fixup: Add comments to MIGRATIONS list

Author: tankyleo

rust/impls/src/postgres_store.rs

@@ -39,12 +39,18 @@ const LOG_MIGRATION_STMT: &str = "INSERT INTO vss_db_upgrades VALUES($1);";
 #[cfg(test)]
 const GET_MIGRATION_LOG_STMT: &str = "SELECT upgrade_from FROM vss_db_upgrades;";
 
+// APPEND-ONLY list of migration statements
+//
+// Each statement MUST be applied in-order, and only once per database.
+//
+// We make an exception for the vss_db table creation statement, as users of VSS could have initialized the table
+// themselves.
 const MIGRATIONS: &[&str] = &[
 	"CREATE TABLE vss_db_version (db_version INTEGER);",
 	"INSERT INTO vss_db_version VALUES(1);",
+	// A write-only log of all the migrations performed on this database, useful for debugging and testing
 	"CREATE TABLE vss_db_upgrades (upgrade_from INTEGER);",
-	// We do not complain if the table already exists, as a previous version of VSS could have already created
-	// this table
+	// We do not complain if the table already exists, as users of VSS could have already created this table
 	"CREATE TABLE IF NOT EXISTS vss_db (
 	    user_token character varying(120) NOT NULL CHECK (user_token <> ''),
 	    store_id character varying(120) NOT NULL CHECK (store_id <> ''),