lib: add xor

This gets clumsily reimplemented in various places, to no useful end.

lib/default.nix

@@ -69,7 +69,7 @@ let
       hasAttr head isAttrs isBool isInt isList isPath isString length
       lessThan listToAttrs pathExists readFile replaceStrings seq
       stringLength sub substring tail trace;
-    inherit (self.trivial) id const pipe concat or and bitAnd bitOr bitXor
+    inherit (self.trivial) id const pipe concat or and xor bitAnd bitOr bitXor
       bitNot boolToString mergeAttrs flip mapNullable inNixShell isFloat min max
       importJSON importTOML warn warnIf warnIfNot throwIf throwIfNot checkListOfEnum
       info showWarnings nixpkgsVersion version isInOldestRelease

lib/tests/misc.nix

@@ -102,6 +102,7 @@ let
     types
     updateManyAttrsByPath
     versions
+    xor
     ;
 
   testingThrow = expr: {
@@ -210,6 +211,21 @@ runTests {
     expected = false;
   };
 
+  testXor = {
+    expr = [
+      (xor true false)
+      (xor true true)
+      (xor false false)
+      (xor false true)
+    ];
+    expected = [
+      true
+      false
+      false
+      true
+    ];
+  };
+
   testFix = {
     expr = fix (x: {a = if x ? a then "a" else "b";});
     expected = {a = "a";};

lib/trivial.nix

@@ -199,6 +199,24 @@ in {
   */
   and = x: y: x && y;
 
+  /**
+    boolean “exclusive or”
+
+
+    # Inputs
+
+    `x`
+
+    : 1\. Function argument
+
+    `y`
+
+    : 2\. Function argument
+  */
+  # We explicitly invert the arguments purely as a type assertion.
+  # This is invariant under XOR, so it does not affect the result.
+  xor = x: y: (!x) != (!y);
+
   /**
     bitwise “not”
   */

nixos/modules/config/users-groups.nix

@@ -871,7 +871,6 @@ in {
           }
           {
             assertion = let
-              xor = a: b: a && !b || b && !a;
               isEffectivelySystemUser = user.isSystemUser || (user.uid != null && user.uid < 1000);
             in xor isEffectivelySystemUser user.isNormalUser;
             message = ''

nixos/modules/services/networking/kea.nix

@@ -9,7 +9,6 @@ with lib;
 let
   cfg = config.services.kea;
 
-  xor = x: y: (!x && y) || (x && !y);
   format = pkgs.formats.json {};
 
   chooseNotNull = x: y: if x != null then x else y;

pkgs/development/compilers/llvm/13/default.nix

@@ -42,12 +42,9 @@
 
 }:
 
-assert let
+assert
-  int = a: if a then 1 else 0;
-  xor = a: b: ((builtins.bitXor (int a) (int b)) == 1);
-in
   lib.assertMsg
-    (xor
+    (lib.xor
       (gitRelease != null)
       (officialRelease != null))
     ("must specify `gitRelease` or `officialRelease`" +

pkgs/development/compilers/llvm/14/default.nix

@@ -41,12 +41,9 @@
 , monorepoSrc ? null
 }:
 
-assert let
+assert
-  int = a: if a then 1 else 0;
-  xor = a: b: ((builtins.bitXor (int a) (int b)) == 1);
-in
   lib.assertMsg
-    (xor
+    (lib.xor
       (gitRelease != null)
       (officialRelease != null))
     ("must specify `gitRelease` or `officialRelease`" +

pkgs/development/compilers/llvm/15/default.nix

@@ -41,12 +41,9 @@
 , monorepoSrc ? null
 }:
 
-assert let
+assert
-  int = a: if a then 1 else 0;
-  xor = a: b: ((builtins.bitXor (int a) (int b)) == 1);
-in
   lib.assertMsg
-    (xor
+    (lib.xor
       (gitRelease != null)
       (officialRelease != null))
     ("must specify `gitRelease` or `officialRelease`" +

pkgs/development/compilers/llvm/16/default.nix

@@ -41,12 +41,9 @@
 , monorepoSrc ? null
 }:
 
-assert let
+assert
-  int = a: if a then 1 else 0;
-  xor = a: b: ((builtins.bitXor (int a) (int b)) == 1);
-in
   lib.assertMsg
-    (xor
+    (lib.xor
       (gitRelease != null)
       (officialRelease != null))
     ("must specify `gitRelease` or `officialRelease`" +

pkgs/development/compilers/llvm/17/default.nix

@@ -41,12 +41,9 @@
 , monorepoSrc ? null
 }:
 
-assert let
+assert
-  int = a: if a then 1 else 0;
-  xor = a: b: ((builtins.bitXor (int a) (int b)) == 1);
-in
   lib.assertMsg
-    (xor
+    (lib.xor
       (gitRelease != null)
       (officialRelease != null))
     ("must specify `gitRelease` or `officialRelease`" +

pkgs/development/compilers/llvm/18/default.nix

@@ -41,12 +41,9 @@
 , monorepoSrc ? null
 }:
 
-assert let
+assert
-  int = a: if a then 1 else 0;
-  xor = a: b: ((builtins.bitXor (int a) (int b)) == 1);
-in
   lib.assertMsg
-    (xor
+    (lib.xor
       (gitRelease != null)
       (officialRelease != null))
     ("must specify `gitRelease` or `officialRelease`" +

pkgs/development/compilers/llvm/git/default.nix

@@ -46,12 +46,9 @@
 , monorepoSrc ? null
 }:
 
-assert let
+assert
-  int = a: if a then 1 else 0;
-  xor = a: b: ((builtins.bitXor (int a) (int b)) == 1);
-in
   lib.assertMsg
-    (xor
+    (lib.xor
       (gitRelease != null)
       (officialRelease != null))
     ("must specify `gitRelease` or `officialRelease`" +