Merge pull request #301556 from edef1c/lib-xor

lib: add xor

3 files changed, 35 insertions, 1 deletions

diff --git a/lib/default.nix b/lib/default.nix
index f6cb7932507a..b442ddf5fa0f 100644
--- a/lib/default.nix
+++ b/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
diff --git a/lib/tests/misc.nix b/lib/tests/misc.nix
index da5e32297509..accceb4ddf9c 100644
--- a/lib/tests/misc.nix
+++ b/lib/tests/misc.nix
@@ -106,6 +106,7 @@ let
     types
     updateManyAttrsByPath
     versions
+    xor
     ;
 
   testingThrow = expr: {
@@ -214,6 +215,21 @@ 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";};
diff --git a/lib/trivial.nix b/lib/trivial.nix
index 936ad207c03d..5b7a1ee30f7a 100644
--- a/lib/trivial.nix
+++ b/lib/trivial.nix
@@ -200,6 +200,24 @@ 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”
   */
   bitNot = builtins.sub (-1);