chore: import upstream snapshot with attribution

server/ast/drop_function.go

@@ -0,0 +1,70 @@
+// 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 ast
+
+import (
+	"fmt"
+
+	vitess "github.com/dolthub/vitess/go/vt/sqlparser"
+
+	"github.com/dolthub/doltgresql/postgres/parser/sem/tree"
+	pgnodes "github.com/dolthub/doltgresql/server/node"
+)
+
+// nodeDropFunction handles *tree.DropFunction nodes.
+func nodeDropFunction(ctx *Context, node *tree.DropFunction) (vitess.Statement, error) {
+	if node == nil {
+		return nil, nil
+	}
+
+	if node.DropBehavior == tree.DropCascade {
+		return nil, fmt.Errorf("DROP FUNCTION with CASCADE is not supported yet")
+	}
+
+	if len(node.Functions) == 0 {
+		return nil, fmt.Errorf("no function name specified for DROP FUNCTION")
+	}
+
+	functions := make([]*pgnodes.RoutineWithParams, len(node.Functions))
+	for i, fn := range node.Functions {
+		var args []pgnodes.RoutineParam
+		for _, a := range fn.Args {
+			if a.Mode != tree.RoutineArgModeOut {
+				_, dt, err := nodeResolvableTypeReference(ctx, a.Type, false)
+				if err != nil {
+					return nil, err
+				}
+				args = append(args, pgnodes.RoutineParam{
+					Name: a.Name.String(),
+					Type: dt,
+				})
+			}
+		}
+		objName := fn.Name.ToTableName()
+		functions[i] = &pgnodes.RoutineWithParams{
+			Args:        args,
+			SchemaName:  objName.Schema(),
+			RoutineName: objName.Object(),
+		}
+	}
+
+	return vitess.InjectedStatement{
+		Statement: pgnodes.NewDropFunction(
+			node.IfExists,
+			functions,
+			node.DropBehavior == tree.DropCascade),
+		Children: nil,
+	}, nil
+}