IDEA-176694 redundant attribute inspection ignores the fixed attribute in xml schema

xml/tests/src/com/intellij/codeInsight/daemon/XmlInspectionsTest.java

@@ -19,8 +19,11 @@ import com.intellij.codeInsight.daemon.impl.analysis.XmlDefaultAttributeValueIns
 import com.intellij.codeInsight.intention.IntentionAction;
 import com.intellij.ide.highlighter.HtmlFileType;
 import com.intellij.ide.highlighter.XmlFileType;
+import com.intellij.testFramework.PlatformTestUtil;
 import com.intellij.testFramework.fixtures.LightPlatformCodeInsightFixtureTestCase;
 
+import java.io.File;
+
 /**
  * @author Dmitry Avdeev
  */
@@ -63,4 +66,14 @@ public class XmlInspectionsTest extends LightPlatformCodeInsightFixtureTestCase
     myFixture.configureByText(HtmlFileType.INSTANCE, "<input type=\"text\"/>");
     myFixture.checkHighlighting();
   }
+
+  public void testRequiredFixedAttribute() {
+    myFixture.enableInspections(new XmlDefaultAttributeValueInspection());
+    myFixture.testHighlighting("def.xml", "def.xsd");
+  }
+
+  @Override
+  protected String getTestDataPath() {
+    return PlatformTestUtil.getCommunityPath().replace(File.separatorChar, '/') + "/xml/tests/testData/xml";
+  }
 }

xml/tests/testData/xml/def.xml

@@ -0,0 +1 @@
+<root xmlns="test.required" required="foo" fixed=<warning descr="Redundant default attribute value assignment">"foo"</warning>/>

xml/tests/testData/xml/def.xsd

@@ -0,0 +1,8 @@
+<schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="test.required">
+    <element name="root">
+        <complexType>
+            <attribute name="required" fixed="foo" use="required"/>
+            <attribute name="fixed" fixed="foo"/>
+        </complexType>
+    </element>
+</schema>

xml/xml-analysis-impl/src/com/intellij/codeInsight/daemon/impl/analysis/XmlDefaultAttributeValueInspection.java

@@ -46,7 +46,7 @@ public class XmlDefaultAttributeValueInspection extends XmlSuppressableInspectio
         }
         if (parent.getParent() instanceof HtmlTag) return;
         XmlAttributeDescriptor descriptor = ((XmlAttribute)parent).getDescriptor();
-        if (descriptor == null) {
+        if (descriptor == null || descriptor.isRequired()) {
           return;
         }
         String defaultValue = descriptor.getDefaultValue();