fix: Copy strings from tokens

internal/unescape/unescape.go

@@ -8,22 +8,24 @@ import (
 // Valid returns the unescaped version of str relying on str to be valid.
 // Don't use this function if str isn't guaranteed to contain no
 // invalid escape sequences.
-func Valid[S ~[]byte | ~string, O ~[]byte | ~string](str S) O {
+func Valid[S []byte | string, O []byte | string](str S) O {
 	var oz O
 	if len(str) < 1 {
 		return oz
 	}
+
+	// Copy the string because it probably originates from a token
+	// which will be reused across Decode calls.
 	var s string
 	switch in := any(str).(type) {
 	case string:
-		s = in
+		cp := unsafe.Slice(unsafe.StringData(in), len(in))
+		copy(cp, in)
+		s = unsafe.String(unsafe.SliceData(cp), len(in))
 	case []byte:
-		// Avoid copying str to a string, treat the bytes as read-only instead
-		// since str is guaranteed to remain immutable.
-		s = unsafe.String(unsafe.SliceData(in), len(in))
-	default:
-		s = string(str)
+		s = string(in)
 	}
+
 	i := strings.IndexByte(s, '\\')
 	if i < 0 {
 		return O(s)

internal/unescape/unescape_test.go

@@ -116,7 +116,7 @@ var tests = []test{
 	}(),
 }
 
-func runTestValid[S ~[]byte | ~string, O ~[]byte | ~string](
+func runTestValid[S []byte | string, O []byte | string](
 	t *testing.T, name string, input S, expect O,
 ) {
 	t.Run(name, func(t *testing.T) {
@@ -138,7 +138,6 @@ func runTestValid[S ~[]byte | ~string, O ~[]byte | ~string](
 }
 
 func TestValid(t *testing.T) {
-	type CustomString string
 	for _, td := range tests {
 		runTestValid[string, string](
 			t, td.Name+"/string2string", td.Input, td.Expect,
@@ -152,9 +151,6 @@ func TestValid(t *testing.T) {
 		runTestValid[[]byte, string](
 			t, td.Name+"/bytes2string", []byte(td.Input), td.Expect,
 		)
-		runTestValid[CustomString, CustomString](
-			t, td.Name+"/bytes2string", CustomString(td.Input), CustomString(td.Expect),
-		)
 	}
 }
 

jscandec.go

@@ -3524,7 +3524,7 @@ func fieldFrameIndexByName[S []byte | string](fields []fieldStackFrame, name S)
 	return noParentFrame
 }
 
-func decodeAny[S ~[]byte | ~string](
+func decodeAny[S []byte | string](
 	str S, tokens []jscan.Token[S],
 ) (any, []jscan.Token[S], error) {
 	switch tokens[0].Type {