fix: group core files under their pack path

On a platform that writes bios/ in front of its destinations (RetroDECK, AmberELEC, EmuELEC), a core extra was grouped, dropped and held under its bare destination while the platform's declaration of the same file used bios/<name>. Beetle PSX's scph5501.bin was kept by the --region japan pack while the declaration was dropped and the installer dropped the path. extra_region_key keys every extra with the platform's declared root, in the builder, the manifest selection, verify's replay and the omissions. The same key gives the declared entries the systems of the core files at their path: every --system case of RetroDECK differed between pack and installer before, none does now.

tests/test_install_selection.py

@@ -1148,6 +1148,99 @@ class AStandaloneLayoutBelowTheBiosFolder(unittest.TestCase):
         self.assertEqual({f["dest"] for f in files}, {f["dest"] for f in built["files"]})
 
 
+class AnExtraBesideItsDeclarationBelowTheBiosFolder(unittest.TestCase):
+    """RetroDECK declares bios/scph5501.bin and writes core files below bios/.
+    Beetle PSX's scph5501.bin was grouped bare, a key whose region lookup
+    another core leaves untagged, while the declaration's key resolved to
+    DuckStation's American tag: `--region japan` dropped the declaration and
+    the pack kept the file through the core's claim, while the installer,
+    which records the path once, dropped it."""
+
+    def setUp(self):
+        import common
+        import generate_db
+        import generate_pack
+
+        self.gp = generate_pack
+        tmp = tempfile.TemporaryDirectory(dir=REPO_ROOT / "tmp")
+        self.addCleanup(tmp.cleanup)
+        previous = os.getcwd()
+        os.chdir(tmp.name)
+        self.addCleanup(os.chdir, previous)
+        Path("bios/Sys").mkdir(parents=True)
+        files = {}
+        for name in ("us.bin", "jp.bin"):
+            payload = name.encode()
+            Path(f"bios/Sys/{name}").write_bytes(payload)
+            sha1 = hashlib.sha1(payload).hexdigest()
+            files[sha1] = {"path": f"bios/Sys/{name}", "name": name,
+                           "size": len(payload), "sha1": sha1,
+                           "md5": hashlib.md5(payload).hexdigest(),
+                           "sha256": hashlib.sha256(payload).hexdigest(),
+                           "crc32": "00000001"}
+        self.db = {"files": files, "indexes": generate_db.build_indexes(files, {})}
+        Path("platforms").mkdir()
+        Path("platforms/p.yml").write_text(json.dumps({
+            "platform": "P", "version": "2.1", "verification_mode": "existence",
+            "base_destination": "", "cores": ["beetle", "dsa", "other"],
+            "standalone_cores": ["dsa"], "systems": {"sys": {"files": [
+                {"name": name, "destination": f"bios/{name}", "required": False}
+                for name in ("us.bin", "jp.bin")
+            ]}},
+        }))
+        Path("platforms/_registry.yml").write_text(
+            json.dumps({"platforms": {"p": {"status": "active"}}})
+        )
+        Path("emulators").mkdir()
+        Path("emulators/dsa.yml").write_text(json.dumps({
+            "emulator": "dsa", "type": "standalone + libretro", "systems": ["sys"],
+            "files": [
+                {"name": name, "standalone_path": f"bios/{name}", "system": "sys",
+                 "region": [region_name], "required": False}
+                for name, region_name in (("us.bin", "north-america"), ("jp.bin", "japan"))
+            ]}))
+        # Read before dsa, as beetle_psx is before duckstation, and untagged
+        # by name through a second reader, as pcsx1 leaves scph5501.bin.
+        Path("emulators/beetle.yml").write_text(json.dumps({
+            "emulator": "beetle", "type": "libretro", "systems": ["sys"], "files": [
+                {"name": "us.bin", "system": "sys", "region": ["north-america"],
+                 "required": False},
+            ]}))
+        Path("emulators/other.yml").write_text(json.dumps({
+            "emulator": "other", "type": "libretro", "systems": ["sys"], "files": [
+                {"name": "us.bin", "path": "alt/us.bin", "system": "sys", "required": False},
+            ]}))
+        common._platform_config_cache.clear()
+        common._emulator_profiles_cache.clear()
+        self.addCleanup(common._platform_config_cache.clear)
+        self.addCleanup(common._emulator_profiles_cache.clear)
+        self.profiles = common.load_emulator_profiles("emulators")
+
+    def _manifest(self, regions):
+        return self.gp.generate_manifest(
+            "p", "platforms", self.db, "bios", "platforms/_registry.yml",
+            emulators_dir="emulators", emu_profiles=self.profiles,
+            regions=regions, offline=True,
+        )
+
+    def _pack(self, regions):
+        record = self.gp.PackRecord()
+        self.gp.generate_pack(
+            "p", "platforms", self.db, "bios", "", emulators_dir="emulators",
+            emu_profiles=self.profiles, regions=regions, offline=True, record=record,
+        )
+        return {m for m in record.members if m.startswith("bios/")}
+
+    def test_the_pack_and_the_installer_drop_the_same_files(self):
+        full = self._manifest(None)
+        files, _omitted = install.narrow(
+            full["files"], full["omitted_files"], [], [], ["japan"]
+        )
+        installed = {f["dest"] for f in files if f["dest"].startswith("bios/")}
+        self.assertIn("bios/jp.bin", installed)
+        self.assertEqual(self._pack(["japan"]), installed)
+
+
 class ACoreWithNothingHeldIsAnOmission(unittest.TestCase):
     """DOSBox serves SC-55/WAVEROM3.BIN, DOSBox Pure wants it and nothing is
     held for it. A pack built for a target without DOSBox lists it as left