refactor: index records by path in slots

scripts/slots.py

@@ -746,11 +746,26 @@ def _declared_hashes(entry: dict, field_name: str) -> set[str]:
     }
 
 
+def _record_at(path: str, db: dict) -> dict | None:
+    """The database record stored at path, from an index built once per db.
+
+    A scan of db['files'] on every call was O(calls x 19 000 files) on the
+    path verify --all and slots.py both take.
+    """
+    files = db.get("files", {})
+    cached = _PATH_INDEX.get(id(files))
+    if cached is None or cached[0] is not files:
+        cached = (files, {e.get("path"): e for e in files.values()})
+        _PATH_INDEX[id(files)] = cached
+    return cached[1].get(path)
+
+
+_PATH_INDEX: dict[int, tuple[dict, dict[str, dict]]] = {}
+
+
 def _accepted_by_all(path: str, entries: list[dict], db: dict) -> bool:
     """Whether every declaration's own hashes accept the file at path."""
-    record = next(
-        (e for e in db.get("files", {}).values() if e.get("path") == path), None
-    )
+    record = _record_at(path, db)
     if record is None:
         return False
     for entry in entries:

tests/test_slots.py

@@ -834,5 +834,26 @@ class SlotsJudgeWhatVerifyJudged(unittest.TestCase):
         self.assertIn("--include-archived", result.stderr)
 
 
+class ARecordIsFoundByItsPathOnce(unittest.TestCase):
+    """_accepted_by_all walked all 19 000 records for every path asked."""
+
+    def test_the_files_are_walked_once(self):
+        import slots  # noqa: PLC0415
+
+        class Counted(dict):
+            walks = 0
+
+            def values(self):
+                Counted.walks += 1
+                return super().values()
+
+        files = Counted({"a" * 40: {"path": "bios/x.bin"}, "b" * 40: {"path": "bios/y.bin"}})
+        db = {"files": files}
+        for _ in range(50):
+            self.assertEqual(slots._record_at("bios/y.bin", db)["path"], "bios/y.bin")
+        self.assertIsNone(slots._record_at("bios/z.bin", db))
+        self.assertEqual(Counted.walks, 1)
+
+
 if __name__ == "__main__":
     unittest.main()