fix: prefer among the entries a reduced pack keeps

scripts/generate_pack.py

@@ -723,10 +723,13 @@ def generate_pack(
 
     preferred_entries: dict[str, int] = {}
     if source != "truth":
-        # A manifest lists the full set and carries no data directories, so
+        # Decided among the declarations this pack keeps: a preferred entry
-        # the preference is resolved with neither narrowing nor a cache.
+        # that --required-only drops must not silence its required twin, or
+        # the destination leaves the pack without a trace (RetroDECK's four
+        # Atari 5200 ROMs, optional under atari-400-800 and required under
+        # atari-5200). No data directories: the choice is about the baseline.
         preferred_entries = _preferred_entries(
-            pack_systems, db, bios_dir, base_dest, False,
+            pack_systems, db, bios_dir, base_dest, required_only,
             zip_contents, None, offline,
         )
 
@@ -3187,10 +3190,10 @@ def generate_manifest(
         # constrained sibling claim it; without the same rule here the
         # manifest named whatever answered to the name, so the pack and the
         # installer disagreed about which file a destination means.
-        # A manifest lists the full set and carries no data directories, so
+        # Decided among the declarations this manifest keeps, as the pack
-        # the preference is resolved with neither narrowing nor a cache.
+        # does; a manifest carries no data directories.
         preferred_entries = _preferred_entries(
-            pack_systems, db, bios_dir, base_dest, False,
+            pack_systems, db, bios_dir, base_dest, required_only,
             zip_contents, None, offline,
         )
         for sys_id, system in sorted(pack_systems.items()):

tests/test_required_only_twins.py

@@ -0,0 +1,103 @@
+"""A required declaration is never silenced by its optional twin.
+
+RetroDECK declares the four Atari 5200 ROMs optional under atari-400-800 and
+required under atari-5200, same md5. The preferred declaration for a shared
+destination was chosen over the full set, then applied to a loop that had
+already dropped the optional entries: under --required-only the preferred
+(optional) entry was skipped for being optional and the required one for not
+being preferred, and the destination left the pack, the status counts and
+the manifest without a trace.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import sys
+import tempfile
+import unittest
+import zipfile
+from pathlib import Path
+
+import yaml
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+sys.path.insert(0, str(REPO_ROOT / "scripts"))
+
+import common  # noqa: E402
+import generate_db  # noqa: E402
+import generate_pack as builder  # noqa: E402
+
+
+class RequiredTwins(unittest.TestCase):
+    def setUp(self):
+        self._tmp = tempfile.TemporaryDirectory()
+        self.root = Path(self._tmp.name)
+        self.bios = self.root / "bios" / "Atari"
+        self.platforms = self.root / "platforms"
+        self.emulators = self.root / "emulators"
+        for directory in (self.bios, self.platforms, self.emulators):
+            directory.mkdir(parents=True)
+        payload = b"atari os"
+        (self.bios / "ATARIOSB.ROM").write_bytes(payload)
+        md5 = hashlib.md5(payload).hexdigest()
+        sha1 = hashlib.sha1(payload).hexdigest()
+        files = {
+            sha1: {
+                "path": str(self.bios / "ATARIOSB.ROM"), "name": "ATARIOSB.ROM",
+                "size": len(payload), "sha1": sha1, "md5": md5,
+                "sha256": hashlib.sha256(payload).hexdigest(), "crc32": "00000008",
+            }
+        }
+        self.db = {"files": files, "indexes": generate_db.build_indexes(files, {})}
+        platform = {
+            "platform": "Twins",
+            "verification_mode": "md5",
+            "base_destination": "bios",
+            "cores": [],
+            "systems": {
+                # Sorted first: the optional declaration is the preferred one.
+                "atari-400-800": {"files": [
+                    {"name": "ATARIOSB.ROM", "destination": "ATARIOSB.ROM",
+                     "md5": md5, "required": False},
+                ]},
+                "atari-5200": {"files": [
+                    {"name": "ATARIOSB.ROM", "destination": "ATARIOSB.ROM",
+                     "md5": md5, "required": True},
+                ]},
+            },
+        }
+        (self.platforms / "twins.yml").write_text(yaml.dump(platform))
+        (self.platforms / "_registry.yml").write_text(
+            yaml.dump({"platforms": {"twins": {"status": "active"}}})
+        )
+        common._platform_config_cache.clear()
+        common._emulator_profiles_cache.clear()
+
+    def tearDown(self):
+        common._platform_config_cache.clear()
+        self._tmp.cleanup()
+
+    def test_the_required_only_pack_carries_the_required_file(self):
+        out = self.root / "dist"
+        out.mkdir()
+        zip_path = builder.generate_pack(
+            "twins", str(self.platforms), self.db, str(self.root / "bios"), str(out),
+            emulators_dir=str(self.emulators), emu_profiles={},
+            required_only=True, offline=True,
+        )
+        with zipfile.ZipFile(zip_path) as archive:
+            self.assertIn("ATARIOSB.ROM", archive.namelist())
+
+    def test_the_required_only_manifest_lists_it(self):
+        manifest = builder.generate_manifest(
+            "twins", str(self.platforms), self.db, str(self.root / "bios"),
+            str(self.platforms / "_registry.yml"),
+            emulators_dir=str(self.emulators), emu_profiles={},
+            required_only=True, offline=True,
+        )
+        listed = {entry["dest"] for entry in manifest["files"]}
+        self.assertIn("ATARIOSB.ROM", listed)
+
+
+if __name__ == "__main__":
+    unittest.main()