IDEA-45809 XML editing: Required attributes should be preferred in completion

xml/impl/src/com/intellij/psi/impl/source/html/dtd/HtmlAttributeDescriptorImpl.java

@@ -85,4 +85,9 @@ public class HtmlAttributeDescriptorImpl implements XmlAttributeDescriptor {
   public Object[] getDependences() {
     return ArrayUtil.EMPTY_OBJECT_ARRAY;
   }
+
+  @Override
+  public String toString() {
+    return delegate.toString();
+  }
 }

xml/impl/src/com/intellij/psi/impl/source/xml/XmlAttributeImpl.java

@@ -416,8 +416,6 @@ public class XmlAttributeImpl extends XmlElementImpl implements XmlAttribute {
       return setName(newName);
     }
 
-    // TODO[ik]: namespace support
-
     public PsiElement bindToElement(@NotNull PsiElement element) throws IncorrectOperationException {
       if (element instanceof PsiMetaOwner) {
         final PsiMetaOwner owner = (PsiMetaOwner)element;
@@ -475,7 +473,8 @@ public class XmlAttributeImpl extends XmlElementImpl implements XmlAttribute {
             if (separator > 0) {
               element = element.withLookupString(name.substring(separator + 1));
             }
-            variants.add(element.withCaseSensitivity(caseSensitive).withInsertHandler(XmlAttributeInsertHandler.INSTANCE));
+            element = element.withCaseSensitivity(caseSensitive).withInsertHandler(XmlAttributeInsertHandler.INSTANCE);
+            variants.add(descriptor.isRequired() ? PrioritizedLookupElement.withPriority(element.appendTailText("(required)", true), 100) : element);
           }
         }
       }

xml/impl/src/com/intellij/xml/impl/BasicXmlAttributeDescriptor.java

@@ -73,4 +73,9 @@ public abstract class BasicXmlAttributeDescriptor implements XmlAttributeDescrip
   public boolean isEnumerated(@Nullable XmlElement context) {
     return isEnumerated();
   }
+
+  @Override
+  public String toString() {
+    return getName();
+  }
 }

xml/impl/src/com/intellij/xml/impl/schema/XmlAttributeDescriptorImpl.java

@@ -243,9 +243,4 @@ public class XmlAttributeDescriptorImpl extends BasicXmlAttributeDescriptor impl
   public void setName(String name) throws IncorrectOperationException {
     NamedObjectDescriptor.setName(myTag, name);
   }
-
-  @Override
-  public String toString() {
-    return getName();
-  }
 }

xml/tests/src/com/intellij/codeInsight/completion/XmlCompletionTest.java

@@ -636,5 +636,15 @@ public class XmlCompletionTest extends LightCodeInsightFixtureTestCase {
                        "xsi:noNamespaceSchemaLocation",
                        "xsi:type");
   }
+
+  public void testRequiredAttributesOnTop() throws Exception {
+    myFixture.configureByText("foo.html", "<img <caret>");
+    myFixture.completeBasic();
+    List<String> strings = myFixture.getLookupElementStrings();
+    assertNotNull(strings);
+    assertEquals("alt", strings.get(0));
+    assertEquals("src", strings.get(1));
+    assertEquals("align", strings.get(2));
+  }
 }