make DomElement#getXmlTag nullable and adapt some clients

inspired by https://github.com/JetBrains/intellij-community/pull/796

plugins/ant/src/com/intellij/lang/ant/dom/AntDomProject.java

@@ -162,7 +162,7 @@ public abstract class AntDomProject extends AntDomNamedElement implements Proper
   }
 
   public AntInstallation getAntInstallation() {
-    final AntConfigurationBase configuration = AntConfigurationBase.getInstance(getXmlTag().getProject());
+    final AntConfigurationBase configuration = AntConfigurationBase.getInstance(getManager().getProject());
     AntInstallation antInstallation = null;
     if (configuration != null) {
       antInstallation = configuration.getProjectDefaultAnt();

plugins/devkit/devkit-core/src/dom/Extension.java

@@ -16,12 +16,18 @@
 package org.jetbrains.idea.devkit.dom;
 
 import com.intellij.ide.presentation.Presentation;
+import com.intellij.psi.xml.XmlTag;
 import com.intellij.util.xml.*;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 @Presentation(typeName = "Extension")
 public interface Extension extends DomElement {
 
+  @NotNull
+  @Override
+  XmlTag getXmlTag();
+
   @NameValue
   @Required(value = false)
   GenericAttributeValue<String> getId();

plugins/devkit/devkit-core/src/dom/ExtensionPoint.java

@@ -18,6 +18,7 @@ package org.jetbrains.idea.devkit.dom;
 import com.intellij.ide.presentation.Presentation;
 import com.intellij.psi.PsiClass;
 import com.intellij.psi.PsiField;
+import com.intellij.psi.xml.XmlTag;
 import com.intellij.util.xml.*;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -33,6 +34,11 @@ public interface ExtensionPoint extends DomElement {
     IDEA_APPLICATION
   }
 
+
+  @NotNull
+  @Override
+  XmlTag getXmlTag();
+
   @NotNull
   @Stubbed
   @NameValue

plugins/devkit/devkit-core/src/dom/Extensions.java

@@ -15,6 +15,7 @@
  */
 package org.jetbrains.idea.devkit.dom;
 
+import com.intellij.psi.xml.XmlTag;
 import com.intellij.util.xml.*;
 import org.jetbrains.annotations.NonNls;
 import org.jetbrains.annotations.NotNull;
@@ -24,6 +25,10 @@ import java.util.List;
 
 public interface Extensions extends DomElement {
 
+  @NotNull
+  @Override
+  XmlTag getXmlTag();
+
   @NonNls
   String DEFAULT_PREFIX = "com.intellij";
 

plugins/devkit/devkit-core/src/inspections/ComponentModuleRegistrationChecker.kt

@@ -99,9 +99,9 @@ fun checkProperXmlFileForExtension(element: Extension,
 
   for (childDescription in element.genericInfo.fixedChildrenDescriptions) {
     val domElement = childDescription.getValues(element).firstOrNull() ?: continue
-    val text = domElement.xmlTag?.value?.text ?: continue
-    val project = domElement.xmlTag.project
-    val psiClass = JavaPsiFacade.getInstance(project).findClass(text, GlobalSearchScope.projectScope(project))
+    val tag = domElement.xmlTag ?: continue
+    val project = tag.project
+    val psiClass = JavaPsiFacade.getInstance(project).findClass(tag.value.text, GlobalSearchScope.projectScope(project))
     if (psiClass != null && checkProperXmlFileForClass(element, holder, psiClass, ignoreClassList)) return
   }
 }

plugins/devkit/devkit-core/src/refactoring/InspectionAutomaticRenamerFactory.java

@@ -17,7 +17,6 @@ import com.intellij.psi.PsiFile;
 import com.intellij.psi.util.InheritanceUtil;
 import com.intellij.psi.xml.XmlAttribute;
 import com.intellij.psi.xml.XmlAttributeValue;
-import com.intellij.psi.xml.XmlTag;
 import com.intellij.refactoring.rename.UnresolvableCollisionUsageInfo;
 import com.intellij.refactoring.rename.naming.AutomaticRenamer;
 import com.intellij.refactoring.rename.naming.AutomaticRenamerFactory;
@@ -91,11 +90,7 @@ public class InspectionAutomaticRenamerFactory implements AutomaticRenamerFactor
   @Nullable
   private static XmlAttribute getInspectionShortNameAttribute(Module module, PsiClass inspectionClass) {
     Extension extension = InspectionDescriptionInfo.findExtension(module, inspectionClass);
-    if (extension == null) {
-      return null;
-    }
-    XmlTag tag = extension.getXmlTag();
-    return tag == null ? null : tag.getAttribute("shortName");
+    return extension == null ? null : extension.getXmlTag().getAttribute("shortName");
   }
 
   private static boolean isGetShortNameMethodOverridden(PsiClass inspectionClass) {

plugins/devkit/devkit-core/src/util/ExtensionLocator.java

@@ -21,7 +21,6 @@ import org.jetbrains.annotations.Nullable;
 import org.jetbrains.idea.devkit.dom.Extension;
 import org.jetbrains.idea.devkit.dom.ExtensionPoint;
 
-import java.util.Collections;
 import java.util.List;
 import java.util.function.BiFunction;
 
@@ -89,9 +88,6 @@ public abstract class ExtensionLocator {
     @Override
     public List<ExtensionCandidate> findCandidates() {
       XmlTag epTag = myExtensionPoint.getXmlTag();
-      if (epTag == null) {
-        return Collections.emptyList();
-      }
 
       // We must search for the last part of EP name, because for instance 'com.intellij.console.folding' extension
       // may be declared as <extensions defaultExtensionNs="com"><intellij.console.folding ...

xml/dom-openapi/src/com/intellij/util/xml/DomElement.java

@@ -36,6 +36,7 @@ import java.lang.reflect.Type;
 public interface DomElement extends AnnotatedElement, UserDataHolder {
   DomElement[] EMPTY_ARRAY = new DomElement[0];
 
+  @Nullable
   XmlTag getXmlTag();
 
   /**