Do not set variable GZip#mtime but do always set File#mtime

lib/sprockets/encoding_utils.rb

@@ -50,6 +50,8 @@ def unmarshaled_deflated(str, window_bits = -Zlib::MAX_WBITS)
       Marshal.load(marshaled)
     end
 
+    GZIP_MTIME = RUBY_VERSION >= "2.7" ? 0 : 1
+
     # Public: Use gzip to compress data.
     #
     # str - String data
@@ -58,7 +60,7 @@ def unmarshaled_deflated(str, window_bits = -Zlib::MAX_WBITS)
     def gzip(str)
       io = StringIO.new
       gz = Zlib::GzipWriter.new(io, Zlib::BEST_COMPRESSION)
-      gz.mtime = 1
+      gz.mtime = Sprockets::EncodingUtils::GZIP_MTIME
       gz << str
       gz.finish
       io.string

lib/sprockets/utils/gzip.rb

@@ -10,13 +10,15 @@ class Gzip
       # writes contents to the `file` passed in. Sets `mtime` of
       # written file to passed in `mtime`
       module ZlibArchiver
-        def self.call(file, source, mtime)
+        MTIME = RUBY_VERSION >= "2.7" ? 0 : 1
+
+        def self.call(file, source)
           gz = Zlib::GzipWriter.new(file, Zlib::BEST_COMPRESSION)
-          gz.mtime = mtime
+          gz.mtime = MTIME
           gz.write(source)
           gz.close
 
-          File.utime(mtime, mtime, file.path)
+          nil
         end
       end
 
@@ -28,8 +30,8 @@ def self.call(file, source, mtime)
       # writes contents to the `file` passed in. Sets `mtime` of
       # written file to passed in `mtime`
       module ZopfliArchiver
-        def self.call(file, source, mtime)
-          compressed_source = Autoload::Zopfli.deflate(source, format: :gzip, mtime: mtime)
+        def self.call(file, source)
+          compressed_source = Autoload::Zopfli.deflate(source, format: :gzip)
           file.write(compressed_source)
           file.close
 
@@ -90,7 +92,8 @@ def cannot_compress?
       # Returns nothing.
       def compress(file, target)
         mtime = Sprockets::PathUtils.stat(target).mtime
-        archiver.call(file, source, mtime)
+        archiver.call(file, source)
+        File.utime(mtime, mtime, file.path)
 
         nil
       end

test/test_encoding_utils.rb

@@ -15,7 +15,7 @@ def test_deflate
   def test_gzip
     output = gzip("foobar")
     assert_equal 26, output.length
-    assert_equal [31, 139, 8, 0, 1, 0, 0, 0], output.bytes.take(8)
+    assert_equal [31, 139, 8, 0, Sprockets::EncodingUtils::GZIP_MTIME, 0, 0, 0], output.bytes.take(8)
   end
 
   def test_base64