Preserve nested JSON objects when splitting frontmatter

frontmatter/default_handlers.py

@@ -283,9 +283,15 @@ class JSONHandler(BaseHandler):
     END_DELIMITER = ""
 
     def split(self, text: str) -> tuple[str, str]:
-        assert self.FM_BOUNDARY is not None
-        _, fm, content = self.FM_BOUNDARY.split(text, 2)
-        return "{" + fm + "}", content
+        try:
+            _, end = json.JSONDecoder().raw_decode(text)
+        except json.JSONDecodeError:
+            # Preserve existing malformed-frontmatter behavior: load() raises
+            # for invalid JSON with delimiters; missing boundaries stay content.
+            assert self.FM_BOUNDARY is not None
+            _, fm, content = self.FM_BOUNDARY.split(text, 2)
+            return "{" + fm + "}", content
+        return text[:end], text[end:]
 
     def load(self, fm: str, **kwargs: object) -> Any:
         return json.loads(fm, **kwargs)  # type: ignore[arg-type]

tests/test_nested_json.py

@@ -0,0 +1,24 @@
+import json
+
+import pytest
+
+import frontmatter
+from frontmatter.default_handlers import JSONHandler
+
+
+@pytest.mark.parametrize('metadata', [
+    {'outer': {'inner': 1}, 'title': 'Example'},
+    {'items': [{'title': 'first'}, {'title': 'second'}]},
+    {'quoted': '} and {', 'nested': {'text': 'escaped " quote'}},
+])
+def test_nested_unindented_json_round_trip(metadata):
+    post = frontmatter.Post('Body\n\n{content stays content}', JSONHandler(), **metadata)
+    text = frontmatter.dumps(post, indent=0)
+    restored = frontmatter.loads(text)
+    assert restored.metadata == metadata
+    assert restored.content == post.content
+
+
+def test_malformed_delimited_json_still_raises():
+    with pytest.raises(json.JSONDecodeError):
+        frontmatter.loads('{\n"title": invalid\n}\n\nBody')