snapshot

runtime/Java/src/org/antlr/v4/runtime/tree/ParseTreeVisitor.java

@@ -8,7 +8,12 @@ public class ParseTreeVisitor<T> {
 		return ctx.accept(this);
 	}
 
-	/** Visit all rule, nonleaf children */
+	/** Visit all rule, nonleaf children. Not useful if you are using T as
+	 *  non-Void.  This returns nothing, losing all computations from below.
+	 *  But handy if you are just walking the tree with a visitor and only
+	 *  care about some nodes.  The ParserRuleContext.accept() method
+	 *  walks all children by default; i.e., calls this method.
+	 */
 	public <Symbol> void visitChildren(ParserRuleContext<Symbol> ctx) {
 		for (ParseTree c : ctx.children) {
 			if ( c instanceof ParseTree.RuleNode) {

tool/playground/ABaseVisitor.java

@@ -1,11 +1,10 @@
+import org.antlr.v4.runtime.tree.*;
 import org.antlr.v4.runtime.Token;
-import org.antlr.v4.runtime.tree.ParseTreeVisitor;
 
 public class ABaseVisitor<T> extends ParseTreeVisitor<T> implements AVisitor<T> {
-	public T visit(AParser.MultContext ctx) { return null; }
+	public T visit(AParser.MultContext ctx) { visitChildren(ctx); return null; }
-	public T visit(AParser.ParensContext ctx) { return null; }
+	public T visit(AParser.ParensContext ctx) { visitChildren(ctx); return null; }
-	public T visit(AParser.eContext ctx) { return null; }
+	public T visit(AParser.sContext ctx) { visitChildren(ctx); return null; }
-	public T visit(AParser.sContext ctx) { return null; }
+	public T visit(AParser.AddContext ctx) { visitChildren(ctx); return null; }
-	public T visit(AParser.AddContext ctx) { return null; }
+	public T visit(AParser.IntContext ctx) { visitChildren(ctx); return null; }
-	public T visit(AParser.IntContext ctx) { return null; }
+}
-}

tool/playground/AVisitor.java

@@ -1,3 +1,6 @@
+import org.antlr.v4.runtime.tree.*;
+import org.antlr.v4.runtime.Token;
+
 public interface AVisitor<T> {
 	T visit(AParser.MultContext ctx);
 	T visit(AParser.ParensContext ctx);

tool/playground/TestVisitor.java

@@ -31,7 +31,7 @@ import org.antlr.v4.runtime.*;
 import org.antlr.v4.runtime.tree.ParseTreeVisitor;
 
 public class TestVisitor {
-	public static class MyVisitor extends ParseTreeVisitor<Integer> implements AVisitor<Integer> {
+	public static class MyVisitor extends ABaseVisitor<Integer> implements AVisitor<Integer> {
 		@Override
 		public Integer visit(AParser.AddContext ctx) {
 			return ctx.e(0).accept(this) + ctx.e(1).accept(this);

tool/resources/org/antlr/v4/tool/templates/codegen/Java/Java.stg

@@ -67,6 +67,16 @@ T visit(<file.parserName>.<lname>Context ctx);}; separator="\n">
 }
 >>
 
+BaseVisitorFile(file, header) ::= <<
+<header>
+import org.antlr.v4.runtime.tree.*;
+import org.antlr.v4.runtime.Token;
+
+public class <file.grammarName>BaseVisitor\<T> extends ParseTreeVisitor\<T> implements <file.grammarName>Visitor\<T> {
+	<file.visitorNames:{lname |
+public T visit(<file.parserName>.<lname>Context ctx) { visitChildren(ctx); return null; \}}; separator="\n">
+}
+>>
 
 Parser(parser, funcs, atn, sempredFuncs, superclass) ::= <<
 <Parser_(ctor="parser_ctor", ...)>

tool/src/org/antlr/v4/codegen/CodeGenPipeline.java

@@ -48,8 +48,9 @@ public class CodeGenPipeline {
 			gen.writeRecognizer(gen.generateParser());
 			if ( g.tool.gen_listener) {
 				gen.writeListener(gen.generateListener());
+				gen.writeBaseListener(gen.generateBaseListener());
 				gen.writeVisitor(gen.generateVisitor());
-				gen.writeBlankListener(gen.generateBlankListener());
+				gen.writeBaseVisitor(gen.generateBaseVisitor());
 			}
 			gen.writeHeaderFile();
 		}

tool/src/org/antlr/v4/codegen/CodeGenerator.java

@@ -182,16 +182,29 @@ public class CodeGenerator {
 		return st;
 	}
 
-	public ST generateBlankListener() {
+	public ST generateBaseListener() {
 		OutputModelFactory factory = new ParserFactory(this);
 
 		OutputModelController controller = new OutputModelController(factory);
 		factory.setController(controller);
 
-		OutputModelObject blankModel = controller.buildBlankListenerOutputModel();
+		OutputModelObject baseModel = controller.buildBaseListenerOutputModel();
 
 		OutputModelWalker walker = new OutputModelWalker(tool, templates);
-		ST st = walker.walk(blankModel);
+		ST st = walker.walk(baseModel);
+		return st;
+	}
+
+	public ST generateBaseVisitor() {
+		OutputModelFactory factory = new ParserFactory(this);
+
+		OutputModelController controller = new OutputModelController(factory);
+		factory.setController(controller);
+
+		OutputModelObject baseModel = controller.buildBaseVisitorOutputModel();
+
+		OutputModelWalker walker = new OutputModelWalker(tool, templates);
+		ST st = walker.walk(baseModel);
 		return st;
 	}
 
@@ -235,14 +248,18 @@ public class CodeGenerator {
 		target.genFile(g,outputFileST, getListenerFileName());
 	}
 
-	public void writeBlankListener(ST outputFileST) {
+	public void writeBaseListener(ST outputFileST) {
-		target.genFile(g,outputFileST, getBlankListenerFileName());
+		target.genFile(g,outputFileST, getBaseListenerFileName());
 	}
 
 	public void writeVisitor(ST outputFileST) {
 		target.genFile(g,outputFileST, getVisitorFileName());
 	}
 
+	public void writeBaseVisitor(ST outputFileST) {
+		target.genFile(g,outputFileST, getBaseVisitorFileName());
+	}
+
 	public void writeHeaderFile() {
 		String fileName = getHeaderFileName();
 		if ( fileName==null ) return;
@@ -333,15 +350,25 @@ public class CodeGenerator {
 	}
 
 	/** A given grammar T, return a blank listener implementation
-	 *  such as BlankTListener.java, if we're using the Java target.
+	 *  such as TBaseListener.java, if we're using the Java target.
  	 */
-	public String getBlankListenerFileName() {
+	public String getBaseListenerFileName() {
 		assert g.name != null;
 		ST extST = templates.getInstanceOf("codeFileExtension");
 		String listenerName = g.name + "BaseListener";
 		return listenerName+extST.render();
 	}
 
+	/** A given grammar T, return a blank listener implementation
+	 *  such as TBaseListener.java, if we're using the Java target.
+ 	 */
+	public String getBaseVisitorFileName() {
+		assert g.name != null;
+		ST extST = templates.getInstanceOf("codeFileExtension");
+		String listenerName = g.name + "BaseVisitor";
+		return listenerName+extST.render();
+	}
+
 	/** What is the name of the vocab file generated for this grammar?
 	 *  Returns null if no .tokens file should be generated.
 	 */

tool/src/org/antlr/v4/codegen/OutputModelController.java

@@ -108,9 +108,9 @@ public class OutputModelController {
 		return new ListenerFile(delegate, gen.getListenerFileName());
 	}
 
-	public OutputModelObject buildBlankListenerOutputModel() {
+	public OutputModelObject buildBaseListenerOutputModel() {
 		CodeGenerator gen = delegate.getGenerator();
-		return new BaseListenerFile(delegate, gen.getBlankListenerFileName());
+		return new BaseListenerFile(delegate, gen.getBaseListenerFileName());
 	}
 
 	public OutputModelObject buildVisitorOutputModel() {
@@ -118,6 +118,11 @@ public class OutputModelController {
 		return new VisitorFile(delegate, gen.getVisitorFileName());
 	}
 
+	public OutputModelObject buildBaseVisitorOutputModel() {
+		CodeGenerator gen = delegate.getGenerator();
+		return new BaseVisitorFile(delegate, gen.getBaseVisitorFileName());
+	}
+
 	public ParserFile parserFile(String fileName) {
 		ParserFile f = delegate.parserFile(fileName);
 		for (CodeGeneratorExtension ext : extensions) f = ext.parserFile(f);

tool/src/org/antlr/v4/codegen/model/BaseVisitorFile.java

@@ -0,0 +1,9 @@
+package org.antlr.v4.codegen.model;
+
+import org.antlr.v4.codegen.OutputModelFactory;
+
+public class BaseVisitorFile extends VisitorFile {
+	public BaseVisitorFile(OutputModelFactory factory, String fileName) {
+		super(factory, fileName);
+	}
+}

tool/src/org/antlr/v4/codegen/model/ListenerFile.java

@@ -14,7 +14,6 @@ public class ListenerFile extends OutputFile {
 	public String grammarName;
 	public String parserName;
 	public Set<String> listenerNames = new HashSet<String>();
-//	public List<String> ruleNames = new ArrayList<String>();
 
 	@ModelElement public Action header;