From 8e8b3fa1bb3aaabae1cf7fabd6e91e4f4300cb6d Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Wed, 29 Sep 2021 14:34:24 +0200
Subject: [PATCH] invalidateFetcherByDrvHash: Add self-check

... so it won't break when the fetcher doesn't use name correctly.
---
 pkgs/top-level/all-packages.nix | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 2865279cbddb..d28ff9fdb813 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -618,7 +618,15 @@ with pkgs;
       drvPath = (f args).drvPath;
       # It's safe to discard the context, because we don't access the path.
       salt = builtins.unsafeDiscardStringContext (lib.substring 0 12 (baseNameOf drvPath));
-    in f (args // { name = "${args.name or "source"}-salted-${salt}"; });
+      # New derivation incorporating the original drv hash in the name
+      salted = f (args // { name = "${args.name or "source"}-salted-${salt}"; });
+      # Make sure we did change the derivation. If the fetcher ignores `name`,
+      # `invalidateFetcherByDrvHash` doesn't work.
+      checked =
+        if salted.drvPath == drvPath
+        then throw "invalidateFetcherByDrvHash: Adding the derivation hash to the fixed-output derivation name had no effect. Make sure the fetcher's name argument ends up in the derivation name. Otherwise, the fetcher will not be re-run when its implementation changes. This is important for testing."
+        else salted;
+    in checked;
 
   lazydocker = callPackage ../tools/misc/lazydocker { };