fbcode_builder: SystemPackageFetcher.hash() — hash package list, not bool

Summary: If `self.installed` is not a hash of what was installed then we handle it differently to take into account packages where we're relying on the system.

Reviewed By: bigfootjon

Differential Revision: D104428972

fbshipit-source-id: af51081007166de311b15f2b627d4cec77a91df4

Author: r-barnes

build/fbcode_builder/getdeps/fetcher.py

@@ -254,8 +254,16 @@ def update(self) -> ChangeStatus:
 
     def hash(self) -> str:
         if self.packages_are_installed():
-            # pyrefly: ignore [bad-argument-type]
-            return hashlib.sha256(self.installed).hexdigest()
+            # SystemPackageFetcher stashes the package-manager query output
+            # (bytes including versions) in self.installed so upgrades change
+            # the hash. PreinstalledNopFetcher just sets self.installed=True
+            # and has no .packages, so fall back to an empty package list.
+            if isinstance(self.installed, (bytes, bytearray)):
+                payload = bytes(self.installed)
+            else:
+                packages = getattr(self, "packages", None) or []
+                payload = ",".join(sorted(packages)).encode("utf-8")
+            return hashlib.sha256(payload).hexdigest()
         else:
             return "0" * 40