Support getters from default methods in interfaces.

Fortunately this did not require using any JDK 1.8-specific APIs, just
searching (via reflection) through the set of interfaces implemented by a class
in addition to its super-classes.

One downside is that the transitive set of all implemented interfaces could be
much larger than the super-class chain, but this is the last thing we search,
so in theory we only even get here if we were about to fail to find the getter
entirely.

This also means that our tests have to be compiled and run with Java 8, because
I was not in the mood to figure out how to do all the complex Maven jockeying
to have a special JDK8 profile and disable JDK8 tests in the normal profile and
re-enable them in the JDK8 profile and blah blah blah, just shoot me now.

.travis.yml

@@ -3,9 +3,8 @@ sudo: false
 language: java
 
 jdk:
-  - oraclejdk7
+  - oraclejdk8
-  - openjdk7
+  - openjdk8
-  - openjdk6
 
 cache:
   directories:

pom.xml

@@ -91,6 +91,8 @@
         <configuration>
           <source>1.6</source>
           <target>1.6</target>
+          <testSource>1.8</testSource>
+          <testTarget>1.8</testTarget>
           <fork>true</fork>
           <showDeprecation>true</showDeprecation>
           <showWarnings>true</showWarnings>
@@ -101,6 +103,7 @@
           </compilerArgs>
         </configuration>
       </plugin>
+
       <plugin>
         <groupId>org.apache.felix</groupId>
         <artifactId>maven-bundle-plugin</artifactId>
@@ -115,6 +118,7 @@
           </instructions>
         </configuration>
       </plugin>
+
 <!-- disabled due to src/main/gwt related hoseage
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
@@ -132,6 +136,7 @@
         </executions>
       </plugin>
 -->
+
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-resources-plugin</artifactId>
@@ -140,6 +145,7 @@
           <encoding>UTF-8</encoding>
         </configuration>
       </plugin>
+
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-surefire-plugin</artifactId>
@@ -148,6 +154,7 @@
           <includes><include>**/*Test.java</include></includes>
         </configuration>
       </plugin>
+
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-javadoc-plugin</artifactId>
@@ -158,6 +165,7 @@
           <additionalparam>-Xdoclint:all -Xdoclint:-missing</additionalparam>
         </configuration>
       </plugin>
+
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-jar-plugin</artifactId>
@@ -184,6 +192,7 @@
           <maxmem>256m</maxmem>
         </configuration>
       </plugin>
+
       <plugin>
         <groupId>org.eluder.coveralls</groupId>
         <artifactId>coveralls-maven-plugin</artifactId>

src/main/java/com/samskivert/mustache/DefaultCollector.java

@@ -10,7 +10,9 @@ import java.lang.reflect.Method;
 
 import java.util.AbstractList;
 import java.util.Iterator;
+import java.util.LinkedHashSet;
 import java.util.Map;
+import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 
 /**
@@ -41,6 +43,7 @@ public class DefaultCollector extends BasicCollector
         Mustache.VariableFetcher fetcher = super.createFetcher(ctx, name);
         if (fetcher != null) return fetcher;
 
+        // first check for a getter which provides the value
         Class<?> cclass = ctx.getClass();
         final Method m = getMethod(cclass, name);
         if (m != null) {
@@ -51,6 +54,7 @@ public class DefaultCollector extends BasicCollector
             };
         }
 
+        // next check for a getter which provides the value
         final Field f = getField(cclass, name);
         if (f != null) {
             return new Mustache.VariableFetcher() {
@@ -60,6 +64,17 @@ public class DefaultCollector extends BasicCollector
             };
         }
 
+        // finally check for a default interface method which provides the value (this is left to
+        // last because it's much more expensive and hopefully something already matched above)
+        final Method im = getIfaceMethod(cclass, name);
+        if (im != null) {
+            return new Mustache.VariableFetcher() {
+                public Object get (Object ctx, String name) throws Exception {
+                    return im.invoke(ctx);
+                }
+            };
+        }
+
         return null;
     }
 
@@ -69,15 +84,38 @@ public class DefaultCollector extends BasicCollector
     }
 
     protected Method getMethod (Class<?> clazz, String name) {
+        // first check up the superclass chain
+        for (Class<?> cc = clazz; cc != null && cc != Object.class; cc = cc.getSuperclass()) {
+            Method m = getMethodOn(cc, name);
+            if (m != null) return m;
+        }
+        return null;
+    }
+
+    protected Method getIfaceMethod (Class<?> clazz, String name) {
+        // enumerate the transitive closure of all interfaces implemented by clazz
+        Set<Class<?>> ifaces = new LinkedHashSet<Class<?>>();
+        for (Class<?> cc = clazz; cc != null && cc != Object.class; cc = cc.getSuperclass()) {
+            addIfaces(ifaces, cc, false);
+        }
+        // now search those in the order that we found them
+        for  (Class<?> iface : ifaces) {
+            Method m = getMethodOn(iface, name);
+            if (m != null) return m;
+        }
+        return null;
+    }
+
+    private void addIfaces (Set<Class<?>> ifaces, Class<?> clazz, boolean isIface) {
+        if (isIface) ifaces.add(clazz);
+        for (Class<?> iface : clazz.getInterfaces()) addIfaces(ifaces, iface, true);
+    }
+
+    protected Method getMethodOn (Class<?> clazz, String name) {
         Method m;
         try {
             m = clazz.getDeclaredMethod(name);
-            if (!m.getReturnType().equals(void.class)) {
+            if (!m.getReturnType().equals(void.class)) return makeAccessible(m);
-                if (!m.isAccessible()) {
-                    m.setAccessible(true);
-                }
-                return m;
-            }
         } catch (Exception e) {
             // fall through
         }
@@ -85,12 +123,7 @@ public class DefaultCollector extends BasicCollector
         String upperName = Character.toUpperCase(name.charAt(0)) + name.substring(1);
         try {
             m = clazz.getDeclaredMethod("get" + upperName);
-            if (!m.getReturnType().equals(void.class)) {
+            if (!m.getReturnType().equals(void.class)) return makeAccessible(m);
-                if (!m.isAccessible()) {
-                    m.setAccessible(true);
-                }
-                return m;
-            }
         } catch (Exception e) {
             // fall through
         }
@@ -98,23 +131,19 @@ public class DefaultCollector extends BasicCollector
         try {
             m = clazz.getDeclaredMethod("is" + upperName);
             if (m.getReturnType().equals(boolean.class) ||
-                m.getReturnType().equals(Boolean.class)) {
+                m.getReturnType().equals(Boolean.class)) return makeAccessible(m);
-                if (!m.isAccessible()) {
-                    m.setAccessible(true);
-                }
-                return m;
-            }
         } catch (Exception e) {
             // fall through
         }
 
-        Class<?> sclass = clazz.getSuperclass();
-        if (sclass != Object.class && sclass != null) {
-            return getMethod(clazz.getSuperclass(), name);
-        }
         return null;
     }
 
+    private Method makeAccessible (Method m) {
+        if (!m.isAccessible()) m.setAccessible(true);
+        return m;
+    }
+
     protected Field getField (Class<?> clazz, String name) {
         Field f;
         try {

src/test/java/com/samskivert/mustache/MustacheTest.java

@@ -41,6 +41,22 @@ public class MustacheTest
         });
     }
 
+    public interface HasDefault {
+        default String getFoo () { return "bar"; }
+    }
+    public interface Interloper extends HasDefault {
+        default String getFoo () { return "bang"; }
+    }
+    @Test public void testDefaultMethodVariable () {
+        test("bar", "{{foo}}", new HasDefault() {
+        });
+        test("bang", "{{foo}}", new Interloper() {
+        });
+        test("bong", "{{foo}}", new Interloper() {
+            public String getFoo () { return "bong"; }
+        });
+    }
+
     @Test public void testPropertyVariable () {
         test("bar", "{{foo}}", new Object() {
             String getFoo () { return "bar"; }