fix: Postgres Drop() also removes custom enum types

[Yanhu007]

Fixes #626

Problem

Drop() only drops tables but leaves custom types (enums, etc.) behind. When a migration creates a custom type:

CREATE TYPE mytype AS ENUM('a', 'b');

Running Drop() followed by Up() fails:

pq: type "mytype" already exists

Fix

After dropping tables, query pg_type for enum types (typtype = 'e') in the current schema and drop them with CASCADE. This follows the same pattern used for table dropping (iterate + DROP IF EXISTS).

Previous PR #477 was closed without merge. This implementation uses a simpler approach querying pg_type directly.

[Copilot]

Pull request overview

Updates the Postgres driver’s Drop() implementation to fully clean a schema by removing custom enum types in addition to dropping tables, fixing the “type already exists” failure when re-running migrations after Drop().

Changes:

• Query pg_type/pg_namespace for enum types in the current schema (typtype = 'e').
• Iterate found enum types and DROP TYPE IF EXISTS ... CASCADE after tables are dropped.

---

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[Copilot]

types.Err() is wrapped using the mutable query variable, but by the time this runs query may contain the last DROP TYPE ... statement rather than the original SELECT ... FROM pg_type .... This makes the reported query misleading and complicates debugging. Consider keeping the SELECT in a separate variable (e.g., typesQuery) and using that for Query: in errors coming from iteration/scan/Err(), while using a separate dropQuery for the DDL.

[Copilot]

On types.Scan(&typeName) failure, this returns the raw error without attaching the SQL that was executing. Elsewhere in this method, query errors are wrapped with database.Error{..., Query: ...}; doing the same here (using the SELECT query, not the last DROP) would improve error context consistency.

[Copilot]

This new behavior (dropping enum types during Drop()) isn't covered by the existing Postgres driver tests; database/testing.TestDrop only checks that Drop() returns nil. Please add an integration test that creates a custom enum type in the current schema, calls Drop(), and asserts the type no longer exists (or that re-creating the type succeeds) to prevent regressions like #626.

Suggested change

	for types.Next() {
	var typeName string
	if err := types.Scan(&typeName); err != nil {
	return err
	}
	query = `DROP TYPE IF EXISTS ` + pq.QuoteIdentifier(typeName) + ` CASCADE`
	if _, err := p.conn.ExecContext(context.Background(), query); err != nil {
	return &database.Error{OrigErr: err, Query: []byte(query)}
	}
	}
	if err := types.Err(); err != nil {
	return &database.Error{OrigErr: err, Query: []byte(query)}
	}
	typeNames := make([]string, 0)
	for types.Next() {
	var typeName string
	if err := types.Scan(&typeName); err != nil {
	return err
	}
	if len(typeName) > 0 {
	typeNames = append(typeNames, typeName)
	}
	}
	if err := types.Err(); err != nil {
	return &database.Error{OrigErr: err, Query: []byte(query)}
	}
	if len(typeNames) > 0 {
	for _, t := range typeNames {
	query = `DROP TYPE IF EXISTS ` + pq.QuoteIdentifier(t) + ` CASCADE`
	if _, err := p.conn.ExecContext(context.Background(), query); err != nil {
	return &database.Error{OrigErr: err, Query: []byte(query)}
	}
	}
	}

[coveralls]

coverage: 54.377% (-0.06%) from 54.432% — Yanhu007:fix/postgres-drop-all-objects into golang-migrate:master