Convert column DEFAULTs in CREATE TABLE statements (#553)

Convert inline `DEFAULT` values in `CREATE TABLE` statements like this:

```sql
CREATE TABLE foo(a text DEFAULT 'foo')
```

into `OpCreateTable` operations like this:

```json
[
  {
    "create_table": {
      "columns": [
        {
          "default": "'foo'",
          "name": "a",
          "nullable": true,
          "type": "text"
        }
      ],
      "name": "foo"
    }
  }
]
```

Author: andrew-farries

pkg/sql2pgroll/create_table.go

@@ -98,6 +98,7 @@ func convertColumnDef(tableName string, col *pgq.ColumnDef) (*migrations.Column,
 	// Convert column constraints
 	var notNull, pk, unique bool
 	var check *migrations.CheckConstraint
+	var defaultValue *string
 	for _, c := range col.GetConstraints() {
 		switch c.GetConstraint().GetContype() {
 		case pgq.ConstrType_CONSTR_NULL:
@@ -123,6 +124,12 @@ func convertColumnDef(tableName string, col *pgq.ColumnDef) (*migrations.Column,
 			if check == nil {
 				return nil, nil
 			}
+		case pgq.ConstrType_CONSTR_DEFAULT:
+			d, err := pgq.DeparseExpr(c.GetConstraint().GetRawExpr())
+			if err != nil {
+				return nil, fmt.Errorf("error deparsing default value: %w", err)
+			}
+			defaultValue = &d
 		case pgq.ConstrType_CONSTR_FOREIGN:
 			if !canConvertForeignKeyConstraint(c.GetConstraint()) {
 				return nil, nil
@@ -136,6 +143,7 @@ func convertColumnDef(tableName string, col *pgq.ColumnDef) (*migrations.Column,
 		Nullable: !notNull,
 		Pk:       pk,
 		Check:    check,
+		Default:  defaultValue,
 		Unique:   unique,
 	}, nil
 }

pkg/sql2pgroll/create_table_test.go

@@ -44,6 +44,10 @@ func TestConvertCreateTableStatements(t *testing.T) {
 			sql:        "CREATE TABLE foo(a int CHECK (a > 0))",
 			expectedOp: expect.CreateTableOp10,
 		},
+		{
+			sql:        "CREATE TABLE foo(a timestamptz DEFAULT now())",
+			expectedOp: expect.CreateTableOp11,
+		},
 		{
 			sql:        "CREATE TABLE foo(a varchar(255))",
 			expectedOp: expect.CreateTableOp3,

pkg/sql2pgroll/expect/create_table.go

@@ -117,3 +117,15 @@ var CreateTableOp10 = &migrations.OpCreateTable{
 		},
 	},
 }
+
+var CreateTableOp11 = &migrations.OpCreateTable{
+	Name: "foo",
+	Columns: []migrations.Column{
+		{
+			Name:     "a",
+			Type:     "timestamptz",
+			Nullable: true,
+			Default:  ptr("now()"),
+		},
+	},
+}