Make go module, marshal userdata as json(null), and encode sparse arrays

go.mod

@@ -0,0 +1,5 @@
+module github.com/layeh/gopher-json
+
+go 1.19
+
+require github.com/yuin/gopher-lua v0.0.0-20221210110428-332342483e3f

go.sum

@@ -0,0 +1,2 @@
+github.com/yuin/gopher-lua v0.0.0-20221210110428-332342483e3f h1:wihIB0V/mGpVYrL8I7n/WxVqWnP07CBXZ5uCgxUP1tI=
+github.com/yuin/gopher-lua v0.0.0-20221210110428-332342483e3f/go.mod h1:GBR0iDaNXjAgGg9zfCvksxSRnQx76gclCIb7kdAd1Pw=

json.go

@@ -3,8 +3,9 @@ package json
 import (
 	"encoding/json"
 	"errors"
+	"fmt"
 
-	"github.com/yuin/gopher-lua"
+	lua "github.com/yuin/gopher-lua"
 )
 
 // Preload adds json to the given Lua state's package.preload table. After it
@@ -56,7 +57,6 @@ func apiEncode(L *lua.LState) int {
 
 var (
 	errNested      = errors.New("cannot encode recursively nested tables to JSON")
-	errSparseArray = errors.New("cannot encode sparse array")
 	errInvalidKeys = errors.New("cannot encode mixed or invalid key types")
 )
 
@@ -109,10 +109,11 @@ func (j jsonValue) MarshalJSON() (data []byte, err error) {
 					return
 				}
 				if expectedKey != key {
-					err = errSparseArray
-					return
+					errValue := lua.LString(fmt.Sprintf("[%s] = %s", key.String(), value.String()))
+					arr = append(arr, jsonValue{errValue, j.visited})
+				} else {
+					arr = append(arr, jsonValue{value, j.visited})
 				}
-				arr = append(arr, jsonValue{value, j.visited})
 				expectedKey++
 				key, value = converted.Next(key)
 			}
@@ -131,6 +132,9 @@ func (j jsonValue) MarshalJSON() (data []byte, err error) {
 		default:
 			err = errInvalidKeys
 		}
+	case *lua.LUserData:
+		data, err = json.Marshal(nil)
+		return
 	default:
 		err = invalidTypeError(j.LValue.Type())
 	}

json_test.go

@@ -2,9 +2,10 @@ package json
 
 import (
 	"encoding/json"
+	"fmt"
 	"testing"
 
-	"github.com/yuin/gopher-lua"
+	lua "github.com/yuin/gopher-lua"
 )
 
 func TestSimple(t *testing.T) {
@@ -21,9 +22,6 @@ func TestSimple(t *testing.T) {
 	assert(json.encode({}) == "[]")
 	assert(json.encode({1, 2, 3}) == "[1,2,3]")
 
-	local _, err = json.encode({1, 2, [10] = 3})
-	assert(string.find(err, "sparse array"))
-
 	local _, err = json.encode({1, 2, 3, name = "Tim"})
 	assert(string.find(err, "mixed or invalid key types"))
 
@@ -62,6 +60,8 @@ func TestSimple(t *testing.T) {
 		a[i] = i
 	end
 	assert(json.encode(a) == "[1,2,3,4,5]")
+
+	assert(json.encode(json) == nil)
 	`
 	s := lua.NewState()
 	defer s.Close()
@@ -97,3 +97,59 @@ func TestDecodeValue_jsonNumber(t *testing.T) {
 		t.Fatalf("expecting LString, got %T", v)
 	}
 }
+
+func TestEncode_SparseArray(t *testing.T) {
+	tests := []struct {
+		table    string
+		expected string
+	}{
+		{
+			table: `{
+				1,
+				2,
+				[10] = 3
+			}`,
+			expected: `[1,2,"[10] = 3"]`,
+		},
+		{
+			table: `{
+				nested = {
+					[37] = "index 37"
+				}
+			}`,
+			expected: `{"nested":["[37] = index 37"]}`,
+		},
+		{
+			table: `{
+				nested = {
+					"index 1",
+					[37] = "index 37"
+				}
+			}`,
+			expected: `{"nested":["index 1","[37] = index 37"]}`,
+		},
+		{
+			table: `{
+				nested = {
+					"index 1",
+					[37] = "index 37"
+				}
+			}`,
+			expected: `{"nested":["index 1","[37] = index 37"]}`,
+		},
+	}
+
+	for _, test := range tests {
+		s := lua.NewState()
+		defer s.Close()
+		Preload(s)
+
+		luaScript := fmt.Sprintf(`
+			local json = require("json")
+			local t = %s
+			assert(json.encode(t) == '%s')`, test.table, test.expected)
+		if err := s.DoString(luaScript); err != nil {
+			t.Error(err)
+		}
+	}
+}