[chore] migration to update `statuses.thread_id` to be notnull (#4160)

# Description

This is quite a complex database migration that updates the `statuses.thread_id` column to be notnull, in order that statuses always be threaded, which will be useful in various pieces of upcoming work. This is unfortunately a migration that acts over the entire statuses table, and is quite complex in order to ensure that all existing statuses get correctly threaded together, and where possible fix any issues of statuses in the same thread having incorrect thread_ids.

TODO:
- ~~update testrig models to all be threaded~~
- ~~update code to ensure thread_id is always set~~
- ~~run on **a copy** of an sqlite production database~~
- ~~run on **a copy** of a postgres production database~~

## Checklist

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [ ] I/we have made any necessary changes to documentation.
- [x] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4160
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

1 files changed, 0 insertions, 44 deletions

diff --git a/internal/processing/status/create.go b/internal/processing/status/create.go
index 23189411a..f9f986256 100644
--- a/internal/processing/status/create.go
+++ b/internal/processing/status/create.go
@@ -217,10 +217,6 @@ func (p *Processor) Create(
 		return nil, errWithCode
 	}
 
-	if errWithCode := p.processThreadID(ctx, status); errWithCode != nil {
-		return nil, errWithCode
-	}
-
 	// Process the incoming created status visibility.
 	processVisibility(form, requester.Settings.Privacy, status)
 
@@ -444,46 +440,6 @@ func (p *Processor) processInReplyTo(
 	return nil
 }
 
-func (p *Processor) processThreadID(ctx context.Context, status *gtsmodel.Status) gtserror.WithCode {
-	// Status takes the thread ID of
-	// whatever it replies to, if set.
-	//
-	// Might not be set if status is local
-	// and replies to a remote status that
-	// doesn't have a thread ID yet.
-	//
-	// If so, we can just thread from this
-	// status onwards instead, since this
-	// is where the relevant part of the
-	// thread starts, from the perspective
-	// of our instance at least.
-	if status.InReplyTo != nil &&
-		status.InReplyTo.ThreadID != "" {
-		// Just inherit threadID from parent.
-		status.ThreadID = status.InReplyTo.ThreadID
-		return nil
-	}
-
-	// Mark new thread (or threaded
-	// subsection) starting from here.
-	threadID := id.NewULID()
-	if err := p.state.DB.PutThread(
-		ctx,
-		&gtsmodel.Thread{
-			ID: threadID,
-		},
-	); err != nil {
-		err := gtserror.Newf("error inserting new thread in db: %w", err)
-		return gtserror.NewErrorInternalError(err)
-	}
-
-	// Future replies to this status
-	// (if any) will inherit this thread ID.
-	status.ThreadID = threadID
-
-	return nil
-}
-
 func processVisibility(
 	form *apimodel.StatusCreateRequest,
 	accountDefaultVis gtsmodel.Visibility,