lib/modules: Test the ability for config to depend on options for compatibility

lib/tests/modules.sh

@@ -185,6 +185,11 @@ checkConfigError 'The option .* defined in .* does not exist' config.enable ./di
 # Check that imports can depend on derivations
 checkConfigOutput "true" config.enable ./import-from-store.nix
 
+# Check that configs can be conditional on option existence
+checkConfigOutput true config.enable ./define-option-dependently.nix ./declare-enable.nix ./declare-int-positive-value.nix
+checkConfigOutput 360 config.value ./define-option-dependently.nix ./declare-enable.nix ./declare-int-positive-value.nix
+checkConfigOutput 7 config.value ./define-option-dependently.nix ./declare-int-positive-value.nix
+
 # Check attrsOf and lazyAttrsOf. Only lazyAttrsOf should be lazy, and only
 # attrsOf should work with conditional definitions
 # In addition, lazyAttrsOf should honor an options emptyValue

lib/tests/modules/define-option-dependently.nix

@@ -0,0 +1,16 @@
+{ lib, options, ... }:
+
+# Some modules may be distributed separately and need to adapt to other modules
+# that are distributed and versioned separately.
+{
+
+  # Always defined, but the value depends on the presence of an option.
+  config = {
+    value = if options ? enable then 360 else 7;
+  } 
+  # Only define if possible.
+  // lib.optionalAttrs (options ? enable) {
+    enable = true;
+  };
+
+}