Fix JSONPatch.add

CHANGELOG.md

@@ -4,7 +4,17 @@
 
 **Fixes**
 
-- Fixed JSON pointers using negative indices. The JSON Pointer specification (RFC 6901) does not allow negative array indexes. We now raise a `JSONPointerIndexError` if a JSON Pointer attempts to resolve an array item with a negative index. See [#115](https://github.com/jg-rp/python-jsonpath/issues/115). For anyone needing JSON Pointers that support negative indexes, set `JSONPointer.min_int_index` to a suitably negative integer, like `JSONPointer.min_int_index = -(2**53) + 1`.
+- Fixed JSON pointers with negative indices.
+
+  Previously, negative indices were resolved against array-like values, but the JSON Pointer specification (RFC 6901) does not permit negative array indexes. We now raise a `JSONPointerIndexError` when a JSON Pointer attempts to resolve an array element using a negative index.
+
+  For users who require negative indices in JSON Pointers, you can set `JSONPointer.min_int_index` to a suitably negative integer, like `JSONPointer.min_int_index = -(2**53) + 1`.
+
+  See [#116](https://github.com/jg-rp/python-jsonpath/pull/116).
+
+- Fixed the JSON Patch `add` operation.
+
+  Previously, a `JSONPatchError` was raised when pointing to an array index equal to the array's length. Now we append to arrays in such cases. See [#117](https://github.com/jg-rp/python-jsonpath/issues/117).
 
 ## Version 2.0.0
 

jsonpath/patch.py

@@ -7,6 +7,7 @@
 from abc import ABC
 from abc import abstractmethod
 from io import IOBase
+from typing import Any
 from typing import Dict
 from typing import Iterable
 from typing import List
@@ -70,7 +71,11 @@ def apply(
                 if target == "-":
                     parent.append(self.value)
                 else:
-                    raise JSONPatchError("index out of range")
+                    index = self.path._index(target)  # noqa: SLF001
+                    if index == len(parent):
+                        parent.append(self.value)
+                    else:
+                        raise JSONPatchError("index out of range")
             else:
                 parent.insert(int(target), self.value)
         elif isinstance(parent, MutableMapping):
@@ -628,7 +633,7 @@ def test(self: Self, path: Union[str, JSONPointer], value: object) -> Self:
 
     def apply(
         self,
-        data: Union[str, IOBase, MutableSequence[object], MutableMapping[str, object]],
+        data: Union[str, IOBase, MutableSequence[Any], MutableMapping[str, Any]],
     ) -> object:
         """Apply all operations from this patch to _data_.
 
@@ -676,7 +681,7 @@ def asdicts(self) -> List[Dict[str, object]]:
 
 def apply(
     patch: Union[str, IOBase, Iterable[Mapping[str, object]], None],
-    data: Union[str, IOBase, MutableSequence[object], MutableMapping[str, object]],
+    data: Union[str, IOBase, MutableSequence[Any], MutableMapping[str, Any]],
     *,
     unicode_escape: bool = True,
     uri_decode: bool = False,

tests/test_issues.py

@@ -1,5 +1,7 @@
 import pytest
 
+from jsonpath import JSONPatch
+from jsonpath import JSONPatchError
 from jsonpath import JSONPointerIndexError
 from jsonpath import findall
 from jsonpath import pointer
@@ -100,3 +102,16 @@ def test_issue_115() -> None:
     # Negative index
     with pytest.raises(JSONPointerIndexError):
         pointer.resolve("/users/-1/score", data)
+
+
+def test_issue_117() -> None:
+    # When the target value is an array of length 2, /foo/2 is the same as /foo/-
+    patch = JSONPatch().add(path="/foo/2", value=99)
+    data = {"foo": ["bar", "baz"]}
+    assert patch.apply(data) == {"foo": ["bar", "baz", 99]}
+
+    # Array length + 1 raises
+    patch = JSONPatch().add(path="/foo/3", value=99)
+    data = {"foo": ["bar", "baz"]}
+    with pytest.raises(JSONPatchError):
+        patch.apply(data)