" outPath = builtins.storePath " . $inputInfo->{$argName}->{storePath} . ";" .

        my $pkgNameRE = "(?:(?:[A-Za-z0-9]|(?:-[^0-9]))+)";
        my $versionRE = "(?:[A-Za-z0-9\.\-]+)";

        my $relName = ($prevBuild->resultInfo->releasename or $prevBuild->nixname);
        my $version = $2 if $relName =~ /^($pkgNameRE)-($versionRE)$/;

        push @newArgs, "--arg", $argName, "{path = builtins.storePath " . $prevBuild->outpath . ";}";

        push @newArgs, "--arg", $argName,
            "{ path = builtins.storePath " . $prevBuild->outpath . "; " .
            "  outPath = builtins.storePath " . $prevBuild->outpath . "; " .
            ($version ? "  version = \"$version\"; " : "") . # !!! escape
            "}";