Merge changes I91063ebb,Id859723b

* changes:
  Differentiate between empty and nil input
  Do not modify input in-place

android/apex.go

@@ -513,9 +513,8 @@ func (m *ApexModuleBase) checkApexAvailableProperty(mctx BaseModuleContext) {
 // exactly the same set of APEXes (and platform), i.e. if their apex_available
 // properties have the same elements.
 func AvailableToSameApexes(mod1, mod2 ApexModule) bool {
-	// Use CopyOf to prevent non-determinism (b/275313114#comment1)
-	mod1ApexAvail := SortedUniqueStrings(CopyOf(mod1.apexModuleBase().ApexProperties.Apex_available))
-	mod2ApexAvail := SortedUniqueStrings(CopyOf(mod2.apexModuleBase().ApexProperties.Apex_available))
+	mod1ApexAvail := SortedUniqueStrings(mod1.apexModuleBase().ApexProperties.Apex_available)
+	mod2ApexAvail := SortedUniqueStrings(mod2.apexModuleBase().ApexProperties.Apex_available)
 	if len(mod1ApexAvail) != len(mod2ApexAvail) {
 		return false
 	}

android/util.go

@@ -26,7 +26,11 @@ import (
 
 // CopyOf returns a new slice that has the same contents as s.
 func CopyOf(s []string) []string {
-	return append([]string(nil), s...)
+	// If the input is nil, return nil and not an empty list
+	if s == nil {
+		return s
+	}
+	return append([]string{}, s...)
 }
 
 // Concat returns a new slice concatenated from the two input slices. It does not change the input
@@ -276,6 +280,8 @@ func RemoveFromList(s string, list []string) (bool, []string) {
 // FirstUniqueStrings returns all unique elements of a slice of strings, keeping the first copy of
 // each.  It modifies the slice contents in place, and returns a subslice of the original slice.
 func FirstUniqueStrings(list []string) []string {
+	// Do not moodify the input in-place, operate on a copy instead.
+	list = CopyOf(list)
 	// 128 was chosen based on BenchmarkFirstUniqueStrings results.
 	if len(list) > 128 {
 		return firstUniqueStringsMap(list)
@@ -332,6 +338,7 @@ func LastUniqueStrings(list []string) []string {
 
 // SortedUniqueStrings returns what the name says
 func SortedUniqueStrings(list []string) []string {
+	// FirstUniqueStrings creates a copy of `list`, so the input remains untouched.
 	unique := FirstUniqueStrings(list)
 	sort.Strings(unique)
 	return unique

android/util_test.go

@@ -381,6 +381,14 @@ func TestRemoveFromList(t *testing.T) {
 	}
 }
 
+func TestCopyOfEmptyAndNil(t *testing.T) {
+	emptyList := []string{}
+	copyOfEmptyList := CopyOf(emptyList)
+	AssertBoolEquals(t, "Copy of an empty list should be an empty list and not nil", true, copyOfEmptyList != nil)
+	copyOfNilList := CopyOf(nil)
+	AssertBoolEquals(t, "Copy of a nil list should be a nil list and not an empty list", true, copyOfNilList == nil)
+}
+
 func ExampleCopyOf() {
 	a := []string{"1", "2", "3"}
 	b := CopyOf(a)