From 4fc67da841d1c80b8d774a7b8c8e6baf13f9496e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Romildo?= <malaquias@gmail.com>
Date: Sun, 9 Jan 2022 19:12:27 -0300
Subject: [PATCH] lib.checkListOfEnum: init

---
 lib/default.nix |  2 +-
 lib/trivial.nix | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/lib/default.nix b/lib/default.nix
index fe5d2db0db8f..2dfe62e82a8b 100644
--- a/lib/default.nix
+++ b/lib/default.nix
@@ -66,7 +66,7 @@ let
       stringLength sub substring tail trace;
     inherit (self.trivial) id const pipe concat or and bitAnd bitOr bitXor
       bitNot boolToString mergeAttrs flip mapNullable inNixShell isFloat min max
-      importJSON importTOML warn warnIf throwIfNot
+      importJSON importTOML warn warnIf throwIfNot checkListOfEnum
       info showWarnings nixpkgsVersion version
       mod compare splitByAndCompare functionArgs setFunctionArgs isFunction
       toHexString toBaseDigits;
diff --git a/lib/trivial.nix b/lib/trivial.nix
index c961d3aa7301..575aaf6a7ad4 100644
--- a/lib/trivial.nix
+++ b/lib/trivial.nix
@@ -347,6 +347,23 @@ rec {
   */
   throwIfNot = cond: msg: if cond then x: x else throw msg;
 
+  /* Check if the elements in a list are valid values from a enum, returning the identity function, or throwing an error message otherwise.
+
+     Example:
+       let colorVariants = ["bright" "dark" "black"]
+       in checkListOfEnum "color variants" [ "standard" "light" "dark" ] colorVariants;
+       =>
+       error: color variants: bright, black unexpected; valid ones: standard, light, dark
+
+     Type: String -> List ComparableVal -> List ComparableVal -> a -> a
+  */
+  checkListOfEnum = msg: valid: given:
+    let
+      unexpected = lib.subtractLists valid given;
+    in
+      lib.throwIfNot (unexpected == [])
+        "${msg}: ${builtins.concatStringsSep ", " (builtins.map builtins.toString unexpected)} unexpected; valid ones: ${builtins.concatStringsSep ", " (builtins.map builtins.toString valid)}";
+
   info = msg: builtins.trace "INFO: ${msg}";
 
   showWarnings = warnings: res: lib.foldr (w: x: warn w x) res warnings;