pkgs.testers.invalidateFetcherByDrvHash

The following is the current implementation of this function.

invalidateFetcherByDrvHash = f: args:
    let
      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));
      # 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;