chore: import upstream snapshot with attribution

server/ast/order_by.go

@@ -0,0 +1,83 @@
+// Copyright 2023 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 ast
+
+import (
+	"github.com/cockroachdb/errors"
+	"github.com/dolthub/go-mysql-server/sql/expression"
+
+	vitess "github.com/dolthub/vitess/go/vt/sqlparser"
+
+	"github.com/dolthub/doltgresql/postgres/parser/sem/tree"
+	pgexprs "github.com/dolthub/doltgresql/server/expression"
+)
+
+// nodeOrderBy handles *tree.OrderBy nodes.
+func nodeOrderBy(ctx *Context, node tree.OrderBy) (vitess.OrderBy, error) {
+	if len(node) == 0 {
+		return nil, nil
+	}
+	orderBys := make([]*vitess.Order, len(node))
+	for i := range node {
+		if node[i].OrderType != tree.OrderByColumn {
+			return nil, errors.Errorf("ORDER BY type is not yet supported")
+		}
+		var direction string
+		switch node[i].Direction {
+		case tree.DefaultDirection:
+			direction = vitess.AscScr
+		case tree.Ascending:
+			direction = vitess.AscScr
+		case tree.Descending:
+			direction = vitess.DescScr
+		default:
+			return nil, errors.Errorf("unknown ORDER BY sorting direction")
+		}
+		switch node[i].NullsOrder {
+		case tree.DefaultNullsOrder:
+			//TODO: the default NULL order is reversed compared to MySQL, so the default is technically always wrong.
+			// To prevent choking on every ORDER BY, we allow this to proceed (even with incorrect results) for now.
+			// If the NULL order is explicitly declared, then we want to error rather than return incorrect results.
+		case tree.NullsFirst:
+			if direction != vitess.AscScr {
+				return nil, errors.Errorf("this NULL ordering is not yet supported for this ORDER BY direction")
+			}
+		case tree.NullsLast:
+			if direction != vitess.DescScr {
+				return nil, errors.Errorf("this NULL ordering is not yet supported for this ORDER BY direction")
+			}
+		default:
+			return nil, errors.Errorf("unknown NULL ordering in ORDER BY")
+		}
+		expr, err := nodeExpr(ctx, node[i].Expr)
+		if err != nil {
+			return nil, err
+		}
+		// GMS order by is hardcoded to expect vitess.SQLVal for expressions such as `ORDER BY 1`.
+		// In addition, there is the requirement that columns in the order by also need to be referenced somewhere in
+		// the query, which is not a requirement for Postgres. Whenever we add that functionality, we also need to
+		// remove the dependency on vitess.SQLVal. For now, we'll just convert our literals to a vitess.SQLVal.
+		if injectedExpr, ok := expr.(vitess.InjectedExpr); ok {
+			if literal, ok := injectedExpr.Expression.(*expression.Literal); ok {
+				expr = pgexprs.ToVitessLiteral(literal)
+			}
+		}
+		orderBys[i] = &vitess.Order{
+			Expr:      expr,
+			Direction: direction,
+		}
+	}
+	return orderBys, nil
+}