implemented optional dependencies

Plugin authors could now define optional dependencies to other plugins in their pom.
Extensions which are using classes from optional dependencies must specify this
with the "requires" attribute of the extension annotation.
Extensions with "requires" attribute are not installed if one of the specified plugins,
is not installed.

scm-webapp/src/test/java/sonia/scm/plugin/PluginTreeTest.java

@@ -34,6 +34,7 @@ package sonia.scm.plugin;
 //~--- non-JDK imports --------------------------------------------------------
 
 import com.google.common.base.Function;
+import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Lists;
 
 import org.junit.Rule;
@@ -72,7 +73,7 @@ public class PluginTreeTest
     PluginCondition condition = new PluginCondition("999",
                                   new ArrayList<String>(), "hit");
     InstalledPluginDescriptor plugin = new InstalledPluginDescriptor(2, createInfo("a",  "1"), null, condition,
-                      false, null);
+                      false, null, null);
     ExplodedSmp smp = createSmp(plugin);
 
     new PluginTree(smp).getRootNodes();
@@ -115,7 +116,7 @@ public class PluginTreeTest
   public void testScmVersion() throws IOException
   {
     InstalledPluginDescriptor plugin = new InstalledPluginDescriptor(1, createInfo("a", "1"), null, null, false,
-                      null);
+                      null, null);
     ExplodedSmp smp = createSmp(plugin);
 
     new PluginTree(smp).getRootNodes();
@@ -131,10 +132,10 @@ public class PluginTreeTest
   public void testSimpleDependencies() throws IOException
   {
     //J-
-    ExplodedSmp[] smps = new ExplodedSmp[] { 
+    ExplodedSmp[] smps = new ExplodedSmp[] {
       createSmpWithDependency("a"),
       createSmpWithDependency("b", "a"),
-      createSmpWithDependency("c", "a", "b") 
+      createSmpWithDependency("c", "a", "b")
     };
     //J+
 
@@ -152,6 +153,61 @@ public class PluginTreeTest
     assertThat(unwrapIds(b.getChildren()), containsInAnyOrder("c"));
   }
 
+  @Test
+  public void testWithOptionalDependency() throws IOException {
+    ExplodedSmp[] smps = new ExplodedSmp[] {
+      createSmpWithDependency("a"),
+      createSmpWithDependency("b", null, ImmutableSet.of("a")),
+      createSmpWithDependency("c", null, ImmutableSet.of("a", "b"))
+    };
+
+    PluginTree tree = new PluginTree(smps);
+    List<PluginNode> rootNodes = tree.getRootNodes();
+
+    assertThat(unwrapIds(rootNodes), containsInAnyOrder("a"));
+
+    PluginNode a = rootNodes.get(0);
+    assertThat(unwrapIds(a.getChildren()), containsInAnyOrder("b", "c"));
+
+    PluginNode b = a.getChild("b");
+    assertThat(unwrapIds(b.getChildren()), containsInAnyOrder("c"));
+  }
+
+  @Test
+  public void testWithDeepOptionalDependency() throws IOException {
+    ExplodedSmp[] smps = new ExplodedSmp[] {
+      createSmpWithDependency("a"),
+      createSmpWithDependency("b", "a"),
+      createSmpWithDependency("c", null, ImmutableSet.of("b"))
+    };
+
+    PluginTree tree = new PluginTree(smps);
+
+    System.out.println(tree);
+
+    List<PluginNode> rootNodes = tree.getRootNodes();
+
+    assertThat(unwrapIds(rootNodes), containsInAnyOrder("a"));
+
+    PluginNode a = rootNodes.get(0);
+    assertThat(unwrapIds(a.getChildren()), containsInAnyOrder("b"));
+
+    PluginNode b = a.getChild("b");
+    assertThat(unwrapIds(b.getChildren()), containsInAnyOrder("c"));
+  }
+
+  @Test
+  public void testWithNonExistentOptionalDependency() throws IOException {
+    ExplodedSmp[] smps = new ExplodedSmp[] {
+      createSmpWithDependency("a", null, ImmutableSet.of("b"))
+    };
+
+    PluginTree tree = new PluginTree(smps);
+    List<PluginNode> rootNodes = tree.getRootNodes();
+
+    assertThat(unwrapIds(rootNodes), containsInAnyOrder("a"));
+  }
+
   /**
    * Method description
    *
@@ -200,7 +256,7 @@ public class PluginTreeTest
   private ExplodedSmp createSmp(String name) throws IOException
   {
     return createSmp(new InstalledPluginDescriptor(2, createInfo(name, "1.0.0"), null, null,
-      false, null));
+      false, null, null));
   }
 
   /**
@@ -224,10 +280,19 @@ public class PluginTreeTest
     {
       dependencySet.add(d);
     }
+    return createSmpWithDependency(name, dependencySet, null);
+  }
 
-    InstalledPluginDescriptor plugin = new InstalledPluginDescriptor(2, createInfo(name, "1"), null, null,
-                      false, dependencySet);
-
+  private ExplodedSmp createSmpWithDependency(String name, Set<String> dependencies, Set<String> optionalDependencies) throws IOException {
+    InstalledPluginDescriptor plugin = new InstalledPluginDescriptor(
+      2,
+      createInfo(name, "1"),
+      null,
+      null,
+      false,
+      dependencies,
+      optionalDependencies
+    );
     return createSmp(plugin);
   }