ResourcePathShortener deterministically handles hash collisions

ResourcePathShortener appends one digit at the end of colliding short
file names to disambiguate them. This cl sorts the list of file paths so
that colliding files always get the same disambiguating digit from one
run to the next rather than possibly alternating.

Test: make aapt2_tests

Change-Id: I983a1448c21f2c79d7cdb1de232e7758c04fc256

1 files changed, 11 insertions, 1 deletions

diff --git a/tools/aapt2/optimize/ResourcePathShortener.cpp b/tools/aapt2/optimize/ResourcePathShortener.cpp
index 7f5d10475f93..7ff9bf5aa8df 100644
--- a/tools/aapt2/optimize/ResourcePathShortener.cpp
+++ b/tools/aapt2/optimize/ResourcePathShortener.cpp
@@ -16,6 +16,7 @@
 
 #include "optimize/ResourcePathShortener.h"
 
+#include <set>
 #include <unordered_set>
 
 #include "androidfw/StringPiece.h"
@@ -71,10 +72,19 @@ std::string GetShortenedPath(const android::StringPiece& shortened_filename,
   return shortened_path;
 }
 
+// implement custom comparator of FileReference pointers so as to use the
+// underlying filepath as key rather than the integer address. This is to ensure
+// determinism of output for colliding files.
+struct PathComparator {
+    bool operator() (const FileReference* lhs, const FileReference* rhs) const {
+        return lhs->path->compare(*rhs->path);
+    }
+};
+
 bool ResourcePathShortener::Consume(IAaptContext* context, ResourceTable* table) {
   // used to detect collisions
   std::unordered_set<std::string> shortened_paths;
-  std::unordered_set<FileReference*> file_refs;
+  std::set<FileReference*, PathComparator> file_refs;
   for (auto& package : table->packages) {
     for (auto& type : package->types) {
       for (auto& entry : type->entries) {