wit/bindgen,cm: marshal & unmarshal for record types

cm/list.go

@@ -1,6 +1,9 @@
 package cm
 
-import "unsafe"
+import (
+	"encoding/json"
+	"unsafe"
+)
 
 // List represents a Component Model list.
 // The binary representation of list<T> is similar to a Go slice minus the cap field.
@@ -9,6 +12,20 @@ type List[T any] struct {
 	list[T]
 }
 
+func (l List[T]) MarshalJSON() ([]byte, error) {
+	return json.Marshal(l.Slice())
+}
+
+func (l *List[T]) UnmarshalJSON(buf []byte) error {
+	var data []T
+	err := json.Unmarshal(buf, &data)
+	if err != nil {
+		return err
+	}
+	*l = ToList(data)
+	return nil
+}
+
 // AnyList is a type constraint for generic functions that accept any [List] type.
 type AnyList[T any] interface {
 	~struct {

cm/option.go

@@ -1,5 +1,9 @@
 package cm
 
+import (
+	"encoding/json"
+)
+
 // Option represents a Component Model [option<T>] type.
 //
 // [option<T>]: https://component-model.bytecodealliance.org/design/wit.html#options
@@ -8,6 +12,27 @@ type Option[T any] struct {
 	option[T]
 }
 
+// MarshalJSON implements the json.Marshaler interface for [Option].
+func (o Option[T]) MarshalJSON() ([]byte, error) {
+	return json.Marshal(o.Some())
+}
+
+// UnmarshalJSON unmarshals the Option from JSON.
+func (o *Option[T]) UnmarshalJSON(buf []byte) error {
+	if len(buf) == 0 {
+		*o = None[T]()
+		return nil
+	}
+
+	var v T
+	if err := json.Unmarshal(buf, &v); err != nil {
+		return err
+	}
+
+	*o = Some(v)
+	return nil
+}
+
 // None returns an [Option] representing the none case,
 // equivalent to the zero value.
 func None[T any]() Option[T] {