treewide: use lib.optional instead of 'then []'

nixos/lib/eval-config.nix

@@ -31,7 +31,7 @@ evalConfigArgs@
 , prefix ? []
 , lib ? import ../../lib
 , extraModules ? let e = builtins.getEnv "NIXOS_EXTRA_MODULE_PATH";
-                 in if e == "" then [] else [(import e)]
+                 in lib.optional (e != "") (import e)
 }:
 
 let pkgs_ = pkgs;

nixos/modules/installer/netboot/netboot.nix

@@ -39,9 +39,7 @@ with lib;
 
     # !!! Hack - attributes expected by other modules.
     environment.systemPackages = [ pkgs.grub2_efi ]
-      ++ (if pkgs.stdenv.hostPlatform.system == "aarch64-linux"
-          then []
-          else [ pkgs.grub2 pkgs.syslinux ]);
+      ++ (lib.optionals (pkgs.stdenv.hostPlatform.system != "aarch64-linux") [pkgs.grub2 pkgs.syslinux]);
 
     fileSystems."/" = mkImageMediaOverride
       { fsType = "tmpfs";

nixos/modules/services/misc/zoneminder.nix

@@ -351,7 +351,7 @@ in {
           CacheDirectory = dirs cacheDirs;
           RuntimeDirectory = dirName;
           ReadWriteDirectories = lib.mkIf useCustomDir [ cfg.storageDir ];
-          StateDirectory = dirs (if useCustomDir then [] else libDirs);
+          StateDirectory = dirs (lib.optional (!useCustomDir) libDirs);
           LogsDirectory = dirName;
           PrivateTmp = true;
           ProtectSystem = "strict";

nixos/modules/services/search/kibana.nix

@@ -130,9 +130,9 @@ in {
 
           This defaults to the singleton list [ca] when the {option}`ca` option is defined.
         '';
-        default = if cfg.elasticsearch.ca == null then [] else [ca];
+        default = lib.optional (cfg.elasticsearch.ca != null) ca;
         defaultText = literalExpression ''
-          if config.${opt.elasticsearch.ca} == null then [ ] else [ ca ]
+          lib.optional (config.${opt.elasticsearch.ca} != null) ca
         '';
         type = types.listOf types.path;
       };

nixos/modules/services/security/kanidm.nix

@@ -17,7 +17,7 @@ let
       # If the new path is a prefix to some existing path, we need to filter it out
       filteredPaths = lib.filter (p: !lib.hasPrefix (builtins.toString newPath) (builtins.toString p)) merged;
       # If a prefix of the new path is already in the list, do not add it
-      filteredNew = if hasPrefixInList filteredPaths newPath then [] else [ newPath ];
+      filteredNew = lib.optional (!hasPrefixInList filteredPaths newPath) newPath;
     in filteredPaths ++ filteredNew) [];
 
   defaultServiceConfig = {

nixos/modules/services/web-apps/restya-board.nix

@@ -263,8 +263,8 @@ in
       serviceConfig.RemainAfterExit = true;
 
       wantedBy = [ "multi-user.target" ];
-      requires = if cfg.database.host == null then [] else [ "postgresql.service" ];
-      after = [ "network.target" ] ++ (if cfg.database.host == null then [] else [ "postgresql.service" ]);
+      requires = lib.optional (cfg.database.host != null) "postgresql.service";
+      after = [ "network.target" ] ++ (lib.optional (cfg.database.host != null) "postgresql.service");
 
       script = ''
         rm -rf "${runDir}"

nixos/tests/common/resolver.nix

@@ -63,7 +63,7 @@
             matched = builtins.match "[ \t]+(${reHost})(.*)" str;
             continue = lib.singleton (lib.head matched)
                     ++ matchAliases (lib.last matched);
-          in if matched == null then [] else continue;
+          in lib.optional (matched != null) continue;
 
           matchLine = str: let
             result = builtins.match "[ \t]*(${reIp})[ \t]+(${reHost})(.*)" str;

pkgs/build-support/nix-gitignore/default.nix

@@ -45,7 +45,7 @@ in rec {
           escs = "\\*?";
           splitString =
             let recurse = str : [(substring 0 1 str)] ++
-                                 (if str == "" then [] else (recurse (substring 1 (stringLength(str)) str) ));
+                                 (lib.optionals (str != "") (recurse (substring 1 (stringLength(str)) str) ));
             in str : recurse str;
           chars = s: filter (c: c != "" && !isList c) (splitString s);
           escape = s: map (c: "\\" + c) (chars s);

pkgs/development/coq-modules/mathcomp-analysis/default.nix

@@ -40,8 +40,7 @@ let
   mathcomp_ = package: let
       classical-deps = [ mathcomp.algebra mathcomp-finmap ];
       analysis-deps = [ mathcomp.field mathcomp-bigenough ];
-      intra-deps = if package == "single" then []
-        else map mathcomp_ (head (splitList (lib.pred.equal package) packages));
+      intra-deps = lib.optionals (package != "single") (map mathcomp_ (head (splitList (lib.pred.equal package) packages)));
       pkgpath = if package == "single" then "."
         else if package == "analysis" then "theories" else "${package}";
       pname = if package == "single" then "mathcomp-analysis-single"

pkgs/development/coq-modules/mathcomp/default.nix

@@ -55,8 +55,7 @@ let
   packages = [ "ssreflect" "fingroup" "algebra" "solvable" "field" "character" "all" ];
 
   mathcomp_ = package: let
-      mathcomp-deps = if package == "single" then []
-        else map mathcomp_ (head (splitList (lib.pred.equal package) packages));
+      mathcomp-deps = lib.optionals (package != "single") (map mathcomp_ (head (splitList (lib.pred.equal package) packages)));
       pkgpath = if package == "single" then "mathcomp" else "mathcomp/${package}";
       pname = if package == "single" then "mathcomp" else "mathcomp-${package}";
       pkgallMake = ''

pkgs/development/coq-modules/metacoq/default.nix

@@ -33,8 +33,7 @@ let
   template-coq = metacoq_ "template-coq";
 
   metacoq_ = package: let
-      metacoq-deps = if package == "single" then []
-        else map metacoq_ (head (splitList (lib.pred.equal package) packages));
+      metacoq-deps = lib.optionals (package != "single") (map metacoq_ (head (splitList (lib.pred.equal package) packages)));
       pkgpath = if package == "single" then "./" else "./${package}";
       pname = if package == "all" then "metacoq" else "metacoq-${package}";
       pkgallMake = ''

pkgs/development/libraries/protobuf/generic-v3.nix

@@ -33,7 +33,7 @@ mkProtobufDerivation = buildProtobuf: stdenv: stdenv.mkDerivation {
   nativeBuildInputs = [ autoreconfHook buildPackages.which buildPackages.stdenv.cc buildProtobuf ];
 
   buildInputs = [ zlib ];
-  configureFlags = if buildProtobuf == null then [] else [ "--with-protoc=${buildProtobuf}/bin/protoc" ];
+  configureFlags = lib.optional (buildProtobuf != null) "--with-protoc=${buildProtobuf}/bin/protoc";
 
   enableParallelBuilding = true;
 

pkgs/tools/system/netdata/default.nix

@@ -65,7 +65,7 @@ stdenv.mkDerivation rec {
   # to bootstrap tools:
   #   https://github.com/NixOS/nixpkgs/pull/175719
   # We pick zlib.dev as a simple canary package with pkg-config input.
-  disallowedReferences = if withDebug then [] else [ zlib.dev ];
+  disallowedReferences = lib.optional (!withDebug) zlib.dev;
 
   donStrip = withDebug;
   env.NIX_CFLAGS_COMPILE = lib.optionalString withDebug "-O1 -ggdb -DNETDATA_INTERNAL_CHECKS=1";