Fix OrphanedInviteTokensCleanup migration

Some database schemas have `members.created_at` set as `timestamp with
time zone`, while on GitLab.com and dev we have `timestamp without time
zone`. If the column has a time zone, the `OrphanedInviteTokensCleanup`
migration fails with the following error:

```
PG::InvalidObjectDefinition: ERROR: functions in index predicate must be
marked IMMUTABLE
```

As described in https://stackoverflow.com/a/58848792, if the time zone
depends on the server, the result might change if somebody changes the
time zone. We need to lock the time zone if the timezone depends on the
server.

We need to make sure the comparison between `created_at` and
`invite_accepted_at` are done using the same types or PostgreSQL will
reject the query due to immutability concerns. Calling `TIMEZONE('UTC',
column)` on a `timestamp without time zone` converts it to `timestamp
with time zone` type. Calling the same function on a `timestamp with
time zone` converts it to a type of `timestamp without time
zone`. Therefore, we should check the type before we do this conversion.

There is an epic that deals with reconciling these datetime with
timezone differences: https://gitlab.com/groups/gitlab-org/-/epics/2473

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/339091

Changelog: fixed

db/post_migrate/20210809123658_orphaned_invite_tokens_cleanup.rb

@@ -6,15 +6,12 @@ class OrphanedInviteTokensCleanup < ActiveRecord::Migration[6.1]
   disable_ddl_transaction!
 
   TMP_INDEX_NAME = 'tmp_idx_orphaned_invite_tokens'
-  QUERY_CONDITION = "invite_token IS NOT NULL and invite_accepted_at IS NOT NULL and invite_accepted_at < created_at"
 
   def up
-    membership = define_batchable_model('members')
+    add_concurrent_index('members', :id, where: query_condition, name: TMP_INDEX_NAME)
 
-    add_concurrent_index('members', :id, where: QUERY_CONDITION, name: TMP_INDEX_NAME)
-
-    membership.where(QUERY_CONDITION).pluck(:id).each_slice(10) do |group|
-      membership.where(id: group).where(QUERY_CONDITION).update_all(invite_token: nil)
+    membership.where(query_condition).pluck(:id).each_slice(10) do |group|
+      membership.where(id: group).where(query_condition).update_all(invite_token: nil)
     end
 
     remove_concurrent_index_by_name('members', TMP_INDEX_NAME)
@@ -25,4 +22,30 @@ class OrphanedInviteTokensCleanup < ActiveRecord::Migration[6.1]
 
     # This migration is irreversible
   end
+
+  private
+
+  def membership
+    @membership ||= define_batchable_model('members')
+  end
+
+  # We need to ensure we're comparing timestamp with time zones across
+  # the board since that is an immutable comparison. Some database
+  # schemas have a mix of timestamp without time zones and and timestamp
+  # with time zones: https://gitlab.com/groups/gitlab-org/-/epics/2473
+  def query_condition
+    "invite_token IS NOT NULL and invite_accepted_at IS NOT NULL and #{timestamptz("invite_accepted_at")} < #{timestamptz("created_at")}"
+  end
+
+  def timestamptz(name)
+    if column_type(name) == "timestamp without time zone"
+      "TIMEZONE('UTC', #{name})"
+    else
+      name
+    end
+  end
+
+  def column_type(name)
+    membership.columns_hash[name].sql_type
+  end
 end

spec/migrations/orphaned_invite_tokens_cleanup_spec.rb

@@ -16,7 +16,7 @@ RSpec.describe OrphanedInviteTokensCleanup, :migration do
     table(:members).create!(defaults.merge(extra_attributes))
   end
 
-  describe '#up', :aggregate_failures do
+  shared_examples 'removes orphaned invite tokens' do
     it 'removes invite tokens for accepted records with invite_accepted_at < created_at' do
       record1 = create_member(invite_token: 'foo', invite_accepted_at: 1.day.ago, created_at: 1.hour.ago)
       record2 = create_member(invite_token: 'foo2', invite_accepted_at: nil, created_at: 1.hour.ago)
@@ -29,4 +29,22 @@ RSpec.describe OrphanedInviteTokensCleanup, :migration do
       expect(table(:members).find(record3.id).invite_token).to eq 'foo3'
     end
   end
+
+  describe '#up', :aggregate_failures do
+    it_behaves_like 'removes orphaned invite tokens'
+  end
+
+  context 'when there is a mix of timestamptz and timestamp types' do
+    around do |example|
+      ActiveRecord::Base.connection.execute "ALTER TABLE members alter created_at type timestamp with time zone"
+
+      example.run
+
+      ActiveRecord::Base.connection.execute "ALTER TABLE members alter created_at type timestamp without time zone"
+    end
+
+    describe '#up', :aggregate_failures do
+      it_behaves_like 'removes orphaned invite tokens'
+    end
+  end
 end