lib: add importTOML

Complements the `lib.importJSON`. `builtins.readTOML` has been
introduced in Nix 2.1.

lib/default.nix

@@ -66,7 +66,7 @@ let
       stringLength sub substring tail;
     inherit (trivial) id const pipe concat or and bitAnd bitOr bitXor
       bitNot boolToString mergeAttrs flip mapNullable inNixShell min max
-      importJSON warn info showWarnings nixpkgsVersion version mod compare
+      importJSON importTOML warn info showWarnings nixpkgsVersion version mod compare
       splitByAndCompare functionArgs setFunctionArgs isFunction toHexString toBaseDigits;
     inherit (fixedPoints) fix fix' converge extends composeExtensions
       makeExtensible makeExtensibleWithCustomName;

lib/trivial.nix

@@ -281,6 +281,12 @@ rec {
   importJSON = path:
     builtins.fromJSON (builtins.readFile path);
 
+  /* Reads a TOML file.
+
+     Type :: path -> any
+  */
+  importTOML = path:
+    builtins.fromTOML (builtins.readFile path);
 
   ## Warnings