Allow adding a column to a table created in the same migration (#449)

Allow the `add_column` operation to add a column to a table that was
created by an operation earlier in the same migration.

The following migration would previously have failed to start:

```json
{
  "name": "43_multiple_ops",
  "operations": [
    {
      "create_table": {
        "name": "players",
        "columns": [
          {
            "name": "id",
            "type": "serial",
            "pk": true
          },
          {
            "name": "name",
            "type": "varchar(255)",
            "check": {
              "name": "name_length_check",
              "constraint": "length(name) > 2"
            }
          }
        ]
      }
    },
    {
      "add_column": {
        "table": "players",
        "column": {
          "name": "rating",
          "type": "integer",
          "comment": "hello world",
          "check": {
            "name": "rating_check",
            "constraint": "rating > 0 AND rating < 100"
          },
          "nullable": false
        }
      }
    }
  ]
}
```

As of this PR, the migration can be started.

The above migration does not validate yet, but it can be started
successfully with the `--skip-validation` flag to the `start` command.

Part of #239

Author: andrew-farries

pkg/migrations/op_add_column.go

@@ -24,19 +24,19 @@ func (o *OpAddColumn) Start(ctx context.Context, conn db.DB, latestSchema string
 	}
 
 	if o.Column.Comment != nil {
-		if err := addCommentToColumn(ctx, conn, o.Table, TemporaryName(o.Column.Name), o.Column.Comment); err != nil {
+		if err := addCommentToColumn(ctx, conn, table.Name, TemporaryName(o.Column.Name), o.Column.Comment); err != nil {
 			return nil, fmt.Errorf("failed to add comment to column: %w", err)
 		}
 	}
 
 	if !o.Column.IsNullable() && o.Column.Default == nil {
-		if err := addNotNullConstraint(ctx, conn, o.Table, o.Column.Name, TemporaryName(o.Column.Name)); err != nil {
+		if err := addNotNullConstraint(ctx, conn, table.Name, o.Column.Name, TemporaryName(o.Column.Name)); err != nil {
 			return nil, fmt.Errorf("failed to add not null constraint: %w", err)
 		}
 	}
 
 	if o.Column.Check != nil {
-		if err := o.addCheckConstraint(ctx, conn); err != nil {
+		if err := o.addCheckConstraint(ctx, table.Name, conn); err != nil {
 			return nil, fmt.Errorf("failed to add check constraint: %w", err)
 		}
 	}
@@ -231,9 +231,9 @@ func addNotNullConstraint(ctx context.Context, conn db.DB, table, column, physic
 	return err
 }
 
-func (o *OpAddColumn) addCheckConstraint(ctx context.Context, conn db.DB) error {
+func (o *OpAddColumn) addCheckConstraint(ctx context.Context, tableName string, conn db.DB) error {
 	_, err := conn.ExecContext(ctx, fmt.Sprintf("ALTER TABLE %s ADD CONSTRAINT %s CHECK (%s) NOT VALID",
-		pq.QuoteIdentifier(o.Table),
+		pq.QuoteIdentifier(tableName),
 		pq.QuoteIdentifier(o.Column.Check.Name),
 		rewriteCheckExpression(o.Column.Check.Constraint, o.Column.Name, TemporaryName(o.Column.Name)),
 	))

pkg/migrations/op_add_column_test.go

@@ -1494,6 +1494,74 @@ func TestAddColumnDefaultTransformation(t *testing.T) {
 	}, roll.WithSQLTransformer(sqlTransformer))
 }
 
+func TestAddColumnToATableCreatedInTheSameMigration(t *testing.T) {
+	t.Parallel()
+
+	ExecuteTests(t, TestCases{
+		{
+			name: "add column to newly created table",
+			migrations: []migrations.Migration{
+				{
+					Name: "01_add_table",
+					Operations: migrations.Operations{
+						&migrations.OpCreateTable{
+							Name: "users",
+							Columns: []migrations.Column{
+								{
+									Name: "id",
+									Type: "serial",
+									Pk:   ptr(true),
+								},
+								{
+									Name: "name",
+									Type: "varchar(255)",
+								},
+							},
+						},
+						&migrations.OpAddColumn{
+							Table: "users",
+							Column: migrations.Column{
+								Name:     "age",
+								Type:     "integer",
+								Nullable: ptr(false),
+								Check: &migrations.CheckConstraint{
+									Name:       "age_check",
+									Constraint: "age >= 18",
+								},
+								Comment: ptr("the age of the user"),
+							},
+						},
+					},
+				},
+			},
+			afterStart: func(t *testing.T, db *sql.DB, schema string) {
+				// Inserting into the new column on the new table works.
+				MustInsert(t, db, schema, "01_add_table", "users", map[string]string{
+					"name": "Alice", "age": "30",
+				})
+
+				// Inserting a value that doesn't meet the check constraint fails.
+				MustNotInsert(t, db, schema, "01_add_table", "users", map[string]string{
+					"name": "Bob", "age": "8",
+				}, testutils.CheckViolationErrorCode)
+			},
+			afterRollback: func(t *testing.T, db *sql.DB, schema string) {
+			},
+			afterComplete: func(t *testing.T, db *sql.DB, schema string) {
+				// Inserting into the new column on the new table works.
+				MustInsert(t, db, schema, "01_add_table", "users", map[string]string{
+					"name": "Bob", "age": "31",
+				})
+
+				// Inserting a value that doesn't meet the check constraint fails.
+				MustNotInsert(t, db, schema, "01_add_table", "users", map[string]string{
+					"name": "Carl", "age": "8",
+				}, testutils.CheckViolationErrorCode)
+			},
+		},
+	}, roll.WithSkipValidation(true)) // TODO: remove once this migration can be validated
+}
+
 func TestAddColumnInvalidNameLength(t *testing.T) {
 	t.Parallel()