chore: import upstream snapshot with attribution

server/expression/array_flatten.go

@@ -0,0 +1,113 @@
+// Copyright 2025 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package expression
+
+import (
+	"context"
+
+	"github.com/cockroachdb/errors"
+	"github.com/dolthub/go-mysql-server/sql"
+	"github.com/dolthub/go-mysql-server/sql/plan"
+	gmstypes "github.com/dolthub/go-mysql-server/sql/types"
+	vitess "github.com/dolthub/vitess/go/vt/sqlparser"
+
+	"github.com/dolthub/doltgresql/server/types"
+)
+
+// ArrayFlatten is an expression that represents the results of a subquery expression as an array.
+// Currently only subqueries that return a single column are supported.
+type ArrayFlatten struct {
+	Subquery sql.Expression
+}
+
+var _ vitess.Injectable = (*ArrayFlatten)(nil)
+var _ sql.Expression = (*ArrayFlatten)(nil)
+
+// Resolved implements sql.Expression.
+func (a ArrayFlatten) Resolved() bool {
+	return a.Subquery.Resolved()
+}
+
+// String implements sql.Expression.
+func (a ArrayFlatten) String() string {
+	return "ARRAY(" + a.Subquery.String() + ")"
+}
+
+// Type implements sql.Expression.
+func (a ArrayFlatten) Type(ctx *sql.Context) sql.Type {
+	sqType := a.Subquery.Type(ctx)
+	dt, ok := sqType.(*types.DoltgresType)
+	if !ok {
+		// If we don't have a doltgres type, we'll error out at execution time. A special case is the tuple type,
+		// where we need to choose a single one to avoid erroring out too early.
+		if tt, ok := sqType.(gmstypes.TupleType); ok {
+			return tt[0]
+		}
+		return sqType
+	}
+	return dt.ToArrayType()
+}
+
+// IsNullable implements sql.Expression.
+func (a ArrayFlatten) IsNullable(ctx *sql.Context) bool {
+	return false
+}
+
+// Eval implements sql.Expression.
+func (a ArrayFlatten) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
+	subquery, ok := a.Subquery.(*plan.Subquery)
+	if !ok {
+		return nil, errors.Errorf("expected subquery, got %T", a.Subquery)
+	}
+
+	sqType := subquery.Type(ctx)
+	_, ok = sqType.(*types.DoltgresType)
+	if !ok {
+		if tt, ok := sqType.(gmstypes.TupleType); ok {
+			return nil, errors.Errorf("only a single column subquery is supported in ARRAY(), got %d columns", len(tt))
+		}
+		return nil, errors.Errorf("expected doltgres type, got %T", sqType)
+	}
+
+	return subquery.EvalMultiple(ctx, row)
+}
+
+// Children implements sql.Expression.
+func (a ArrayFlatten) Children() []sql.Expression {
+	return []sql.Expression{a.Subquery}
+}
+
+// WithChildren implements sql.Expression.
+func (a ArrayFlatten) WithChildren(ctx *sql.Context, children ...sql.Expression) (sql.Expression, error) {
+	if len(children) != 1 {
+		return nil, sql.ErrInvalidChildrenNumber.New(a, len(children), 1)
+	}
+
+	return ArrayFlatten{Subquery: children[0]}, nil
+}
+
+// WithResolvedChildren implements vitess.Injectable.
+func (a ArrayFlatten) WithResolvedChildren(ctx context.Context, children []any) (any, error) {
+	if len(children) != 1 {
+		return nil, sql.ErrInvalidChildrenNumber.New(a, len(children), 1)
+	}
+
+	subquery, ok := children[0].(sql.Expression)
+	if !ok {
+		return nil, sql.ErrInvalidChildType.New(a, 0, children[0])
+	}
+
+	return ArrayFlatten{Subquery: subquery}, nil
+}