Navigatable custom regions in XML/HTML structure view [IDEA-CR-16020]

platform/core-api/src/com/intellij/lang/folding/CustomFoldingBuilder.java

@@ -212,6 +212,10 @@ public abstract class CustomFoldingBuilder extends FoldingBuilderEx implements P
     return node.getPsi() instanceof PsiComment;
   }
 
+  public final boolean isCustomFoldingCandidate(@NotNull PsiElement element) {
+    return isCustomFoldingCandidate(element.getNode());
+  }
+
   /**
    * Checks if the node is used as custom folding root. Any custom folding elements inside the root are considered to be at the same level
    * even if they are located at different levels of PSI tree. By default the method returns true if the node has any child elements

platform/structure-view-impl/src/com/intellij/ide/structureView/customRegions/CustomRegionStructureUtil.java

@@ -17,7 +17,8 @@ package com.intellij.ide.structureView.customRegions;
 
 import com.intellij.ide.structureView.StructureViewTreeElement;
 import com.intellij.lang.ASTNode;
-import com.intellij.lang.folding.CustomFoldingProvider;
+import com.intellij.lang.Language;
+import com.intellij.lang.folding.*;
 import com.intellij.openapi.util.TextRange;
 import com.intellij.psi.*;
 import com.intellij.util.containers.ContainerUtil;
@@ -130,6 +131,22 @@ public class CustomRegionStructureUtil {
   }
 
   private static boolean isCustomRegionCommentCandidate(@NotNull PsiElement element) {
-    return element instanceof PsiComment && !element.textContains('\n');
+    Language language = element.getLanguage();
+    if (!Language.ANY.is(language)) {
+      final FoldingBuilder foldingBuilder = LanguageFolding.INSTANCE.forLanguage(language);
+      if (foldingBuilder instanceof CustomFoldingBuilder) {
+        return ((CustomFoldingBuilder)foldingBuilder).isCustomFoldingCandidate(element);
+      }
+      else if (foldingBuilder instanceof CompositeFoldingBuilder) {
+        for (FoldingBuilder simpleBuilder : ((CompositeFoldingBuilder)foldingBuilder).getAllBuilders()) {
+          if (simpleBuilder instanceof CustomFoldingBuilder) {
+            if (((CustomFoldingBuilder)simpleBuilder).isCustomFoldingCandidate(element)) {
+              return true;
+            }
+          }
+        }
+      }
+    }
+    return false;
   }
 }

platform/structure-view-impl/src/com/intellij/ide/structureView/customRegions/CustomRegionTreeElement.java

@@ -152,4 +152,8 @@ public class CustomRegionTreeElement implements StructureViewTreeElement {
     return myParent;
   }
 
+  @Override
+  public String toString() {
+    return "Region '" + myProvider.getPlaceholderText(myStartElement.getText()) + "'";
+  }
 }

xml/xml-psi-impl/src/com/intellij/psi/impl/source/xml/XmlTokenImpl.java

@@ -83,8 +83,18 @@ public class XmlTokenImpl extends LeafPsiElement implements XmlToken, Navigatabl
     return super.getReferences();
   }
 
+  @Override
+  public PsiElement getNavigationElement() {
+    if (getTokenType() == XmlTokenType.XML_COMMENT_CHARACTERS) {
+      PsiElement parent = this.getParent();
+      return parent != null ? parent : this;
+    }
+    return super.getNavigationElement();
+  }
+
   @Override
   public boolean canNavigate() {
-    return getTokenType() == XmlTokenType.XML_NAME && PsiNavigationSupport.getInstance().canNavigate(this);
+    return getTokenType() == XmlTokenType.XML_NAME && PsiNavigationSupport.getInstance().canNavigate(this) ||
+           getTokenType() == XmlTokenType.XML_COMMENT_CHARACTERS; // Custom regions
   }
 }