fix: treat an empty platform system as named

scripts/exporter/baseline.py

@@ -265,6 +265,16 @@ def build_native_model(
     norm_to_scraped: dict[str, str] = {
         _norm_system_id(key): key for key in scraped_systems
     }
+    # Every system the platform names, files or none: an addition elsewhere
+    # is filed under our own slug.
+    platform_ids = {
+        native_id
+        for key, sys_data in scraped_systems.items()
+        for native_id in (
+            sys_data.get("native_id") or key,
+            *(_native_id_of(key, sys_data, fe) for fe in sys_data.get("files", [])),
+        )
+    }
     native_by_norm: dict[str, str] = {}
     for system in systems.values():
         native_by_norm.setdefault(_norm_system_id(system.native_id), system.native_id)
@@ -431,7 +441,7 @@ def build_native_model(
                     destination=destination,
                     native_system=native_id,
                     truth=truth_entry,
-                    foreign_system=not system.from_platform,
+                    foreign_system=native_id not in platform_ids,
                 )
             )
             report.files_added += 1

tests/test_exporters.py

@@ -917,6 +917,18 @@ class BatoceraExport(unittest.TestCase):
         )
         self.assertNotIn('"nintendo-snes"', produced["batocera-systems"])
 
+    def test_a_system_the_platform_names_without_files_is_its_own(self):
+        """A system the platform declares empty still has the platform's id."""
+        scraped = {"systems": {"nintendo-snes": {"native_id": "snes", "files": []}}}
+        truth = {"systems": {"nintendo-snes": {"files": [{
+            "name": "st010.zip", "path": "st010.zip", "md5": "2" * 32,
+            "required": False, "_cores": ["snes9x"],
+        }]}}}
+        systems, _ = build_native_model(truth, scraped)
+        (entry,) = systems["snes"].files
+        self.assertFalse(entry.foreign_system)
+        self.assertTrue(discover_exporters()["batocera"]().writable(entry))
+
     def test_writing_without_the_platform_file_is_refused(self):
         """A systems dict alone is not the script Batocera runs."""
         systems, report = model()