Analyze list insertion/deletion optimization issue in JsonPatch

Co-authored-by: stefankoegl <184196+stefankoegl@users.noreply.github.com>

Author: Copilot

comprehensive_test.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+import unittest
+import jsonpatch
+import json
+
+class ComprehensiveOptimizationTest(unittest.TestCase):
+    def test_list_insertion_optimization(self):
+        """Test that list insertions are optimized correctly."""
+        test_cases = [
+            # Simple replacements - already work
+            (
+                {'foo': [1, 2, 3]}, 
+                {'foo': [1, 4, 3]}, 
+                "Simple element replacement"
+            ),
+            # Insertion and deletion (same index) - should be optimized to replace
+            (
+                [1, 2, 3, 4], 
+                [1, 5, 3, 4],
+                "Insert and remove at same index - should be replace"
+            ),
+            # Insertion at beginning, removal at end - might be optimized to replace
+            (
+                [1, 2, 3, 4], 
+                [5, 1, 2, 3],
+                "Insert at beginning, remove at end - could be optimized"
+            ),
+            # Insert and remove at different positions - harder to optimize
+            (
+                [1, 2, 3, 4], 
+                [1, 5, 2, 4],
+                "Insert and remove at different positions"
+            ),
+            # Multiple changes - complex case
+            (
+                [1, 2, 3, 4, 5], 
+                [1, 6, 2, 7, 5],
+                "Multiple replacements"
+            ),
+        ]
+        
+        for src, dst, msg in test_cases:
+            print(f"\nTesting: {msg}")
+            print(f"Source: {src}")
+            print(f"Destination: {dst}")
+            patch = list(jsonpatch.make_patch(src, dst))
+            print(f"Generated patch: {json.dumps(patch, indent=2)}")
+            # Verify that applying the patch produces the expected result
+            result = jsonpatch.apply_patch(src, patch)
+            self.assertEqual(result, dst)
+            print(f"Result after applying patch: {result}")
+            
+            # Count the operations
+            op_counts = {}
+            for op in patch:
+                op_type = op['op']
+                op_counts[op_type] = op_counts.get(op_type, 0) + 1
+                
+            print(f"Operation counts: {op_counts}")
+            print("-" * 50)
+            
+if __name__ == "__main__":
+    unittest.main()

test_failing.py

@@ -0,0 +1,30 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+import unittest
+import jsonpatch
+
+class FailingOptimizationTest(unittest.TestCase):
+    def test_list_replacement_optimization(self):
+        # A case where a list element is replaced with a new value
+        src = {'foo': [1, 2, 3]}
+        dst = {'foo': [1, 4, 3]}
+        patch = list(jsonpatch.make_patch(src, dst))
+        print("Patch:", patch)
+        self.assertEqual(len(patch), 1)
+        self.assertEqual(patch[0]['op'], 'replace')
+        self.assertEqual(patch[0]['path'], '/foo/1')
+        self.assertEqual(patch[0]['value'], 4)
+
+    def test_list_insertion_deletion(self):
+        # A case where elements are both inserted and deleted
+        src = [1, 2, 3, 4]
+        dst = [1, 5, 2, 4]
+        patch = list(jsonpatch.make_patch(src, dst))
+        print("Insertion/Deletion Patch:", patch)
+        # Expected: replace operation at index 1 and removal of index 2
+        # Instead of producing multiple operations
+        # The optimization should collapse sequential operations when possible
+        
+if __name__ == "__main__":
+    unittest.main()