The st_commits and st_diffs columns on merge_request_diffs historically held the
YAML-serialised data for a merge request diff, in a variety of formats.
Since 9.5, these have been migrated in the background to two new tables:
merge_request_diff_commits and merge_request_diff_files. That has the advantage
that we can actually query the data (for instance, to find out how many commits
we've stored), and that it can't be in a variety of formats, but must match the
new schema.
This is the final step of that journey, where we drop those columns and remove
all references to them. This is a breaking change to the importer, because we
can no longer import diffs created in the old format, and we cannot guarantee
the export will be in the new format unless it was generated after this commit.
This finishes the procedure for migrating events from the old format
into the new format. Code no longer uses the old setup and the database
tables used during the migration process are swapped, with the old table
being dropped.
While the database migration can be reversed this will 1) take a lot of
time as data has to be coped around 2) won't restore data in the
"events.data" column as we have no way of restoring this.
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/37241
Migrations shouldn't fail RuboCop checks - especially lint checks, such
as the nested method check. To avoid changing code in existing
migrations, add the magic comment to the top of each of them to skip
that file.
