make-derivation: allow nested lists in buildInputs

This isn't really desirable in general, but given that Nix itself
currently relies on this behaviour and that we don't want to break
backwards compatibility we should support it for now, maybe
deprecating it in the future.

pkgs/stdenv/generic/make-derivation.nix

@@ -129,9 +129,11 @@ let
   # hardeningDisable additionally supports "all".
   erroneousHardeningFlags = lib.subtractLists supportedHardeningFlags (hardeningEnable ++ lib.remove "all" hardeningDisable);
 
-  checkDependencyList = name: deps: lib.flip lib.imap1 deps (index: dep:
+  checkDependencyList = checkDependencyList' [];
+  checkDependencyList' = positions: name: deps: lib.flip lib.imap1 deps (index: dep:
     if lib.isDerivation dep || isNull dep || builtins.typeOf dep == "path" then dep
-    else throw "Dependency is not of a valid type: element ${toString index} of ${name} for ${attrs.name or attrs.pname}");
+    else if lib.isList dep then checkDependencyList' ([index] ++ positions) name dep
+    else throw "Dependency is not of a valid type: ${lib.concatMapStrings (ix: "element ${toString ix} of ") ([index] ++ positions)}${name} for ${attrs.name or attrs.pname}");
 in if builtins.length erroneousHardeningFlags != 0
 then abort ("mkDerivation was called with unsupported hardening flags: " + lib.generators.toPretty {} {
   inherit erroneousHardeningFlags hardeningDisable hardeningEnable supportedHardeningFlags;