Implement object merge operator

src/transformers/attribute-sets.js

@@ -166,6 +166,7 @@ module.exports = {
 				let hasOverrides = bindings.some((binding) => binding.name === "__overrides");
 
 				if (isRecursive) {
+					// __overrides is only respected in recursive attribute sets, in the upstream implementation
 					if (hasOverrides) {
 						throw new Error(`The __overrides feature is not supported in jsNix`);
 					}

src/transformers/index.js

@@ -75,6 +75,11 @@ let trivial = {
 				// FIXME: Need to replace this with utility functions to deal with eg. paths
 				if (node.operator === "&&" || node.operator === "||") {
 					return types.logicalExpression(node.operator, node.left, node.right);
+				} if (node.operator === "//") {
+					return types.objectExpression([
+						types.spreadElement(node.left),
+						types.spreadElement(node.right)
+					]);
 				} else {
 					return types.binaryExpression(node.operator, node.left, node.right);
 				}