Fix droiddoc handling of $(location ...)

Bug: 124218911
Test: make checkbuild
Change-Id: I4d9c52b40ce4e8b9ae07f557e079e4f101fbbe87
diff --git a/java/droiddoc.go b/java/droiddoc.go
index cbe6be6..787c4d7 100644
--- a/java/droiddoc.go
+++ b/java/droiddoc.go
@@ -695,14 +695,17 @@
 	j.sourcepaths = android.PathsForModuleSrc(ctx, j.properties.Local_sourcepaths)
 
 	j.argFiles = ctx.ExpandSources(j.properties.Arg_files, nil)
-	argFilesMap := map[string]android.Path{}
+	argFilesMap := map[string]string{}
+	argFileLabels := []string{}
 
-	for _, f := range j.argFiles {
-		if _, exists := argFilesMap[f.Rel()]; !exists {
-			argFilesMap[f.Rel()] = f
+	for _, label := range j.properties.Arg_files {
+		var paths = ctx.ExpandSources([]string{label}, nil)
+		if _, exists := argFilesMap[label]; !exists {
+			argFilesMap[label] = strings.Join(paths.Strings(), " ")
+			argFileLabels = append(argFileLabels, label)
 		} else {
 			ctx.ModuleErrorf("multiple arg_files for %q, %q and %q",
-				f, argFilesMap[f.Rel()], f.Rel())
+				label, argFilesMap[label], paths)
 		}
 	}
 
@@ -710,10 +713,11 @@
 	j.args, err = android.Expand(String(j.properties.Args), func(name string) (string, error) {
 		if strings.HasPrefix(name, "location ") {
 			label := strings.TrimSpace(strings.TrimPrefix(name, "location "))
-			if f, ok := argFilesMap[label]; ok {
-				return f.String(), nil
+			if paths, ok := argFilesMap[label]; ok {
+				return paths, nil
 			} else {
-				return "", fmt.Errorf("unknown location label %q", label)
+				return "", fmt.Errorf("unknown location label %q, expecting one of %q",
+					label, strings.Join(argFileLabels, ", "))
 			}
 		} else if name == "genDir" {
 			return android.PathForModuleGen(ctx).String(), nil