Constants should always be only assigned once. The logical OR assignment
of a constant is a relic of the past before we used zeitwerk for
autoloading and had bugs where a file could be loaded twice resulting in
constant redefinition warnings.
Having a large number of post-deploy migrations running out-of-numerical-sequence with pre-deploy migrations can be problematic. For example, if we have the sequence
- db/migrate/2017... - add column
- db/post_migrate/2018... - drop the column
- db/migrate/2021... - add the same column again
It will work fine in numerical order. But if you run the pre-deploy migrations **followed by** the post-deploy migrations, you will not get the same result.
Our post-deploy system is designed to allow for seamless upgrades of Discourse. However, it is reasonable for us to only support this totally seamless experience for a limited period of time. This commit moves all post_deploy migrations which are more than 1 year old (i.e. more than 2 major Discourse versions ago) into the regular pre-deploy migrations directory. This limits the impact of any edge cases caused by out-of-numerical-sequence migrations.
