RF: Use consistent code for legacy hack and updated sidecar generation

Co-authored-by: Mathias Goncalves <goncalves.mathias@gmail.com>

Author: effigies

niworkflows/interfaces/bids.py

@@ -653,7 +653,7 @@ def _run_interface(self, runtime):
                 }
             )
             if self._metadata:
-                out_file = self._results["out_file"][0]
+                out_file = Path(self._results["out_file"][0])
                 # 1.3.x hack
                 # For dtseries, we have been generating weird non-BIDS JSON files.
                 # We can safely keep producing them to avoid breaking derivatives, but
@@ -664,13 +664,10 @@ def _run_interface(self, runtime):
                         if key in self._metadata:
                             legacy_metadata[key] = self._metadata.pop(key)
                     if legacy_metadata:
-                        sidecar = Path(self._results["out_file"][0]).parent / (
-                            "%s.json" % _splitext(self._results["out_file"][0])[0]
-                        )
+                        sidecar = out_file.parent / f"{_splitext(str(out_file))[0]}.json"
                         sidecar.write_text(dumps(legacy_metadata, sort_keys=True, indent=2))
                 # The future: the extension is the first . and everything after
-                out_path = Path(out_file)
-                sidecar = out_path.parent / f"{out_path.name.split('.', 1)[0]}.json"
+                sidecar = out_file.parent / f"{out_file.name.split('.', 1)[0]}.json"
                 sidecar.write_text(dumps(self._metadata, sort_keys=True, indent=2))
                 self._results["out_meta"] = str(sidecar)
         return runtime