You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: message.go
    path of file: ./repos/protoreflect/desc/protoparse/ast
    
    the code of the file until where you have to start completion: package ast

import "fmt"

// MessageDeclNode is a node in the AST that defines a message type. This
// includes normal message fields as well as implicit messages:
//   - *MessageNode
//   - *GroupNode (the group is a field and inline message type)
//   - *MapFieldNode (map fields implicitly define a MapEntry message type)
//
// This also allows NoSourceNode to be used
    
func populateMessageBody(m *MessageBody, openBrace *RuneNode, decls []MessageElement, closeBrace *RuneNode) {
	m.OpenBrace = openBrace
	m.Decls = decls
	for _, decl := range decls {
		switch decl.(type) {
		case *OptionNode, *FieldNode, *MapFieldNode, *GroupNode, *OneOfNode,
			*MessageNode, *EnumNode, *ExtendNode, *ExtensionRangeNode,
			*ReservedNode, *EmptyDeclNode:
		default:
			panic(fmt.Sprintf("invalid MessageElement type: %T", decl))
		}
	}
	m.CloseBrace = closeBrace
}