Add a hook for nodes to callback if the visitor is incorrect

pmd-apex/src/main/java/net/sourceforge/pmd/lang/apex/ast/AbstractApexNode.java

@@ -42,11 +42,12 @@ abstract class AbstractApexNode<T extends AstNode> extends AbstractNodeWithTextC
     }
 
     @Override
+    @SuppressWarnings("unchecked")
     public final <P, R> R acceptVisitor(AstVisitor<? super P, ? extends R> visitor, P data) {
         if (visitor instanceof ApexVisitor) {
             return this.acceptApexVisitor((ApexVisitor<? super P, ? extends R>) visitor, data);
         }
-        return super.acceptVisitor(visitor, data);
+        return visitor.cannotVisit(this, data);
     }
 
     protected abstract <P, R> R acceptApexVisitor(ApexVisitor<? super P, ? extends R> visitor, P data);

pmd-core/src/main/java/net/sourceforge/pmd/lang/ast/AstVisitor.java

@@ -21,6 +21,22 @@ package net.sourceforge.pmd.lang.ast;
  */
 public interface AstVisitor<P, R> {
 
+
+    /**
+     * Called by a node when it detects that the visitor is not of the
+     * language it is used to visiting. If a visitor wants to visit nodes
+     * for several languages, it should provide a useful implementation
+     * of this method. The default implementation throws
+     *
+     * @param node  Node calling back this method
+     * @param param Parameter of the visit
+     *
+     * @return A value (or may throw)
+     */
+    default R cannotVisit(Node node, P param) {
+        throw new UnsupportedOperationException("Cannot visit " + node);
+    }
+
     /**
      * Visit a node. This method is dispatched statically, you should
      * use {@link Node#acceptVisitor(AstVisitor, Object)} if you want

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/ast/AbstractJavaNode.java

@@ -34,11 +34,12 @@ public abstract class AbstractJavaNode extends AbstractJjtreeNode<AbstractJavaNo
     }
 
     @Override
+    @SuppressWarnings("unchecked")
     public final <P, R> R acceptVisitor(AstVisitor<? super P, ? extends R> visitor, P data) {
         if (visitor instanceof JavaVisitor) {
             return this.acceptVisitor((JavaVisitor<? super P, ? extends R>) visitor, data);
         }
-        return super.acceptVisitor(visitor, data);
+        return visitor.cannotVisit(this, data);
     }
 
     protected abstract <P, R> R acceptVisitor(JavaVisitor<? super P, ? extends R> visitor, P data);

pmd-javascript/src/main/java/net/sourceforge/pmd/lang/ecmascript/ast/AbstractEcmascriptNode.java

@@ -50,11 +50,11 @@ abstract class AbstractEcmascriptNode<T extends AstNode> extends AbstractNodeWit
 
     @Override
     @SuppressWarnings("unchecked")
-    public <P, R> R acceptVisitor(AstVisitor<? super P, ? extends R> visitor, P data) {
-        if (!(visitor instanceof EcmascriptVisitor)) {
-            return super.acceptVisitor(visitor, data);
+    public final <P, R> R acceptVisitor(AstVisitor<? super P, ? extends R> visitor, P data) {
+        if (visitor instanceof EcmascriptVisitor) {
+            return acceptJsVisitor((EcmascriptVisitor<? super P, ? extends R>) visitor, data);
         }
-        return acceptJsVisitor((EcmascriptVisitor<? super P, ? extends R>) visitor, data);
+        return visitor.cannotVisit(this, data);
     }
 
     protected abstract <P, R> R acceptJsVisitor(EcmascriptVisitor<? super P, ? extends R> visitor, P data);

pmd-jsp/src/main/java/net/sourceforge/pmd/lang/jsp/ast/AbstractJspNode.java

@@ -14,11 +14,12 @@ abstract class AbstractJspNode extends AbstractJjtreeNode<AbstractJspNode, JspNo
     }
 
     @Override
+    @SuppressWarnings("unchecked")
     public final <P, R> R acceptVisitor(AstVisitor<? super P, ? extends R> visitor, P data) {
         if (visitor instanceof JspVisitor) {
             return this.acceptVisitor((JspVisitor<? super P, ? extends R>) visitor, data);
         }
-        return super.acceptVisitor(visitor, data);
+        return visitor.cannotVisit(this, data);
     }
 
     protected abstract <P, R> R acceptVisitor(JspVisitor<? super P, ? extends R> visitor, P data);

pmd-modelica/src/main/java/net/sourceforge/pmd/lang/modelica/ast/AbstractModelicaNode.java

@@ -4,6 +4,7 @@
 
 package net.sourceforge.pmd.lang.modelica.ast;
 
+import net.sourceforge.pmd.lang.ast.AstVisitor;
 import net.sourceforge.pmd.lang.ast.impl.javacc.AbstractJjtreeNode;
 import net.sourceforge.pmd.lang.modelica.resolver.ModelicaScope;
 
@@ -31,6 +32,15 @@ abstract class AbstractModelicaNode extends AbstractJjtreeNode<AbstractModelicaN
     }
 
 
+    @Override
+    @SuppressWarnings("unchecked")
+    public final <P, R> R acceptVisitor(AstVisitor<? super P, ? extends R> visitor, P data) {
+        if (visitor instanceof ModelicaVisitor) {
+            return acceptModelicaVisitor((ModelicaVisitor<? super P, ? extends R>) visitor, data);
+        }
+        return visitor.cannotVisit(this, data);
+    }
+
     protected abstract <P, R> R acceptModelicaVisitor(ModelicaVisitor<? super P, ? extends R> visitor, P data);
 
     @Override

pmd-scala-modules/pmd-scala-common/src/main/java/net/sourceforge/pmd/lang/scala/ast/AbstractScalaNode.java

@@ -34,11 +34,12 @@ abstract class AbstractScalaNode<T extends Tree> extends AbstractNode<AbstractSc
     }
 
     @Override
+    @SuppressWarnings("unchecked")
     public <P, R> R acceptVisitor(AstVisitor<? super P, ? extends R> visitor, P data) {
         if (visitor instanceof ScalaParserVisitor) {
             return this.acceptVisitor((ScalaParserVisitor<P, R>) visitor, data);
         }
-        return super.acceptVisitor(visitor, data);
+        return visitor.cannotVisit(this, data);
     }
 
     protected abstract <P, R> R acceptVisitor(ScalaParserVisitor<? super P, ? extends R> visitor, P data);