fix: never prove a file by another emulator's tree

lrps2 names no hash for its GameIndex.yaml, and the only full-tail
copy was ARMSX2's: it counted as path proof and replaced the file
RetroArch pins on desktop targets, which have no ARMSX2. Upstream
PCSX2 took ARMSX2's patches.zip by name the same way. A copy in
another emulator's tree now proves nothing at any tail length, and
LRPS2's own GameIndex comes from the tree the buildbot publishes.

emulators/lrps2.yml

@@ -19,6 +19,10 @@ bios_directory: "pcsx2/bios/"
 resources_directory: "pcsx2/resources/"
 
 notes: |
+  pcsx2/resources/GameIndex.yaml, the per-game patch, settings override and
+  compatibility database, is the one the buildbot publishes in LRPS2.zip (the
+  lrps2 data directory). An OSD warning is shown if it is missing; some games
+  do not boot without it.
   Hard fork of PCSX2 (pre-Qt, 1.7-dev era) ported to libretro. x86_64 only.
   BIOS detection is filename-agnostic: scans pcsx2/bios/ for any file between 4-8 MB
   with a valid romdir structure (RESET + ROMVER entries). No hash validation.
@@ -28,6 +32,11 @@ notes: |
   .info firmware_count=2 counts the bios folder and GameIndex.yaml.
   .info description mentions EROM.BIN but no EROM loading path exists in the code.
 
+data_directories:
+  - ref: lrps2
+    destination: ""
+    source_ref: "pcsx2/GameDatabase.cpp:49, pcsx2/GameDatabase.cpp:979"
+
 files:
   - name: "<bios>.bin"
     path: "pcsx2/bios/<bios>.bin"
@@ -85,15 +94,6 @@ files:
       Mechacon (disc drive controller) version as u32.
       Auto-created with default 0x00020603 if missing.
 
-  - name: "GameIndex.yaml"
-    path: "pcsx2/resources/GameIndex.yaml"
-    required: false
-    description: "game compatibility database"
-    source_ref: "pcsx2/GameDatabase.cpp:49, pcsx2/GameDatabase.cpp:979"
-    note: >
-      YAML database of per-game patches, settings overrides, and compatibility fixes.
-      OSD warning shown if missing. Some games may not boot or have issues without it.
-
   - name: "cheats_ws.zip"
     path: "pcsx2/resources/cheats_ws.zip"
     required: false

scripts/common.py

@@ -644,8 +644,8 @@ def _rank_tail_candidates(
 ) -> list[str]:
     """Order the files a destination tail designates, the likeliest first.
 
-    A shortened tail found only in another emulator's tree is that
-    emulator's asset, not evidence about this entry. A full tail claimed
+    A tail found in another emulator's tree is that emulator's asset, not
+    evidence about this entry, whatever its length. A full tail claimed
     twice goes to the file whose path carries the least on top of the
     destination, then to the owner's own copy (super3's Games.xml was served
     to Supermodel-Dojo by index order alone), then to any copy outside
@@ -655,8 +655,11 @@ def _rank_tail_candidates(
     def path_of(sha1: str) -> str:
         return files_db.get(sha1, {}).get("path", "")
 
-    if start:
-        candidates = [h for h in candidates if not _foreign_tree(path_of(h), owners)]
+    # Another emulator's tree answers that emulator's entry, at any tail
+    # length: lrps2 names no hash for pcsx2/resources/GameIndex.yaml, and the
+    # only full-tail copy was ARMSX2's, which then counted as path proof and
+    # replaced the GameIndex RetroArch pins on every desktop target.
+    candidates = [h for h in candidates if not _foreign_tree(path_of(h), owners)]
     if len(candidates) < 2:
         return candidates
     depth = len(tail.split("/"))
@@ -1040,6 +1043,13 @@ def resolve_local_file(
             if file_entry.get("members"):
                 candidates = _holding_members(candidates, file_entry["members"])
             candidates = _by_affinity(candidates, file_entry, dest_hint)
+            # A copy outside another emulator's tree comes first: the
+            # affinity read pcsx2 in bios/Other/armsx2/pcsx2/ and served
+            # upstream PCSX2 the patches.zip of ARMSX2.
+            owners = _owner_tokens(file_entry)
+            candidates = [
+                p for p in candidates if not _foreign_tree(p, owners)
+            ] or candidates
             primary = [p for p in candidates if "/.variants/" not in p]
             if primary or candidates:
                 chosen = primary[0] if primary else candidates[0]

tests/test_audit_regressions.py

@@ -2287,6 +2287,83 @@ class ARegionDroppedExtraBlocksNothing(unittest.TestCase):
             self.assertEqual(report({"foo.rom"}), {})
 
 
+class AnotherEmulatorsTreeProvesNothing(unittest.TestCase):
+    """lrps2 names no hash for pcsx2/resources/GameIndex.yaml; the only
+    full-tail copy was ARMSX2's, which counted as path proof and replaced
+    the GameIndex RetroArch pins on desktop targets, where ARMSX2 does not
+    exist. Upstream PCSX2 took ARMSX2's patches.zip by name the same way."""
+
+    def _db(self, root, files):
+        import hashlib
+
+        db = {"files": {}, "indexes": {"by_name": {}, "by_md5": {}, "by_crc32": {},
+                                       "by_path_suffix": {}}}
+        for relative, payload in files.items():
+            path = root / relative
+            path.parent.mkdir(parents=True, exist_ok=True)
+            path.write_bytes(payload)
+            sha1 = hashlib.sha1(payload).hexdigest()
+            db["files"][sha1] = {"path": relative, "name": path.name, "sha1": sha1,
+                                 "size": len(payload)}
+            db["indexes"]["by_name"].setdefault(path.name, []).append(sha1)
+            parts = relative.split("/")
+            for start in range(1, len(parts) - 1):
+                db["indexes"]["by_path_suffix"].setdefault(
+                    "/".join(parts[start:]), []).append(sha1)
+        return db
+
+    def test_neither_the_full_tail_nor_the_name_lands_in_a_foreign_tree(self):
+        from scripts.common import resolve_local_file
+
+        with tempfile.TemporaryDirectory(dir=TMP_ROOT) as directory:
+            root = Path(directory)
+            # The collection's layout, read relative to its root.
+            previous = os.getcwd()
+            os.chdir(root)
+            self.addCleanup(os.chdir, previous)
+            db = self._db(root, {
+                "bios/Other/armsx2/pcsx2/resources/GameIndex.yaml": b"fork",
+                "bios/Other/armsx2/pcsx2/resources/patches.zip": b"fork patches",
+                "bios/Sony/PlayStation 2/patches.zip": b"upstream patches",
+            })
+            index, status = resolve_local_file(
+                {"name": "GameIndex.yaml", "path": "pcsx2/resources/GameIndex.yaml",
+                 "source_profile": "lrps2"},
+                db, dest_hint="pcsx2/resources/GameIndex.yaml",
+            )
+            # Held only in the fork's tree, the file answers by name and
+            # proves nothing about this entry.
+            self.assertEqual(status, "name_exact")
+            patches, _status = resolve_local_file(
+                {"name": "patches.zip", "path": "resources/patches.zip",
+                 "source_profile": "pcsx2"},
+                db, dest_hint="resources/patches.zip",
+            )
+            self.assertTrue(patches.endswith("PlayStation 2/patches.zip"))
+
+    def test_no_desktop_retroarch_pack_serves_armsx2s_tree(self):
+        from scripts import slots
+        from scripts.common import (
+            load_data_dir_registry,
+            load_database,
+            load_emulator_profiles,
+            load_platform_config,
+            load_target_config,
+        )
+
+        if not (ROOT / "database.json").exists():
+            self.skipTest("database.json is not generated")
+        db = load_database(str(ROOT / "database.json"))
+        config = load_platform_config("retroarch", str(ROOT / "platforms"))
+        profiles = load_emulator_profiles(str(ROOT / "emulators"))
+        cores = set(load_target_config("retroarch", "x86_64", str(ROOT / "platforms")))
+        overrides = slots.pack_overrides(
+            config, profiles, db, None, load_data_dir_registry(str(ROOT / "platforms")),
+            target_cores=cores,
+        )
+        self.assertFalse([d for d, p in overrides.items() if "/armsx2/" in p])
+
+
 class TheDatabaseCacheIsWrittenWhole(unittest.TestCase):
     """A crash while serializing left a truncated db_cache.json behind, and
     the next run rehashed the whole collection from scratch."""