// Copyright 2026 The Go Language Server Authors

// SPDX-License-Identifier: BSD-3-Clause

package protocol

import (

"github.com/go-json-experiment/json"

"github.com/go-json-experiment/json/jsontext"

)

// Optional wraps a non-nullable optional LSP property, preserving whether a

// zero value such as "" or false was present on the wire. A JSON null clears the

// value to match the legacy pointer representation, where null and absent both

// decoded to nil and were omitted on marshal.

type Optional[T any] struct {

value T

set bool

}

// NewOptional returns an Optional holding v.

func NewOptional[T any](v T) Optional[T] { return Optional[T]{set: true, value: v} }

// IsZero reports whether the value is absent. It drives the ",omitzero" tag so

// an unset Optional is omitted entirely.

func (o Optional[T]) IsZero() bool { return !o.set }

// Get returns the wrapped value and whether it is present.

func (o Optional[T]) Get() (T, bool) { return o.value, o.set }

// Set marks the Optional present with v.

func (o *Optional[T]) Set(v T) {

o.set = true

o.value = v

}

// Clear marks the Optional absent and clears the stored value.

func (o *Optional[T]) Clear() {

var zero T

o.set = false

o.value = zero

}

// MarshalJSONTo implements json.MarshalerTo, streaming the wrapped value (or

// null when absent) through enc so encoder options propagate without

// materializing intermediate bytes per field.

func (o Optional[T]) MarshalJSONTo(enc *jsontext.Encoder) error {

if !o.set {

return enc.WriteToken(jsontext.Null)

}

return json.MarshalEncode(enc, &o.value)

}

// UnmarshalJSONFrom implements json.UnmarshalerFrom. It decodes the value in

// place on the caller's decoder — re-applying the union unmarshalers so nested

// union values dispatch even when the decoder was not built by [Unmarshal] —

// instead of materializing the value bytes and re-parsing them with a fresh

// decoder per field.

func (o *Optional[T]) UnmarshalJSONFrom(dec *jsontext.Decoder) error {

if dec.PeekKind() == 'n' {

if _, err := dec.ReadToken(); err != nil {

return err

}

o.Clear()

return nil

}

o.set = true

return json.UnmarshalDecode(dec, &o.value, json.WithUnmarshalers(unionUnmarshalers))

}