Merge pull request rails#49166 from aleksclark/ensure-identical-dump-files

ensure identical md5 sums for gzip schema cache

Author: byroot

activerecord/lib/active_record/connection_adapters/schema_cache.rb

@@ -471,6 +471,7 @@ def open(filename)
           File.atomic_write(filename) do |file|
             if File.extname(filename) == ".gz"
               zipper = Zlib::GzipWriter.new file
+              zipper.mtime = 0
               yield zipper
               zipper.flush
               zipper.close

activerecord/test/cases/connection_adapters/schema_cache_test.rb

@@ -334,6 +334,27 @@ def test_marshal_dump_and_load_with_gzip
         tempfile.unlink
       end
 
+      def test_gzip_dumps_identical
+        # Create an empty cache.
+        cache = new_bound_reflection
+
+        tempfile_a = Tempfile.new(["schema_cache-", ".dump.gz"])
+        # Dump it. It should get populated before dumping.
+        cache.dump_to(tempfile_a.path)
+        digest_a = Digest::MD5.file(tempfile_a).hexdigest
+        sleep(1) # ensure timestamp changes
+        tempfile_b = Tempfile.new(["schema_cache-", ".dump.gz"])
+        # Dump it. It should get populated before dumping.
+        cache.dump_to(tempfile_b.path)
+        digest_b = Digest::MD5.file(tempfile_b).hexdigest
+
+
+        assert_equal digest_a, digest_b
+      ensure
+        tempfile_a.unlink
+        tempfile_b.unlink
+      end
+
       def test_data_source_exist
         assert @cache.data_source_exists?("courses")
         assert_not @cache.data_source_exists?("foo")