Consider using golangci-lint

[lestrrat]

I just realized that the project does not run any code linters, when I noticed that some variables in encode_string.go were not used. Some of these are frivolous, but the amount of unused code kind of worries me.

Can we add a Github action to run golangci-lint? I can create a PR.

Meanwhile, here's the current status

% golangci-lint run ./...
decode_string.go:153:6: `appendCoerceInvalidUTF8` is unused (deadcode)
func appendCoerceInvalidUTF8(b []byte, s []byte) []byte {
     ^
encode.go:44:2: `opCodeEscapedType` is unused (deadcode)
	opCodeEscapedType = iota
	^
encode.go:45:2: `opCodeEscapedIndentType` is unused (deadcode)
	opCodeEscapedIndentType
	^
encode.go:46:2: `opCodeNoEscapeType` is unused (deadcode)
	opCodeNoEscapeType
	^
encode.go:47:2: `opCodeNoEscapeIndentType` is unused (deadcode)
	opCodeNoEscapeIndentType
	^
encode.go:73:2: `codePool` is unused (deadcode)
	codePool         sync.Pool
	^
encode.go:372:6: `encodeBytes` is unused (deadcode)
func encodeBytes(dst []byte, src []byte) []byte {
     ^
encode_string.go:357:5: `htmlSafeSet` is unused (deadcode)
var htmlSafeSet = [256]bool{
    ^
encode_string.go:590:5: `safeSet` is unused (deadcode)
var safeSet = [utf8.RuneSelf]bool{
    ^
encode_string.go:722:6: `escapeIndexWithHTMLEscape` is unused (deadcode)
func escapeIndexWithHTMLEscape(s string) int {
     ^
decode_test.go:2085:5: `interfaceSetTests` is unused (deadcode)
var interfaceSetTests = []struct {
    ^
decode_test.go:2314:5: `decodeTypeErrorTests` is unused (deadcode)
var decodeTypeErrorTests = []struct {
    ^
decode_test.go:2479:5: `invalidUnmarshalTests` is unused (deadcode)
var invalidUnmarshalTests = []struct {
    ^
decode_test.go:2504:5: `invalidUnmarshalTextTests` is unused (deadcode)
var invalidUnmarshalTextTests = []struct {
    ^
stream_test.go:325:5: `tokenStreamCases` is unused (deadcode)
var tokenStreamCases = []tokenStreamCase{
    ^
cover_helper_test.go:29:12: Error return value of `enc.Encode` is not checked (errcheck)
	enc.Encode(data)
	          ^
decode_test.go:2736:16: Error return value of `json.Unmarshal` is not checked (errcheck)
	json.Unmarshal([]byte("{}"), &unmarshalPanic{})
	              ^
encode_test.go:830:14: Error return value of `json.Marshal` is not checked (errcheck)
	json.Marshal(&marshalPanic{})
	            ^
example_test.go:262:13: Error return value of `json.Indent` is not checked (errcheck)
	json.Indent(&out, b, "=", "\t")
	           ^
example_test.go:263:13: Error return value of `out.WriteTo` is not checked (errcheck)
	out.WriteTo(os.Stdout)
	           ^
example_test.go:310:13: Error return value of `out.WriteTo` is not checked (errcheck)
	out.WriteTo(os.Stdout)
	           ^
stream_test.go:88:13: Error return value of `enc.Encode` is not checked (errcheck)
		enc.Encode(v)
		          ^
stream_test.go:303:13: Error return value of `w.Write` is not checked (errcheck)
		go w.Write([]byte(enc))
		          ^
stream_test.go:438:10: Error return value of `w.Write` is not checked (errcheck)
		w.Write([]byte(raw))
		       ^
decode_map.go:154:3: ineffectual assignment to `cursor` (ineffassign)
		cursor = valueCursor
		^
decode_stream.go:19:2: `readPos` is unused (structcheck)
	readPos               int64
	^
decode.go:25:2: `disallowUnknownFields` is unused (structcheck)
	disallowUnknownFields bool
	^
encode_context.go:31:2: `iter` is unused (structcheck)
	iter  unsafe.Pointer
	^
decode_test.go:423:2: `x` is unused (structcheck)
	x int
	^
decode_test.go:1366:2: `unexported` is unused (structcheck)
	unexported int
	^
decode_test.go:2363:2: `m` is unused (structcheck)
	m    map[string]interface{} `json:"-"`
	^
decode_test.go:2364:2: `m2` is unused (structcheck)
	m2   map[string]interface{} `json:"abcd"`
	^
decode_test.go:2366:2: `s` is unused (structcheck)
	s []int `json:"-"`
	^
stream_test.go:317:2: `json` is unused (structcheck)
	json      string
	^
stream_test.go:318:2: `expTokens` is unused (structcheck)
	expTokens []interface{}
	^
decode_test.go:221:4: S1021: should merge variable declaration with assignment on next line (gosimple)
			var v interface{}
			^
struct_field.go:25:2: S1008: should use 'return tag == "-"' instead of 'if tag == "-" { return true }; return false' (gosimple)
	if tag == "-" {
	^
encode_test.go:107:4: structtag: struct field a has json tag but is not exported (govet)
			a int    `json:"aa"` // private field
			^
encode_test.go:440:4: structtag: struct field a has json tag but is not exported (govet)
			a int    `json:"aa"` // private field
			^
tagkey_test.go:62:2: structtag: struct field tag `:"BadFormat"` not compatible with reflect.StructTag.Get: bad syntax for struct tag key (govet)
	Y string `:"BadFormat"`
	^
decode.go:248:2: unreachable: unreachable code (govet)
	return nil, io.EOF
	^
decode_bytes.go:150:4: unreachable: unreachable code (govet)
			return nil, 0, errUnexpectedEndOfJSON("[]byte", cursor)
			^
decode_context.go:145:2: unreachable: unreachable code (govet)
	return cursor, errUnexpectedEndOfJSON("value of object", cursor)
	^
encode_string.go:771:37: unsafeptr: possible misuse of reflect.SliceHeader (govet)
	return *(*[]uint64)(unsafe.Pointer(&reflect.SliceHeader{
	                                   ^
encode_compile.go:648:4: SA4004: the surrounding loop is unconditionally terminated (staticcheck)
			break
			^
encode_compile.go:772:4: SA4004: the surrounding loop is unconditionally terminated (staticcheck)
			break
			^
encode.go:136:2: SA9003: empty branch (staticcheck)
	if err := setupOpcodeSets(); err != nil {
	^
cover_float32_test.go:1207:7: SA5008: the JSON string option only applies to fields of type string, floating point, integer or bool, or pointers to those (staticcheck)
				} `json:",string"`
				  ^
cover_float32_test.go:1781:7: SA5008: the JSON string option only applies to fields of type string, floating point, integer or bool, or pointers to those (staticcheck)
				} `json:",string"`
				  ^
cover_float32_test.go:1784:7: SA5008: the JSON string option only applies to fields of type string, floating point, integer or bool, or pointers to those (staticcheck)
				} `json:",string"`
				  ^
decode_test.go:1317:14: SA5008: unknown JSON option "dummyopt" (staticcheck)
	Foo2 string `json:"bar2,dummyopt"`
	            ^
encode_test.go:1585:15: SA5008: unknown JSON option "random" (staticcheck)
	Slr []string `json:"slr,random"`
	             ^
stream_test.go:113:15: SA5008: invalid JSON field name "\\" (staticcheck)
		Invalid int `json:"\\"`
		            ^
tagkey_test.go:66:11: SA5008: invalid JSON field name " !\"#&'()*+" (staticcheck)
	Z string `json:" !\"#&'()*+,."`
	         ^
encode_opcode.go:250:18: func `(*opcode).dumpKey` is unused (unused)
decode_test.go:1931:6: type `Xint` is unused (unused)
decode_test.go:589:6: type `XYZ` is unused (unused)
encode_opcode.go:263:18: func `(*opcode).dumpValue` is unused (unused)
decode_test.go:595:6: type `unexportedWithMethods` is unused (unused)
encode_opcode.go:217:18: func `(*opcode).dumpElem` is unused (unused)
encode_opcode.go:205:18: func `(*opcode).dumpMapEnd` is unused (unused)
decode_test.go:645:6: type `byteWithPtrMarshalText` is unused (unused)
encode_opcode.go:237:18: func `(*opcode).dumpField` is unused (unused)
encode_opcode.go:191:18: func `(*opcode).dumpMapHead` is unused (unused)
encode_vm.go:9388:19: func `(*Encoder).ptrToByte` is unused (unused)
encode_opcode.go:274:18: func `(*opcode).dump` is unused (unused)
decode_test.go:1618:6: type `NullTest` is unused (unused)
encode_opcode.go:172:18: func `(*opcode).dumpHead` is unused (unused)

[goccy]

Can we add a Github action to run golangci-lint? I can create a PR.

Yes ! Thank you !! 🙇