prevent cyclical dependency detection false positives

src/compile/Component.ts

@@ -857,12 +857,14 @@ export default class Component {
 			declaration.dependencies.forEach(name => {
 				if (declaration.assignees.has(name)) return;
 				const earlier_declarations = lookup.get(name);
-				if (earlier_declarations) earlier_declarations.forEach(add_declaration);
+				if (earlier_declarations) earlier_declarations.forEach(declaration => {
+					if (this.reactive_declarations.indexOf(declaration) === -1) {
+						add_declaration(declaration);
+					}
+				});
 			});
 
-			if (this.reactive_declarations.indexOf(declaration) === -1) {
 			this.reactive_declarations.push(declaration);
-			}
 		};
 
 		unsorted_reactive_declarations.forEach(declaration => {

test/runtime/samples/reactive-values-second-order/_config.js

@@ -0,0 +1,8 @@
+export default {
+	test({ assert, component, target }) {
+		assert.equal(component.qux, 2);
+
+		component.foo = 2;
+		assert.equal(component.qux, 4);
+	}
+};

test/runtime/samples/reactive-values-second-order/main.html

@@ -0,0 +1,12 @@
+<script>
+	export let foo = 1, bar, baz, qux;
+
+	$: {
+		bar = foo;
+		baz = foo;
+	}
+
+	$: {
+		qux = bar + baz;
+	}
+</script>