Fix StrListDelete side effect. (#118)

strutil/strutil.go

@@ -113,11 +113,11 @@ func ParseKeyValues(input string, out map[string]string, sep string) error {
 
 // ParseArbitraryKeyValues parses arbitrary <key,value> tuples. The input
 // can be one of the following:
-// * JSON string
-// * Base64 encoded JSON string
-// * Comma separated list of `<key>=<value>` pairs
-// * Base64 encoded string containing comma separated list of
-//   `<key>=<value>` pairs
+//   - JSON string
+//   - Base64 encoded JSON string
+//   - Comma separated list of `<key>=<value>` pairs
+//   - Base64 encoded string containing comma separated list of
+//     `<key>=<value>` pairs
 //
 // Input will be parsed into the output parameter, which should
 // be a non-nil map[string]string.
@@ -367,7 +367,11 @@ func StrListDelete(s []string, d string) []string {
 
 	for index, element := range s {
 		if element == d {
-			return append(s[:index], s[index+1:]...)
+			// Using the provided slice as the basis for the return value can
+			// result in confusing behaviour, see https://go.dev/play/p/EAtNw4lLugu
+			c := make([]string, len(s))
+			copy(c, s)
+			return append(c[:index], c[index+1:]...)
 		}
 	}
 

strutil/strutil_test.go

@@ -46,6 +46,13 @@ func TestStrListDelete(t *testing.T) {
 	if StrListContains(output, "item3") {
 		t.Fatal("bad: 'item3' should not have been present")
 	}
+
+	// Test that StrListDelete doesn't modify its input
+	input := []string{"a", "b", "c"}
+	output = StrListDelete(input, "b")
+	if !reflect.DeepEqual(input, []string{"a", "b", "c"}) {
+		t.Fatal("bad: input modified")
+	}
 }
 
 func TestEquivalentSlices(t *testing.T) {