Add ConvertApexAvailableToTags

This is a more flexible version of ApexAvailableTags
that can be used for the aidl modules.

Bug: 260694842
Test: go test
Change-Id: Iddb15e737c19e95977f74e8c627d6044d8875746

android/mutator.go

@@ -709,24 +709,29 @@ func (t *topDownMutatorContext) CreateBazelTargetModuleWithRestrictions(
 // module and returns it as a list of keyed tags.
 func ApexAvailableTags(mod Module) bazel.StringListAttribute {
 	attr := bazel.StringListAttribute{}
-	tags := []string{}
 	// Transform specific attributes into tags.
 	if am, ok := mod.(ApexModule); ok {
 		// TODO(b/218841706): hidl_interface has the apex_available prop, but it's
 		// defined directly as a prop and not via ApexModule, so this doesn't
 		// pick those props up.
-		// TODO(b/260694842): This does not pick up aidl_interface.backend.ndk.apex_available.
-		for _, a := range am.apexModuleBase().ApexAvailable() {
-			tags = append(tags, "apex_available="+a)
-		}
-	}
-	if len(tags) > 0 {
-		// This avoids creating a tags attr with an empty list if there are no tags.
-		attr.Value = tags
+		attr.Value = ConvertApexAvailableToTags(am.apexModuleBase().ApexAvailable())
 	}
 	return attr
 }
 
+func ConvertApexAvailableToTags(apexAvailable []string) []string {
+	if len(apexAvailable) == 0 {
+		// We need nil specifically to make bp2build not add the tags property at all,
+		// instead of adding it with an empty list
+		return nil
+	}
+	result := make([]string, 0, len(apexAvailable))
+	for _, a := range apexAvailable {
+		result = append(result, "apex_available="+a)
+	}
+	return result
+}
+
 func (t *topDownMutatorContext) createBazelTargetModule(
 	bazelProps bazel.BazelTargetModuleProperties,
 	commonAttrs CommonAttributes,