fix: group system-less files alike in both modes

scripts/packextras.py

@@ -1079,7 +1079,7 @@ def emulator_region_drops(
         for fe in _kept(entries, required_only):
             dest = _resolve_destination(fe, standalone)
             if dest:
-                group_id = _emulator_region_group(emu_name, profile, fe)
+                group_id = _emulator_region_group(emu_name, profile, fe, dest)
                 region_groups.setdefault(group_id, []).append(
                     (dest, fe.get("name", ""))
                 )
@@ -1090,8 +1090,16 @@ def emulator_region_drops(
     return region_mod.resolve_region_drops(region_groups, region_index, regions, held)
 
 
-def _emulator_region_group(emu_name: str, profile: dict, file_entry: dict) -> str:
+def _emulator_region_group(
-    """Stable group ID for regional alternatives within an emulator profile."""
+    emu_name: str, profile: dict, file_entry: dict, dest: str
+) -> str:
+    """Stable group ID for regional alternatives within an emulator profile.
+
+    The rule extra_region_groups applies on the platform side: a file no
+    system names, in a profile serving several, competes with nothing.
+    Grouped together, geargrafx's LaserActive pac-n1.bin was dropped by
+    --emulator --region us and kept by --platform --region us.
+    """
     variant = file_entry.get("variant_group")
     if variant:
         return f"{emu_name}:variant:{variant}"
@@ -1099,4 +1107,6 @@ def _emulator_region_group(emu_name: str, profile: dict, file_entry: dict) -> st
     profile_systems = list(profile.get("systems", []))
     if not system and len(profile_systems) == 1:
         system = profile_systems[0]
-    return f"{emu_name}:system:{system or '_profile'}"
+    if not system:
+        return f"{emu_name}:file:{dest}"
+    return f"{emu_name}:system:{system}"

tests/test_audit_regressions.py

@@ -1441,13 +1441,35 @@ class RegionRegressions(unittest.TestCase):
     def test_multi_system_emulator_uses_separate_region_groups(self):
         profile = {"systems": ["odyssey2", "videopac"]}
         north_america = _emulator_region_group(
-            "o2em", profile, {"name": "o2rom.bin", "system": "odyssey2"}
+            "o2em", profile, {"name": "o2rom.bin", "system": "odyssey2"}, "o2rom.bin"
         )
         europe = _emulator_region_group(
-            "o2em", profile, {"name": "c52.bin", "system": "videopac"}
+            "o2em", profile, {"name": "c52.bin", "system": "videopac"}, "c52.bin"
         )
         self.assertNotEqual(north_america, europe)
 
+    def test_a_systemless_file_groups_alike_in_both_modes(self):
+        """geargrafx files pac-n1.bin [japan] and pac-n10.bin [north-america]
+        under none of its four systems: emulator mode grouped them and
+        dropped pac-n1.bin for --region us, platform mode isolated each and
+        kept it."""
+        from packextras import extra_region_groups
+
+        profile = {"systems": ["nec-pc-engine", "nec-pc-engine-cd", "nec-supergrafx",
+                               "pioneer-laseractive"]}
+        names = ["pac-n1.bin", "pac-n10.bin"]
+        emulator = [
+            _emulator_region_group("geargrafx", profile, {"name": n}, n) for n in names
+        ]
+        platform = [
+            extra_region_groups({
+                "source_emulator": "geargrafx", "destination": n,
+                "source_systems": profile["systems"],
+            })[0]
+            for n in names
+        ]
+        self.assertEqual(emulator, platform)
+
     def test_region_audit_resolves_the_way_the_pack_does(self):
         """A private resolver read sha1, md5 and a lone name: an entry
         identified by its path (Dolphin's three IPL.bin) was never checked."""