entrypoint.sh: Migrate data stores before any other migrations

The migration code checks that the migration hasn't already happened (e.g. by
testing whether prosody.sqlite exists). However we do various other operations
before this point (via prosodyctl) which may initialize the new data store of
the desired type.

If this happens, the migration code will assume that a migration already
happened and skip the migration.

This changes the order to ensure data store migrations always happen first,
and adds a comment to inform future devs about this potential issue.

docker/entrypoint.sh

@@ -50,17 +50,9 @@ if test -f /snikket/prosody/turn-auth-secret; then
 	rm /snikket/prosody/turn-auth-secret;
 fi
 
-if test -d /snikket/prosody/http_upload; then
-	prosodyctl mod_migrate_http_upload "share.$SNIKKET_DOMAIN" "$SNIKKET_DOMAIN"
-fi
-
-# COMPAT: migrate from 0.12 series role storage
-if ! test -d /snikket/prosody/*/account_roles; then
-	prosodyctl mod_authz_internal migrate "$SNIKKET_DOMAIN"
-fi
-
-# Migrate from prosody:normal to prosody:registered
-prosodyctl mod_migrate_snikket_roles migrate "$SNIKKET_DOMAIN"
+# Migrate between storage backends if needed
+# Note: this happens before we do any other operations that touch Prosody's
+# data store, to ensure consistency.
 
 if test "${SNIKKET_TWEAK_STORAGE:-files}" = "sqlite" && ! test -f /snikket/prosody/prosody.sqlite; then
 	sed -i "s/SNIKKET_DOMAIN/$SNIKKET_DOMAIN/" /etc/prosody/migrator.cfg.lua
@@ -86,4 +78,16 @@ elif test "${SNIKKET_TWEAK_STORAGE:-files}" = "files" && test -f /snikket/prosod
 	fi
 fi
 
+if test -d /snikket/prosody/http_upload; then
+	prosodyctl mod_migrate_http_upload "share.$SNIKKET_DOMAIN" "$SNIKKET_DOMAIN"
+fi
+
+# COMPAT: migrate from 0.12 series role storage
+if ! test -d /snikket/prosody/*/account_roles; then
+	prosodyctl mod_authz_internal migrate "$SNIKKET_DOMAIN"
+fi
+
+# Migrate from prosody:normal to prosody:registered
+prosodyctl mod_migrate_snikket_roles migrate "$SNIKKET_DOMAIN"
+
 exec s6-svscan /etc/sv