Fixes shorthand class directives which do not have classes

Fixes #1739

src/compile/nodes/Element.ts

@@ -1326,7 +1326,7 @@ export default class Element extends Node {
 				dependencies = expression.dependencies;
 			} else {
 				snippet = `ctx${quotePropIfNecessary(name)}`;
-				dependencies = [name];
+				dependencies = new Set([name]);
 			}
 			const updater = `@toggleClass(${this.var}, "${name}", ${snippet});`;
 

test/runtime/samples/class-shortcut-with-class/_config.js

@@ -0,0 +1,16 @@
+export default {
+	data: {
+		"is-active": true,
+		isSelected: true,
+		myClass: 'one two'
+	},
+	html: `<div class="one two is-active isSelected"></div>`,
+
+	test ( assert, component, target, window ) {
+		component.set({ "is-active": false });
+
+		assert.htmlEqual( target.innerHTML, `
+			<div class="one two isSelected"></div>
+		` );
+	}
+};

test/runtime/samples/class-shortcut-with-class/main.html

@@ -0,0 +1 @@
+<div class="{ myClass }" class:is-active class:isSelected class:not-used></div>

test/runtime/samples/class-shortcut/_config.js

@@ -1,16 +1,15 @@
 export default {
 	data: {
 		"is-active": true,
-		isSelected: true,
+		isSelected: true
-		myClass: 'one two'
 	},
-	html: `<div class="one two is-active isSelected"></div>`,
+	html: `<div class="is-active isSelected"></div>`,
 
 	test ( assert, component, target, window ) {
 		component.set({ "is-active": false });
 
 		assert.htmlEqual( target.innerHTML, `
-			<div class="one two isSelected"></div>
+			<div class="isSelected"></div>
 		` );
 	}
 };

test/runtime/samples/class-shortcut/main.html

@@ -1 +1 @@
-<div class="{ myClass }" class:is-active class:isSelected class:not-used></div>
+<div class:is-active class:isSelected class:not-used></div>