 14 examples, roughly half the runtime.

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Error 500 when moving posts

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