Replace implementation of previous_version func

Use a recursive CTE to find the first non-'manual' parent of the current
version.

pkg/state/state.go

@@ -72,7 +72,20 @@ STABLE;
 -- Get the name of the previous version of the schema, or NULL if there is none.
 CREATE OR REPLACE FUNCTION %[1]s.previous_version(schemaname NAME) RETURNS text
 AS $$
-  SELECT parent FROM %[1]s.migrations WHERE name = (SELECT %[1]s.latest_version(schemaname)) AND schema=schemaname;
+  WITH RECURSIVE find_ancestor AS (
+    SELECT schema, name, parent, migration_type FROM pgroll.migrations 
+      WHERE name = (SELECT %[1]s.latest_version(schemaname)) AND schema = schemaname
+
+    UNION ALL
+
+    SELECT m.schema, m.name, m.parent, m.migration_type FROM pgroll.migrations m
+      INNER JOIN find_ancestor fa ON fa.parent = m.name AND fa.schema = m.schema
+      WHERE m.migration_type = 'manual'
+  )
+  SELECT a.parent
+  FROM find_ancestor AS a
+  JOIN pgroll.migrations AS b ON a.parent = b.name AND a.schema = b.schema
+  WHERE b.migration_type = 'pgroll';
 $$
 LANGUAGE SQL
 STABLE;