[javadoc] Add navigation for fragment references

#IDEA-376337 Fixed

GitOrigin-RevId: e56328231c555d8cf4a75a93b107a1e284f15c73

java/java-psi-impl/src/com/intellij/core/CoreJavaPsiImplementationHelper.java

@@ -1,4 +1,4 @@
-// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+// Copyright 2000-2025 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package com.intellij.core;
 
 import com.intellij.lang.ASTNode;
@@ -9,6 +9,7 @@ import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.pom.java.LanguageLevel;
 import com.intellij.psi.*;
 import com.intellij.psi.impl.JavaPsiImplementationHelper;
+import com.intellij.psi.impl.source.javadoc.PsiDocFragmentName;
 import com.intellij.psi.javadoc.PsiDocToken;
 import com.intellij.psi.javadoc.PsiSnippetAttributeValue;
 import com.intellij.psi.util.PsiUtil;
@@ -85,6 +86,11 @@ public class CoreJavaPsiImplementationHelper extends JavaPsiImplementationHelper
     throw new UnsupportedOperationException();
   }
 
+  @Override
+  public @Nullable PsiSymbolReference getFragmentNameSymbol(@NotNull PsiDocFragmentName token) {
+    throw new UnsupportedOperationException();
+  }
+
   public @NotNull Project getProject() {
     return myProject;
   }

java/java-psi-impl/src/com/intellij/psi/impl/JavaPsiImplementationHelper.java

@@ -1,4 +1,4 @@
-// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+// Copyright 2000-2025 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package com.intellij.psi.impl;
 
 import com.intellij.lang.ASTNode;
@@ -7,6 +7,7 @@ import com.intellij.openapi.project.Project;
 import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.pom.java.LanguageLevel;
 import com.intellij.psi.*;
+import com.intellij.psi.impl.source.javadoc.PsiDocFragmentName;
 import com.intellij.psi.javadoc.PsiDocToken;
 import com.intellij.psi.javadoc.PsiSnippetAttributeValue;
 import org.jetbrains.annotations.NotNull;
@@ -42,4 +43,9 @@ public abstract class JavaPsiImplementationHelper {
    * This makes it possible to navigate to the inherited doc.
    */
   public abstract @NotNull PsiSymbolReference getInheritDocSymbol(@NotNull PsiDocToken token);
+
+  /**
+   * Returns a PsiSymbolReference mapping a fragment reference ({@code ##fragment-id}) to its source ({@code <p id="fragment-id">…</p>}).
+   */
+  public abstract @Nullable PsiSymbolReference getFragmentNameSymbol(@NotNull PsiDocFragmentName token);
 }

java/java-psi-impl/src/com/intellij/psi/impl/source/javadoc/PsiDocFragmentName.java

@@ -1,12 +1,20 @@
 // Copyright 2000-2025 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package com.intellij.psi.impl.source.javadoc;
 
+import com.intellij.model.psi.PsiSymbolReference;
 import com.intellij.psi.JavaElementVisitor;
+import com.intellij.psi.PsiClass;
+import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiElementVisitor;
+import com.intellij.psi.impl.JavaPsiImplementationHelper;
 import com.intellij.psi.impl.source.Constants;
 import com.intellij.psi.impl.source.tree.CompositePsiElement;
 import com.intellij.psi.javadoc.PsiDocTagValue;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Collection;
+import java.util.Collections;
 
 public class PsiDocFragmentName extends CompositePsiElement implements PsiDocTagValue, Constants {
   public PsiDocFragmentName() {
@@ -22,4 +30,19 @@ public class PsiDocFragmentName extends CompositePsiElement implements PsiDocTag
       visitor.visitElement(this);
     }
   }
+
+  public @Nullable PsiClass getScope() {
+    final PsiElement parent = getParent();
+    return parent instanceof PsiDocFragmentRef ? ((PsiDocFragmentRef)parent).getScope() : null;
+  }
+
+  @Override
+  public @NotNull Collection<? extends @NotNull PsiSymbolReference> getOwnReferences() {
+    final PsiSymbolReference symbolReference = JavaPsiImplementationHelper
+      .getInstance(getProject())
+      .getFragmentNameSymbol(this);
+
+    if (symbolReference != null) return Collections.singleton(symbolReference);
+    return super.getOwnReferences();
+  }
 }