api usage inspection: warn if old interface method was made default and class doesn't override it

java/java-tests/testData/inspection/usage1.5/defaultMethods/expected.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<problems>
+  <problem>
+    <file>Test.java</file>
+    <line>3</line>
+    <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Usages of API documented as @since 1.5 (1.6|1.7)</problem_class>
+    <description>Default method 'remove' is not overridden. It would cause compilation problems with JDK 6</description>
+  </problem>
+
+</problems>

java/java-tests/testData/inspection/usage1.5/defaultMethods/src/Test.java

@@ -0,0 +1,29 @@
+import java.util.Iterator;
+
+public class Test implements Iterator<String> {
+  @Override
+  public boolean hasNext() {
+    return false;
+  }
+
+  @Override
+  public String next() {
+    return null;
+  }
+
+  static class T implements Iterator<String> {
+    @Override
+    public boolean hasNext() {
+      return false;
+    }
+
+    @Override
+    public String next() {
+      return null;
+    }
+
+    @Override
+    public void remove() {}
+  }
+}
+

java/java-tests/testSrc/com/intellij/codeInspection/JavaAPIUsagesInspectionTest.java

@@ -23,6 +23,7 @@ package com.intellij.codeInspection;
 import com.intellij.JavaTestUtil;
 import com.intellij.codeInspection.ex.LocalInspectionToolWrapper;
 import com.intellij.codeInspection.java15api.Java15APIUsageInspection;
+import com.intellij.openapi.projectRoots.Sdk;
 import com.intellij.pom.java.LanguageLevel;
 import com.intellij.testFramework.IdeaTestUtil;
 import com.intellij.testFramework.InspectionTestCase;
@@ -60,6 +61,20 @@ public class JavaAPIUsagesInspectionTest extends InspectionTestCase {
     });
   }
 
+  public void testDefaultMethods() throws Exception {
+    IdeaTestUtil.withLevel(getModule(), LanguageLevel.JDK_1_6, new Runnable() {
+      @Override
+      public void run() {
+        doTest();
+      }
+    });
+  }
+
+  @Override
+  protected Sdk getTestProjectSdk() {
+    return IdeaTestUtil.getMockJdk18();
+  }
+
   //generate apiXXX.txt
   /*
   public void testCollectSinceApiUsages() {