refactor(features): hold jsObject's index order and truthiness in tests

Array-index properties are ordered by comparing their canonical
decimal forms instead of parsing them again, and isArrayIndex reports
only whether a key is one. The tests now hold the 2^32-1 bound with
4294967294 and 4294967296, and the truthiness of a number in the
deprecated-property move.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: aledbf

internal/features/jsobject.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"slices"
 	"strconv"
+	"strings"
 	"unicode/utf16"
 )
 
@@ -56,29 +57,27 @@ func (o *jsObject) spread(src *jsObject) *jsObject {
 	return out
 }
 
-// arrayIndex reports whether k is an array index, which JS orders first.
-func arrayIndex(k string) (uint64, bool) {
+// isArrayIndex reports whether k is an array index (a canonical integer
+// below 2^32-1), which JS orders first.
+func isArrayIndex(k string) bool {
 	n, err := strconv.ParseUint(k, 10, 32)
-	if err != nil || n == 1<<32-1 || strconv.FormatUint(n, 10) != k {
-		return 0, false
-	}
-	return n, true
+	return err == nil && n != 1<<32-1 && strconv.FormatUint(n, 10) == k
 }
 
 // order is the order JSON.stringify writes o's properties in.
 func (o *jsObject) order() []string {
 	var idx, rest []string
 	for _, k := range o.keys {
-		if _, ok := arrayIndex(k); ok {
+		if isArrayIndex(k) {
 			idx = append(idx, k)
 		} else {
 			rest = append(rest, k)
 		}
 	}
+	// Array indexes are canonical: shorter is smaller, equal lengths compare
+	// as strings.
 	slices.SortFunc(idx, func(a, b string) int {
-		x, _ := arrayIndex(a)
-		y, _ := arrayIndex(b)
-		return cmp.Compare(x, y)
+		return cmp.Or(cmp.Compare(len(a), len(b)), strings.Compare(a, b))
 	})
 	return append(idx, rest...)
 }

internal/features/jsobject_test.go

@@ -7,15 +7,15 @@ import (
 
 // JSON.parse then JSON.stringify: a repeated property keeps its first
 // position and its last value, array-index properties come first, ascending
-// (4294967295, "01" and "-1" are not indexes), the rest in insertion order.
+// (4294967295 and above, "01" and "-1" are not indexes), the rest in insertion order.
 func TestJSObjectRoundTripsAsJavaScript(t *testing.T) {
-	src := `{"b":1,"4294967295":2,"10":3,"01":4,"2":5,"b":6,"-1":7,"a":[{"z":1,"y":[]}],"n":1.50,"e":1e21}`
+	src := `{"b":1,"4294967295":2,"10":3,"01":4,"2":5,"b":6,"-1":7,"4294967296":8,"9":9,"4294967294":10,"a":[{"z":1,"y":[]}],"n":1.50,"e":1e21}`
 	v, err := parseJS([]byte(src))
 	if err != nil {
 		t.Fatal(err)
 	}
 	got, err := json.Marshal(v)
-	want := `{"2":5,"10":3,"b":6,"4294967295":2,"01":4,"-1":7,"a":[{"z":1,"y":[]}],"n":1.5,"e":1e+21}`
+	want := `{"2":5,"9":9,"10":3,"4294967294":10,"b":6,"4294967295":2,"01":4,"-1":7,"4294967296":8,"a":[{"z":1,"y":[]}],"n":1.5,"e":1e+21}`
 	if err != nil || string(got) != want {
 		t.Errorf("got  %s, %v\nwant %s", got, err, want)
 	}

internal/features/types_order_test.go

@@ -79,6 +79,8 @@ func TestFeatureMarshalJSONMovesDeprecatedProperties(t *testing.T) {
 			`{"id":"c","customizations":{"vscode":{"extensions":"basex,1"}},"included":true,"value":null}`},
 		{`{"id":"d","extensions":[],"settings":"ab"}`,
 			`{"id":"d","included":true,"value":null,"customizations":{"vscode":{"extensions":[],"settings":{"0":"a","1":"b"}}}}`},
+		{`{"id":"g","extensions":0,"settings":1}`,
+			`{"id":"g","extensions":0,"included":true,"value":null,"customizations":{"vscode":{"settings":{}}}}`},
 		{`{"id":"e","extensions":"","settings":null,"devPort":1}`,
 			`{"id":"e","extensions":"","settings":null,"devPort":1,"included":true,"value":null}`},
 	} {