Revert "Add isPath to trivial.nix"

This breaks NixOS, and I don't actually need it, so someone who needs it
can bring this back without breaking NixOS :)

This reverts commit 2742087bdd.

Signed-off-by: Shea Levy <shea@shealevy.com>

pkgs/lib/modules.nix

@@ -11,6 +11,17 @@ with import ./options.nix;
 with import ./properties.nix;
 
 rec {
+
+  # Unfortunately this can also be a string.
+  isPath = x: !(
+     builtins.isFunction x
+  || builtins.isAttrs x
+  || builtins.isInt x
+  || builtins.isBool x
+  || builtins.isList x
+  );
+
+
   importIfPath = path:
     if isPath path then
       import path

pkgs/lib/trivial.nix

@@ -35,14 +35,4 @@ rec {
     else if builtins.isAttrs x
       then deepSeqAttrs x y
       else seq x y;
-
-  isPath = val: with builtins; !(
-      isAttrs val
-   || isList val
-   || isInt val
-   || isString val
-   || isFunction val
-   || isBool val
-   || val == null
-  );
 }

pkgs/lib/types.nix

@@ -96,7 +96,8 @@ rec {
 
     path = mkOptionType {
       name = "path";
-      check = lib.traceValIfNot isPath;
+      # Hacky: there is no ‘isPath’ primop.
+      check = lib.traceValIfNot (x: builtins.unsafeDiscardStringContext (builtins.substring 0 1 (toString x)) == "/");
     };
 
     listOf = types.list;