Add documentation for enum based selects

enums are an easy way to select from a fixed set of choices that don't
need configuration.

Author: mawinter69

src/main/java/io/jenkins/plugins/designlibrary/Select.java

@@ -34,6 +34,11 @@ public Fruit getFruit() {
         return null;
     }
 
+    private Unit unit;
+    public Unit getUnit() {
+        return unit;
+    }
+
     public DescriptorExtensionList<Fruit, Descriptor<Fruit>> getFruitDescriptors() {
         return Jenkins.get().getDescriptorList(Fruit.class);
     }
@@ -182,4 +187,22 @@ public static final class DescriptorImpl extends FruitDescriptor {}
         "Wisconsin",
         "Wyoming"
     };
+
+    public enum Unit {
+        MILLISECONDS("Milliseconds"),
+        SECONDS("Seconds"),
+        MINUTES("Minutes"),
+        HOURS("Hours"),
+        DAYS("Days");
+
+        private final String description;
+
+        Unit(String description) {
+            this.description = description;
+        }
+
+        public String getDescription() {
+            return description;
+        }
+    }
 }

src/main/resources/io/jenkins/plugins/designlibrary/Select/index.jelly

@@ -42,6 +42,26 @@ THE SOFTWARE.
       </s:group>
     </s:section>
 
+    <s:section title="${%Enum select}" description="${%usage.enum}">
+      <s:group>
+        <s:preview>
+          <f:entry title="Unit" field="unit">
+            <f:enum default="SECONDS">
+              ${it.description}
+            </f:enum>
+          </f:entry>
+        </s:preview>
+        <s:code-panes>
+          <s:code-pane title="Jelly">
+            <s:code file="enum.jelly"/>
+          </s:code-pane>
+          <s:code-pane title="Java">
+            <s:code language="java" file="Enum.java"/>
+          </s:code-pane>
+        </s:code-panes>
+      </s:group>
+    </s:section>
+
     <s:section title="Advanced select" description="${%usage.1}">
       <s:group>
         <s:preview>

src/main/resources/io/jenkins/plugins/designlibrary/Select/index.properties

@@ -8,3 +8,4 @@ searchable=Autocomplete
 searchable.description=Allows users to quickly browse a select by typing to filter the available choices. Start typing a U.S. state for results to appear.
 combobox=Using <code>combobox</code> forces the user to select an option from the available choices, it''ll also display all choices on focus.
 textbox=Using <code>textbox</code> on the other hand allows the user to enter free text if they so desire.
+usage.enum=With <code>f:enum</code> you can create a select that is based on an <code>enum</code> in Java.

src/main/webapp/Select/Enum.java

@@ -0,0 +1,31 @@
+public class UnitHolder {
+
+    private Unit unit;
+
+    public Unit getUnit() {
+        return unit;
+    }
+
+    @DataBoundSetter
+    public void setUnit(Unit unit) {
+        this.unit = unit
+    }
+
+    public enum Unit {
+        MILLISECONDS("Milliseconds"),
+        SECONDS("Seconds"),
+        MINUTES("Minutes"),
+        HOURS("Hours"),
+        DAYS("Days");
+
+        private final String description;
+
+        Unit(String description) {
+            this.description = description;
+        }
+
+        public String getDescription() {
+            return description;
+        }
+    }
+}

src/main/webapp/Select/enum.jelly

@@ -0,0 +1,5 @@
+<f:entry title="Unit" field="unit">
+  <f:enum default="SECONDS">
+    ${it.description}
+  </f:enum>
+</f:entry>