fix: refuse profile narrowings without cores

MiSTer and BizHawk declare cores: []. --region, --one-per-slot and
--no-game-data read the profiles of the cores a platform runs, so their
packs and manifests withdrew nothing under a name and README that said
they had. generate_pack and verify now refuse the flags for a named
platform and leave it out under --all.

platforms/_registry.yml

@@ -1011,7 +1011,9 @@ platforms:
     # EmuHawk finds firmware by SHA1 against FirmwareDatabase.FirmwareRecords
     # and its cores are its own builds (CoreNames.cs): no libretro profile
     # describes what it reads, so the database alone decides, as MiSTer's
-    # BiosDB does.
+    # BiosDB does. emulators/bizhawk.yml also documents the options the scan
+    # never takes, so it is not listed here, and --region, --one-per-slot
+    # and --no-game-data are refused for this platform.
     cores: []
     target_scraper: null
     target_source: null

scripts/common.py

@@ -2761,6 +2761,29 @@ def preferred_profile(index: dict[str, set[str]], name: str) -> str | None:
     return name if name in claimants else sorted(claimants)[0]
 
 
+def profile_blind_platforms(
+    platforms: list[str],
+    platforms_dir: str,
+    profiles: dict[str, dict],
+    target_cores: dict[str, set[str] | None] | None = None,
+) -> list[str]:
+    """Platforms that run no core a profile describes.
+
+    Regions, search order and game data are read from the profiles of the
+    cores a platform runs. MiSTer and BizHawk declare `cores: []`: a
+    --region, --one-per-slot or --no-game-data pack of theirs withdrew
+    nothing while its name and README said it had.
+    """
+    return [
+        name for name in platforms
+        if not resolve_platform_cores(
+            load_platform_config(name, platforms_dir),
+            profiles,
+            target_cores=(target_cores or {}).get(name),
+        )
+    ]
+
+
 def resolve_platform_cores(
     config: dict,
     profiles: dict[str, dict],

scripts/generate_pack.py

@@ -75,6 +75,7 @@ from common import (
     load_database,
     load_emulator_profiles,
     load_platform_config,
+    profile_blind_platforms,
     MANUFACTURER_PREFIXES,
     require_yaml,
     ProfileSelectionError,
@@ -3074,6 +3075,42 @@ def _pack_label(source: str, required_only: bool) -> str:
     return f"[source={source}, required]" if required_only else f"[source={source}]"
 
 
+def _without_profile_blind(
+    args: argparse.Namespace,
+    platforms: list[str],
+    emu_profiles: dict,
+    target_cores_cache: dict[str, set[str] | None],
+) -> list[str]:
+    """Refuse a narrowing read from profiles on a platform that runs none.
+
+    Named, the platform is refused. Under --all it is left out with a
+    notice, as an empty truth pack is under --all-variants.
+    """
+    flags = [
+        flag for flag, given in (
+            ("--region", getattr(args, "regions", None)),
+            ("--one-per-slot", getattr(args, "one_per_slot", False)),
+            ("--no-game-data", getattr(args, "no_game_data", False)),
+        ) if given
+    ]
+    if not flags:
+        return platforms
+    blind = profile_blind_platforms(
+        platforms, args.platforms_dir, emu_profiles,
+        target_cores_cache if args.target else None,
+    )
+    for name in blind:
+        message = (
+            f"{name} runs no core a profile describes, and {', '.join(flags)} "
+            "reads the profiles"
+        )
+        if not args.all:
+            print(f"ERROR: {message}: drop {', '.join(flags)}", file=sys.stderr)
+            sys.exit(1)
+        print(f"  {message}: left out")
+    return [name for name in platforms if name not in blind]
+
+
 def _truth_layer_is_empty(
     platform: str, platforms_dir: str, emu_profiles: dict, target_cores: set[str] | None
 ) -> bool:
@@ -3785,6 +3822,9 @@ def _main(held: contextlib.ExitStack) -> None:
         platforms = _platforms_with_systems(
             args, platforms, system_filter, emu_profiles, target_cores_cache
         )
+    platforms = _without_profile_blind(
+        args, platforms, emu_profiles, target_cores_cache
+    )
 
     data_registry = load_data_dir_registry(args.platforms_dir)
     # The output directory is claimed before the data directory refresh: a

scripts/verify.py

@@ -65,6 +65,7 @@ from common import (
     load_database,
     load_emulator_profiles,
     load_platform_config,
+    profile_blind_platforms,
     resolve_system_arg,
     print_platform_listing,
     select_systems,
@@ -3017,6 +3018,30 @@ def _main(held: contextlib.ExitStack) -> None:
                 print(f"ERROR: {reason}", file=sys.stderr)
                 sys.exit(1)
 
+    # generate_pack refuses these on a platform whose cores no profile
+    # describes, and the report answers the same request the same way.
+    flags = [
+        flag for flag, given in (
+            ("--region", requested_regions),
+            ("--no-game-data", getattr(args, "no_game_data", False)),
+        ) if given
+    ]
+    if flags:
+        blind = profile_blind_platforms(
+            platforms, args.platforms_dir, emu_profiles,
+            target_cores_cache if args.target else None,
+        )
+        for name in blind:
+            message = (
+                f"{name} runs no core a profile describes, and "
+                f"{', '.join(flags)} reads the profiles"
+            )
+            if not args.all:
+                print(f"ERROR: {message}: drop {', '.join(flags)}", file=sys.stderr)
+                sys.exit(1)
+            print(f"  {message}: left out")
+        platforms = [name for name in platforms if name not in blind]
+
     # Group identical platforms (same function as generate_pack)
     groups = group_identical_platforms(
         platforms, args.platforms_dir, target_cores_cache if args.target else None

tests/test_e2e.py

@@ -6374,6 +6374,33 @@ struct BurnDriver BurnDrvneogeo = {
             [f for f in os.listdir(out) if f.endswith(".zip")] if os.path.isdir(out) else []
         )
 
+    def test_a_platform_without_cores_refuses_profile_narrowings(self):
+        """MiSTer and BizHawk declare cores: []. --region, --one-per-slot
+        and --no-game-data read the profiles, so their packs withdrew
+        nothing under a name and README that said otherwise."""
+        import subprocess
+
+        repo = os.path.join(os.path.dirname(__file__), "..")
+        out = os.path.join(self.root, "blind")
+        runs = [
+            ["scripts/generate_pack.py", "--platform", "misterfpga", "--region", "us"],
+            ["scripts/generate_pack.py", "--platform", "misterfpga", "--one-per-slot"],
+            ["scripts/generate_pack.py", "--platform", "misterfpga", "--no-game-data"],
+            ["scripts/generate_pack.py", "--platform", "bizhawk", "--manifest",
+             "--region", "us"],
+            ["scripts/verify.py", "--platform", "bizhawk", "--region", "us"],
+        ]
+        for argv in runs:
+            extra = ["--offline", "--output-dir", out] if "generate_pack" in argv[0] else []
+            with self.subTest(argv=argv):
+                proc = subprocess.run(
+                    [sys.executable, *argv, *extra],
+                    capture_output=True, text=True, cwd=repo, timeout=300,
+                )
+                self.assertEqual(proc.returncode, 1, proc.stdout + proc.stderr)
+                self.assertIn("runs no core a profile describes", proc.stderr)
+        self.assertFalse(os.listdir(out) if os.path.isdir(out) else [])
+
     def test_a_full_pack_is_not_announced_as_narrowed(self):
         from generate_pack import _build_readme, _narrowings
 

wiki/advanced-usage.md

@@ -140,6 +140,11 @@ Three rules keep a filtered pack usable:
 - **Untagged files always survive.** Most BIOS are not regional and carry no
   `region:` at all.
 
+Regions, the search order `--one-per-slot` reads and the game data
+`--no-game-data` cuts all come from the profiles of the cores a platform runs.
+MiSTer and BizHawk declare no cores, their own databases decide, so the three
+flags are refused for them. Under `--all` they are left out with a notice.
+
 What this does and does not do: it shrinks the pack. It does not change how cores
 pick a BIOS. Most cores already select per region from fixed filename lists driven
 by the game's region (PicoDrive in `libretro.c`, Genesis Plus GX in `loadrom.c`),