lib: Add optionalDrvAttr to conditionally set drv attributes.

This allows for adding new, conditionally set, derivation attributes
to an existing derivation without changing any output paths in the
case where the condition is not met.

1 files changed, 19 insertions, 1 deletions

diff --git a/lib/tests/misc.nix b/lib/tests/misc.nix
index 3059878ba0695..193e68a96933c 100644
--- a/lib/tests/misc.nix
+++ b/lib/tests/misc.nix
@@ -1902,7 +1902,7 @@ runTests {
     expected = true;
   };
 
-  # lazyDerivation
+  # DERIVATIONS
 
   testLazyDerivationIsLazyInDerivationForAttrNames = {
     expr = attrNames (lazyDerivation {
@@ -1955,6 +1955,24 @@ runTests {
     expected = derivation;
   };
 
+  testOptionalDrvAttr = let
+    mkDerivation = args: derivation (args // {
+      builder = "builder";
+      system = "system";
+      __ignoreNulls = true;
+    });
+  in {
+    expr = (mkDerivation {
+      name = "foo";
+      x = optionalDrvAttr true 1;
+      y = optionalDrvAttr false 1;
+    }).drvPath;
+    expected = (mkDerivation {
+      name = "foo";
+      x = 1;
+    }).drvPath;
+  };
+
   testTypeDescriptionInt = {
     expr = (with types; int).description;
     expected = "signed integer";