Convert DROP TABLE SQL to pgroll operation (#529)

Converts `DROP TABLE` statements in these forms:

```sql
DROP TABLE foo
DROP TABLE foo RESTRICT
DROP TABLE foo.bar
DROP TABLE IF EXISTS foo
```

These forms fall back to raw SQL:

```sql
DROP TABLE foo CASCADE
```

Part of #504

Author: ryanslade

pkg/sql2pgroll/drop.go

@@ -12,8 +12,12 @@ import (
 
 // convertDropStatement converts supported drop statements to pgroll operations
 func convertDropStatement(stmt *pgq.DropStmt) (migrations.Operations, error) {
-	if stmt.RemoveType == pgq.ObjectType_OBJECT_INDEX {
+	switch stmt.RemoveType {
+	case pgq.ObjectType_OBJECT_INDEX:
 		return convertDropIndexStatement(stmt)
+	case pgq.ObjectType_OBJECT_TABLE:
+		return convertDropTableStatement(stmt)
+
 	}
 	return nil, nil
 }
@@ -46,3 +50,27 @@ func canConvertDropIndex(stmt *pgq.DropStmt) bool {
 	}
 	return true
 }
+
+// convertDropTableStatement converts simple DROP TABLE statements to pgroll operations
+func convertDropTableStatement(stmt *pgq.DropStmt) (migrations.Operations, error) {
+	if !canConvertDropTable(stmt) {
+		return nil, nil
+	}
+
+	items := stmt.GetObjects()[0].GetList().GetItems()
+	parts := make([]string, len(items))
+	for i, item := range items {
+		parts[i] = item.GetString_().GetSval()
+	}
+
+	return migrations.Operations{
+		&migrations.OpDropTable{
+			Name: strings.Join(parts, "."),
+		},
+	}, nil
+}
+
+// canConvertDropTable checks whether we can convert the statement without losing any information.
+func canConvertDropTable(stmt *pgq.DropStmt) bool {
+	return stmt.Behavior != pgq.DropBehavior_DROP_CASCADE
+}

pkg/sql2pgroll/drop_test.go

@@ -54,11 +54,52 @@ func TestDropIndexStatements(t *testing.T) {
 	}
 }
 
-func TestUnconvertableDropIndexStatements(t *testing.T) {
+func TestDropTableStatements(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		sql        string
+		expectedOp migrations.Operation
+	}{
+		{
+			sql:        "DROP TABLE foo",
+			expectedOp: expect.DropTableOp1,
+		},
+		{
+			sql:        "DROP TABLE foo RESTRICT",
+			expectedOp: expect.DropTableOp1,
+		},
+		{
+			sql:        "DROP TABLE IF EXISTS foo",
+			expectedOp: expect.DropTableOp1,
+		},
+		{
+			sql:        "DROP TABLE foo.bar",
+			expectedOp: expect.DropTableOp2,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.sql, func(t *testing.T) {
+			ops, err := sql2pgroll.Convert(tc.sql)
+			require.NoError(t, err)
+
+			require.Len(t, ops, 1)
+
+			assert.Equal(t, tc.expectedOp, ops[0])
+		})
+	}
+}
+
+func TestUnconvertableDropStatements(t *testing.T) {
 	t.Parallel()
 
 	tests := []string{
+		// Drop index
 		"DROP INDEX foo CASCADE",
+
+		// Drop table
+		"DROP TABLE foo CASCADE",
 	}
 
 	for _, sql := range tests {

pkg/sql2pgroll/expect/drop_table.go

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package expect
+
+import (
+	"github.com/xataio/pgroll/pkg/migrations"
+)
+
+var DropTableOp1 = &migrations.OpDropTable{
+	Name: "foo",
+}
+
+var DropTableOp2 = &migrations.OpDropTable{
+	Name: "foo.bar",
+}