fix: reduce emulator packs by region after required-only

scripts/generate_pack.py

@@ -1257,7 +1257,9 @@ def generate_emulator_pack(
     os.makedirs(output_dir, exist_ok=True)
 
     region_drops: set[str] = (
-        emulator_region_drops(selected, standalone, regions) if regions else set()
+        emulator_region_drops(selected, standalone, regions, required_only)
+        if regions
+        else set()
     )
 
     total_files = 0

scripts/packextras.py

@@ -709,7 +709,10 @@ def platform_region_groups(
     return groups, extra_dests
 
 def emulator_region_drops(
-    selected: list[tuple[str, dict]], standalone: bool, regions: list[str]
+    selected: list[tuple[str, dict]],
+    standalone: bool,
+    regions: list[str],
+    required_only: bool = False,
 ) -> set[str]:
     """Destinations an emulator-mode `--region` withdraws.
 
@@ -726,7 +729,10 @@ def emulator_region_drops(
     region_groups: dict[str, list[tuple[str, str]]] = {}
     for emu_name, profile in sorted(selected):
         structure = profile.get("pack_structure")
-        for fe in filter_files_by_mode(profile.get("files", []), standalone):
+        # Decided over what the pack keeps, as on the platform side: an
+        # optional winner removed afterwards left its slot empty.
+        entries = filter_files_by_mode(profile.get("files", []), standalone)
+        for fe in _kept(entries, required_only):
             dest = _resolve_destination(fe, structure, standalone)
             if dest:
                 group_id = _emulator_region_group(emu_name, profile, fe)

tests/test_region_required_only.py

@@ -42,5 +42,20 @@ class RequiredOnlyBeforeRegion(unittest.TestCase):
             self.assertIn("required_only", {kw.arg for kw in call.keywords})
 
 
+class EmulatorModeToo(unittest.TestCase):
+    """--emulator mednafen_pce_fast --region us --required-only shipped 0 files:
+    the optional US cards won the group, then --required-only removed them."""
+
+    def test_the_required_card_survives(self):
+        from packextras import emulator_region_drops  # noqa: PLC0415
+
+        profile = {"systems": ["nec-pc-engine"], "files": [
+            {"name": "syscard3.pce", "required": True, "region": ["japan"]},
+            {"name": "syscard3u.pce", "required": False, "region": ["north-america"]},
+        ]}
+        drops = emulator_region_drops([("pce", profile)], False, ["north-america"], True)
+        self.assertNotIn("syscard3.pce", drops)
+
+
 if __name__ == "__main__":
     unittest.main()