feat: add Editor.merge() delegate

Author: nathanjmcdougall

src/yamltrip/editor.py

@@ -151,6 +151,10 @@ def sync(self, *keys: KeyPart, value: Any) -> None:
         """Sync the value at path to match the desired value."""
         self._document = self.document.sync(*keys, value=value)
 
+    def merge(self, *keys: KeyPart, value: Any) -> None:
+        """Merge a value into the mapping at path without removing extra keys."""
+        self._document = self.document.merge(*keys, value=value)
+
     def find_index(self, *keys: KeyPart, where: dict[str, Any]) -> int | None:
         """Return the index of the first list item matching all key/value pairs."""
         return self.document.find_index(*keys, where=where)

tests/test_merge.py

@@ -1,3 +1,4 @@
+from yamltrip import edit
 from yamltrip.document import Document
 
 
@@ -74,3 +75,15 @@ def test_returns_self_when_subset(self):
         doc = Document("a: 1\nb: 2\nc: 3\n")
         doc2 = doc.merge(value={"a": 1, "b": 2})
         assert doc2 is doc
+
+
+class TestEditorMerge:
+    def test_editor_merge(self, tmp_path):
+        p = tmp_path / "test.yaml"
+        p.write_text("a: 1\nb: 2\n", encoding="utf-8")
+        with edit(p) as ed:
+            ed.merge(value={"a": 99, "c": 3})
+        result = p.read_text(encoding="utf-8")
+        assert "a: 99" in result
+        assert "b: 2" in result
+        assert "c: 3" in result