chore: import upstream snapshot with attribution

server/node/show_schemas.go

@@ -0,0 +1,125 @@
+// 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 node
+
+import (
+	"context"
+
+	"github.com/cockroachdb/errors"
+	"github.com/dolthub/go-mysql-server/sql"
+
+	"github.com/dolthub/doltgresql/core"
+	"github.com/dolthub/doltgresql/server/types"
+)
+
+// ShowSchemas is a node that implements the SHOW SCHEMAS	statement.
+type ShowSchemas struct {
+	// TODO: we need planbuilder integration to support SHOW SCHEMAS, rather than getting everything at runtime
+	database string
+}
+
+var _ sql.ExecSourceRel = (*ShowSchemas)(nil)
+
+// NewShowSchemas returns a new *ShowSchemas.
+func NewShowSchemas(database string) *ShowSchemas {
+	return &ShowSchemas{
+		database: database,
+	}
+}
+
+// Children implements the interface sql.ExecSourceRel.
+func (s *ShowSchemas) Children() []sql.Node {
+	return []sql.Node{}
+}
+
+// IsReadOnly implements the interface sql.ExecSourceRel.
+func (s *ShowSchemas) IsReadOnly() bool {
+	return true
+}
+
+// Resolved implements the interface sql.ExecSourceRel.
+func (s *ShowSchemas) Resolved() bool {
+	return true
+}
+
+// RowIter implements the interface sql.ExecSourceRel.
+func (s *ShowSchemas) RowIter(ctx *sql.Context, r sql.Row) (sql.RowIter, error) {
+	database := s.database
+	if database == "" {
+		database = ctx.GetCurrentDatabase()
+		if database == "" {
+			return nil, errors.New("no database selected (this is a bug)")
+		}
+	}
+
+	db, err := core.GetSqlDatabaseFromContext(ctx, database)
+	if err != nil {
+		return nil, err
+	}
+
+	if db == nil {
+		return nil, errors.New("database not found: " + database)
+	}
+
+	sdb, ok := db.(sql.SchemaDatabase)
+	if !ok {
+		// This handles any database that doesn't support schemas (such as some system databases)
+		// TODO: mirror the postgres behavior of returning, every database should have schemas
+		return sql.RowsToRowIter(), nil
+	}
+
+	schemas, err := sdb.AllSchemas(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	rows := make([]sql.Row, len(schemas))
+	for i, schema := range schemas {
+		rows[i] = sql.Row{schema.SchemaName()}
+	}
+
+	return sql.RowsToRowIter(rows...), nil
+}
+
+// Schema implements the interface sql.ExecSourceRel.
+func (s *ShowSchemas) Schema(ctx *sql.Context) sql.Schema {
+	return sql.Schema{
+		{Name: "schema_name", Type: types.Text, Source: "show schemas"},
+	}
+}
+
+// String implements the interface sql.ExecSourceRel.
+func (s *ShowSchemas) String() string {
+	if s.database == "" {
+		return "SHOW SCHEMAS FROM " + s.database
+	}
+	return "SHOW SCHEMAS"
+}
+
+// WithChildren implements the interface sql.ExecSourceRel.
+func (s *ShowSchemas) WithChildren(ctx *sql.Context, children ...sql.Node) (sql.Node, error) {
+	if len(children) != 0 {
+		return nil, errors.New("SHOW SCHEMAS does not support children")
+	}
+	return s, nil
+}
+
+// WithResolvedChildren implements the interface vitess.InjectedStatement.
+func (s *ShowSchemas) WithResolvedChildren(ctx context.Context, children []any) (any, error) {
+	if len(children) != 0 {
+		return nil, errors.New("SHOW SCHEMAS does not support children")
+	}
+	return s, nil
+}