Use theme API for add/remove "icon" theme variant (#95) (#96)

Fixes #93

src/main/java/com/vaadin/flow/component/button/Button.java

@@ -374,7 +374,7 @@ public boolean isAutofocus() {
      * Enabling the button needs to happen from the server.
      *
      * @param disableOnClick
-     *         true to disable button immediately when clicked
+     *            true to disable button immediately when clicked
      */
     public void setDisableOnClick(boolean disableOnClick) {
         this.disableOnClick = disableOnClick;
@@ -453,16 +453,14 @@ private Element[] getTextNodes() {
     }
 
     private void updateThemeAttribute() {
-        // Set attribute theme="icon" when the button contains only an icon to
+        // Add theme attribute "icon" when the button contains only an icon to
         // fully support themes like Valo. This doesn't override explicitly set
         // theme attribute.
-        String theme = getElement().getAttribute(THEME_ATTRIBUTE);
 
-        if (theme == null && getElement().getChildCount() == 1
-                && iconComponent != null) {
-            getElement().setAttribute(THEME_ATTRIBUTE, "icon");
-        } else if ("icon".equals(theme)) {
-            getElement().removeAttribute(THEME_ATTRIBUTE);
+        if (getElement().getChildCount() == 1 && iconComponent != null) {
+            getThemeNames().add("icon");
+        } else {
+            getThemeNames().remove("icon");
         }
     }
 }

src/main/java/com/vaadin/flow/component/button/ButtonVariant.java

@@ -1,12 +1,12 @@
 /*
  * Copyright 2000-2018 Vaadin Ltd.
- * 
+ *
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not
  * use this file except in compliance with the License. You may obtain a copy of
  * the License at
- * 
+ *
  * http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
@@ -20,8 +20,8 @@
 /**
  * Set of theme variants applicable for {@code vaadin-button} component.
  */
-@Generated({ "Generator: com.vaadin.generator.ComponentGenerator#1.1-SNAPSHOT",
-        "WebComponent: Vaadin.ButtonElement#2.1.0", "Flow#1.1-SNAPSHOT" })
+@Generated({ "Generator: com.vaadin.generator.ComponentGenerator#1.2-SNAPSHOT",
+        "WebComponent: Vaadin.ButtonElement#2.1.0", "Flow#1.2-SNAPSHOT" })
 public enum ButtonVariant {
     LUMO_SMALL("small"), LUMO_LARGE("large"), LUMO_TERTIARY(
             "tertiary"), LUMO_TERTIARY_INLINE("tertiary-inline"), LUMO_PRIMARY(
@@ -39,7 +39,7 @@ public enum ButtonVariant {
 
     /**
      * Gets the variant name.
-     * 
+     *
      * @return variant name
      */
     public String getVariantName() {

src/test/java/com/vaadin/flow/component/button/tests/ButtonTest.java

@@ -15,13 +15,15 @@
  */
 package com.vaadin.flow.component.button.tests;
 
+import java.util.Set;
 import java.util.function.Predicate;
 
 import org.junit.Assert;
 import org.junit.Test;
 
 import com.vaadin.flow.component.Text;
 import com.vaadin.flow.component.button.Button;
+import com.vaadin.flow.component.button.ButtonVariant;
 import com.vaadin.flow.component.icon.Icon;
 import com.vaadin.flow.component.icon.VaadinIcon;
 import com.vaadin.flow.dom.Element;
@@ -139,19 +141,19 @@ public void changeOrder_setIcon_setText_changeOrder() {
     @Test
     public void updatingThemeAttribute() {
         button = new Button();
-        assertButtonHasThemeAttribute(null);
+        assertButtonHasNoThemeAttribute();
 
         button.setIcon(new Icon());
         assertButtonHasThemeAttribute(THEME_ATTRIBUTE_ICON);
 
         button.setText("foo");
-        assertButtonHasThemeAttribute(null);
+        assertButtonHasNoThemeAttribute();
 
         button.setIcon(null);
-        assertButtonHasThemeAttribute(null);
+        assertButtonHasNoThemeAttribute();
 
         button = new Button("foo", new Icon());
-        assertButtonHasThemeAttribute(null);
+        assertButtonHasNoThemeAttribute();
 
         button.setText("");
         assertButtonHasThemeAttribute(THEME_ATTRIBUTE_ICON);
@@ -223,6 +225,42 @@ public void setText_slotAttributeIsPreserved() {
         Assert.assertEquals("prefix", icon.getElement().getAttribute("slot"));
     }
 
+    @Test
+    public void addThemeVariant_setIcon_themeAttributeContiansThemeVariantAndIcon() {
+        button = new Button();
+        button.addThemeVariants(ButtonVariant.LUMO_SUCCESS);
+        button.setIcon(new Icon(VaadinIcon.ARROW_RIGHT));
+
+        Set<String> themeNames = button.getThemeNames();
+        Assert.assertTrue(themeNames.contains("icon"));
+        Assert.assertTrue(themeNames
+                .contains(ButtonVariant.LUMO_SUCCESS.getVariantName()));
+    }
+
+    @Test
+    public void setIcon_addThemeVariant_themeAttributeContiansThemeVariantAndIcon() {
+        button = new Button();
+        button.setIcon(new Icon(VaadinIcon.ARROW_RIGHT));
+        button.addThemeVariants(ButtonVariant.LUMO_SUCCESS);
+
+        Set<String> themeNames = button.getThemeNames();
+        Assert.assertTrue(themeNames.contains("icon"));
+        Assert.assertTrue(themeNames
+                .contains(ButtonVariant.LUMO_SUCCESS.getVariantName()));
+    }
+
+    @Test
+    public void changeIcon_iconThemeIsPreserved() {
+        button = new Button();
+        button.setIcon(new Icon(VaadinIcon.ARROW_RIGHT));
+
+        Assert.assertEquals("icon", button.getThemeName());
+
+        button.setIcon(new Icon(VaadinIcon.ALARM));
+
+        Assert.assertEquals("icon", button.getThemeName());
+    }
+
     private void assertOnlyChildIsText() {
         Assert.assertEquals(1, button.getElement().getChildCount());
         Element child = getButtonChild(0);
@@ -248,13 +286,12 @@ private void assertIconAndSpan(boolean iconAfterText) {
     }
 
     private void assertButtonHasThemeAttribute(String theme) {
-        if (theme == null) {
-            Assert.assertFalse(
-                    button.getElement().hasAttribute(THEME_ATTRIBUTE));
-        } else {
-            Assert.assertEquals(theme,
-                    button.getElement().getAttribute(THEME_ATTRIBUTE));
-        }
+        Assert.assertTrue("Expected " + theme + " to be in the theme attribute",
+                button.getThemeNames().contains(theme));
+    }
+
+    private void assertButtonHasNoThemeAttribute() {
+        Assert.assertNull(button.getElement().getAttribute("theme"));
     }
 
     private void assertIconBeforeText() {