fix: refuse an unparseable platform original

scripts/exporter/recalbox_exporter.py

@@ -131,8 +131,13 @@ class Exporter(BaseExporter):
         if original:
             try:
                 root = parse_untrusted_xml(original, self.native_filename(), comments=True)
-            except (ParseError, ValueError):
-                root = None
+            except (ParseError, ValueError) as exc:
+                # Rebuilt from our model alone, the export would drop every
+                # system we do not transcribe and the maintainer's comments.
+                raise ValueError(
+                    f"Recalbox's {self.native_filename()} does not parse ({exc}); "
+                    "fetch it again with --refresh-cache"
+                ) from exc
             if root is not None:
                 theirs = [
                     (s.get("platform", ""), s.get("fullname", ""), [

scripts/exporter/retrobat_exporter.py

@@ -69,8 +69,11 @@ class Exporter(BaseExporter):
         if original:
             try:
                 base = json.loads(original, object_pairs_hook=OrderedDict)
-            except json.JSONDecodeError:
-                base = {}
+            except json.JSONDecodeError as exc:
+                raise ValueError(
+                    f"RetroBat's {self.native_filename()} does not parse ({exc}); "
+                    "fetch it again with --refresh-cache"
+                ) from exc
 
         exportable = {
             system.native_id: (system, files)

tests/test_export_counts.py

@@ -762,5 +762,29 @@ class AStaleTruthIsRefused(unittest.TestCase):
             export_native.load_inputs("retropie", truth_dir, str(root / "platforms"))
 
 
+
+class ACorruptOriginalIsRefused(unittest.TestCase):
+    """A truncated es_bios.xml in the cache was ignored: the export was
+    rebuilt from our model alone, losing the systems we do not transcribe
+    and the maintainer's comments, and the run ended in success."""
+
+    def test_recalbox_refuses_it(self):
+        fe = NativeFile("bios.bin", "bios.bin", "nes", platform={"md5": A})
+        exporter = Recalbox()
+        with self.assertRaises(ValueError) as caught:
+            exporter.render({"nes": NativeSystem("nes", files=[fe])}, None,
+                            {exporter.native_filename(): "<biosList><system platform="})
+        self.assertIn("does not parse", str(caught.exception))
+
+    def test_retrobat_refuses_it(self):
+        from exporter.retrobat_exporter import Exporter as RetroBat  # noqa: PLC0415
+
+        fe = NativeFile("bios.bin", "bios.bin", "nes", platform={"md5": A})
+        exporter = RetroBat()
+        with self.assertRaises(ValueError):
+            exporter.render({"nes": NativeSystem("nes", files=[fe])}, None,
+                            {exporter.native_filename(): '{"nes": {'})
+
+
 if __name__ == "__main__":
     unittest.main()