Don't silently alter zip files opened with Zip::sort_entries.

Fixes rubyzip#329.

Changelog.md

@@ -1,5 +1,6 @@
 # 3.0.0 (Next)
 
+- Don't silently alter zip files opened with `Zip::sort_entries`. [#329](https://github.com/rubyzip/rubyzip/issues/329)
 - Use named parameters for optional arguments in the public API.
 - Raise an error if entry names exceed 65,535 characters. [#247](https://github.com/rubyzip/rubyzip/issues/247)
 - Remove the `ZipXError` v1 legacy classes.

README.md

@@ -132,9 +132,9 @@ class ZipFileGenerator
 end
 ```
 
-### Save zip archive entries in sorted by name state
+### Save zip archive entries sorted by name
 
-To save zip archives in sorted order like below, you need to set `::Zip.sort_entries` to `true`
+To save zip archives with their entries sorted by name (see below), set `::Zip.sort_entries` to `true`
 
 ```
 Vegetable/
@@ -148,7 +148,7 @@ fruit/mango
 fruit/orange
 ```
 
-After this, entries in the zip archive will be saved in ordered state.
+Opening an existing zip file with this option set will not change the order of the entries automatically. Altering the zip file - adding an entry, renaming an entry, adding or changing the archive comment, etc - will cause the ordering to be applied when closing the file.
 
 ### Default permissions of zip archives
 

lib/zip/entry_set.rb

@@ -35,10 +35,8 @@ def delete(entry)
       entry if @entry_set.delete(to_key(entry))
     end
 
-    def each
-      @entry_set = sorted_entries.dup.each do |_, value|
-        yield(value)
-      end
+    def each(&block)
+      entries.each(&block)
     end
 
     def entries

test/entry_set_test.rb

@@ -62,9 +62,15 @@ def test_each
     count = 0
     @zip_entry_set.each do |entry|
       assert(ZIP_ENTRIES.include?(entry))
+      refute(entry.dirty)
+      entry.dirty = true # Check that entries can be changed in this block.
       count += 1
     end
+
     assert_equal(ZIP_ENTRIES.size, count)
+    @zip_entry_set.each do |entry|
+      assert(entry.dirty)
+    end
   end
 
   def test_entries
@@ -101,6 +107,14 @@ def test_entries_sorted_in_each
       arr << entry
     end
     assert_equal(ZIP_ENTRIES.sort, arr)
+
+    # Ensure `each` above hasn't permanently altered the ordering.
+    ::Zip.sort_entries = false
+    arr = []
+    @zip_entry_set.each do |entry|
+      arr << entry
+    end
+    assert_equal(ZIP_ENTRIES, arr)
   end
 
   def test_compound