From bf194654373d42d1200e337312cf825403a721a0 Mon Sep 17 00:00:00 2001
From: parrt <parrt@antlr.org>
Date: Fri, 9 Sep 2011 17:08:13 -0800
Subject: [PATCH] Got a rule labels added to the tree and also altered code
 generation so that it pays attention to the labels. fairly major surgery but
 it's a nice refactoring.

[git-p4: depot-paths = "//depot/code/antlr4/main/": change = 9062]
---
 .../antlr/v4/runtime/ParserRuleContext.java   |  2 +-
 tool/playground/T.g                           |  6 ++-
 .../v4/tool/templates/codegen/Java/Java.stg   | 37 ++++++++++++++-----
 .../v4/codegen/BlankOutputModelFactory.java   |  2 +-
 .../v4/codegen/OutputModelController.java     |  2 +-
 .../antlr/v4/codegen/OutputModelFactory.java  |  2 +-
 .../org/antlr/v4/codegen/ParserFactory.java   |  9 ++++-
 .../model/CodeBlockForOuterMostAlt.java       | 16 ++++++++
 .../antlr/v4/codegen/model/ListenerFile.java  | 20 ++++++++--
 .../antlr/v4/codegen/model/RuleFunction.java  | 11 ++++--
 .../model/SwitchedVisitorDispatchMethod.java  | 23 ++++++++++++
 .../codegen/model/VisitorDispatchMethod.java  | 18 +++++++++
 .../v4/codegen/model/decl/StructDecl.java     | 23 +++++++++---
 tool/src/org/antlr/v4/misc/CharSupport.java   |  3 ++
 tool/src/org/antlr/v4/parse/ANTLRLexer.g      |  1 +
 tool/src/org/antlr/v4/parse/ANTLRParser.g     | 19 +++++++---
 .../antlr/v4/semantics/AttributeChecks.java   |  8 ++--
 .../v4/semantics/BasicSemanticChecks.java     |  4 +-
 tool/src/org/antlr/v4/tool/AltAST.java        |  7 +++-
 tool/src/org/antlr/v4/tool/Alternative.java   | 12 +++---
 tool/src/org/antlr/v4/tool/Rule.java          | 21 ++++++++---
 21 files changed, 197 insertions(+), 49 deletions(-)
 create mode 100644 tool/src/org/antlr/v4/codegen/model/CodeBlockForOuterMostAlt.java
 create mode 100644 tool/src/org/antlr/v4/codegen/model/SwitchedVisitorDispatchMethod.java
 create mode 100644 tool/src/org/antlr/v4/codegen/model/VisitorDispatchMethod.java

diff --git a/runtime/Java/src/org/antlr/v4/runtime/ParserRuleContext.java b/runtime/Java/src/org/antlr/v4/runtime/ParserRuleContext.java
index 3837d857d..8573f1cd9 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/ParserRuleContext.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/ParserRuleContext.java
@@ -57,7 +57,7 @@ public class ParserRuleContext extends RuleContext {
 	public int ruleIndex;
 
 	/** Set during parsing to identify which alt of rule parser is in. */
-	public int alt;
+	public int altNum;
 
 	public ParserRuleContext() { super(); }
 
diff --git a/tool/playground/T.g b/tool/playground/T.g
index 8d7c4cd68..2d79111f3 100644
--- a/tool/playground/T.g
+++ b/tool/playground/T.g
@@ -1,10 +1,12 @@
 grammar T;
 s : i=ifstat  {System.out.println(_input.toString(0,_input.index()-1));} ;
-ifstat : 'if' '(' INT ')' ID '=' ID ';' ;
+
+ifstat : 'if' '(' INT ')' ID '=' ID ';' # DoIf;
 
 r[int x] returns [int y]
 locals [int z]
-	: name=ID
+	: name=ID		# foo
+	| ID (ID|';'{;})	# bar
 	;
 
 EQ : '=' ;
diff --git a/tool/resources/org/antlr/v4/tool/templates/codegen/Java/Java.stg b/tool/resources/org/antlr/v4/tool/templates/codegen/Java/Java.stg
index 9227398ad..051bb8ab8 100644
--- a/tool/resources/org/antlr/v4/tool/templates/codegen/Java/Java.stg
+++ b/tool/resources/org/antlr/v4/tool/templates/codegen/Java/Java.stg
@@ -41,9 +41,9 @@ import org.antlr.v4.runtime.tree.ParseTreeListener;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused"})
 public interface <listener.grammarName>Listener extends ParseTreeListener {
-    <listener.rules:{r |
-void enterRule(<listener.parserName>.<r.name>Context ctx);
-void exitRule(<listener.parserName>.<r.name>Context ctx);}; separator="\n">
+    <listener.listenerNames,listener.ruleNames:{lname,rname |
+void enter<lname>(<listener.parserName>.<rname>Context ctx);
+void exit<lname>(<listener.parserName>.<rname>Context ctx);}; separator="\n">
 }
 >>
 
@@ -55,9 +55,9 @@ import org.antlr.v4.runtime.Token;
 
 @SuppressWarnings({"all", "warnings", "unchecked", "unused"})
 public class Blank<listener.grammarName>Listener implements <listener.grammarName>Listener {
-    <listener.rules:{r |
-public void enterRule(<listener.parserName>.<r.name>Context ctx) { \}
-public void exitRule(<listener.parserName>.<r.name>Context ctx) { \}}; separator="\n">
+    <listener.listenerNames,listener.ruleNames:{lname,rname |
+public void enter<lname>(<listener.parserName>.<rname>Context ctx) { \}
+public void exit<lname>(<listener.parserName>.<rname>Context ctx) { \}}; separator="\n">
 
 	public void enterEveryRule(ParserRuleContext ctx) { }
 	public void exitEveryRule(ParserRuleContext ctx) { }
@@ -188,6 +188,11 @@ public QStack\<<currentRule.ctxType>\> <currentRule.name>_stk = new QStack\<<cur
 }
 >>
 
+CodeBlockForOuterMostAlt(c, locals, preamble, ops) ::= <<
+_ctx.altNum = <c.altNum>;
+<CodeBlockForAlt(...)>
+>>
+
 CodeBlockForAlt(c, locals, preamble, ops) ::= <<
 {
 <locals; separator="\n">
@@ -442,7 +447,7 @@ ListLabelName(label)		  ::= "<label>_list"
 CaptureNextToken(d) ::= "<d.varName> = _input.LT(1);"
 CaptureNextTokenType(d) ::= "<d.varName> = _input.LA(1);"
 
-StructDecl(s,attrs) ::= <<
+StructDecl(s,attrs,visitorDispatchMethods) ::= <<
 public static class <s.name> extends ParserRuleContext {
     <attrs:{a | public <a>;}; separator="\n">
     <if(s.ctorAttrs)>public <s.name>(RuleContext parent, int state) { super(parent, state); }<endif>
@@ -450,8 +455,22 @@ public static class <s.name> extends ParserRuleContext {
     	super(parent, state);
         <s.ctorAttrs:{a | this.<a.name> = <a.name>;}; separator="\n">
     }
-	public void enterRule(ParseTreeListener listener) { ((<parser.grammarName>Listener)listener).enterRule(this); }
-	public void exitRule(ParseTreeListener listener) { ((<parser.grammarName>Listener)listener).exitRule(this); }
+    <visitorDispatchMethods; separator="\n">
+}
+>>
+
+VisitorDispatchMethod(method) ::= <<
+public void <if(method.isEnter)>enter<else>exit<endif>Rule(ParseTreeListener listener) {
+    ((<parser.grammarName>Listener)listener).<if(method.isEnter)>enter<else>exit<endif><method.listenerName>(this);
+}
+>>
+
+SwitchedVisitorDispatchMethod(method) ::= <<
+public void <if(method.isEnter)>enter<else>exit<endif>Rule(ParseTreeListener listener) {
+    switch ( altNum ) {
+        <method.listenerNames:{m |
+case <i> : ((<parser.grammarName>Listener)listener).<if(method.isEnter)>enter<else>exit<endif><m>(this); break;}; separator="\n">
+    }
 }
 >>
 
diff --git a/tool/src/org/antlr/v4/codegen/BlankOutputModelFactory.java b/tool/src/org/antlr/v4/codegen/BlankOutputModelFactory.java
index e37ca11c6..7c295c7bc 100644
--- a/tool/src/org/antlr/v4/codegen/BlankOutputModelFactory.java
+++ b/tool/src/org/antlr/v4/codegen/BlankOutputModelFactory.java
@@ -51,7 +51,7 @@ public abstract class BlankOutputModelFactory implements OutputModelFactory {
 
 	// ALTERNATIVES / ELEMENTS
 
-	public CodeBlockForAlt alternative(Alternative alt) { return null; }
+	public CodeBlockForAlt alternative(Alternative alt, boolean outerMost) { return null; }
 
 	public CodeBlockForAlt finishAlternative(CodeBlockForAlt blk, List<SrcOp> ops) { return blk; }
 
diff --git a/tool/src/org/antlr/v4/codegen/OutputModelController.java b/tool/src/org/antlr/v4/codegen/OutputModelController.java
index afde14393..cca6be643 100644
--- a/tool/src/org/antlr/v4/codegen/OutputModelController.java
+++ b/tool/src/org/antlr/v4/codegen/OutputModelController.java
@@ -238,7 +238,7 @@ public class OutputModelController {
 	public CodeGenerator getGenerator() { return delegate.getGenerator(); }
 
 	public CodeBlockForAlt alternative(Alternative alt, boolean outerMost) {
-		CodeBlockForAlt blk = delegate.alternative(alt);
+		CodeBlockForAlt blk = delegate.alternative(alt, outerMost);
 		if ( outerMost ) currentOuterMostAlternativeBlock = blk;
 		for (CodeGeneratorExtension ext : extensions) blk = ext.alternative(blk, outerMost);
 		return blk;
diff --git a/tool/src/org/antlr/v4/codegen/OutputModelFactory.java b/tool/src/org/antlr/v4/codegen/OutputModelFactory.java
index fb8fb4e5f..928979428 100644
--- a/tool/src/org/antlr/v4/codegen/OutputModelFactory.java
+++ b/tool/src/org/antlr/v4/codegen/OutputModelFactory.java
@@ -58,7 +58,7 @@ public interface OutputModelFactory {
 
 	// ELEMENT TRIGGERS
 
-	CodeBlockForAlt alternative(Alternative alt);
+	CodeBlockForAlt alternative(Alternative alt, boolean outerMost);
 
 	CodeBlockForAlt finishAlternative(CodeBlockForAlt blk, List<SrcOp> ops);
 
diff --git a/tool/src/org/antlr/v4/codegen/ParserFactory.java b/tool/src/org/antlr/v4/codegen/ParserFactory.java
index 5ff9c2181..03b4ed965 100644
--- a/tool/src/org/antlr/v4/codegen/ParserFactory.java
+++ b/tool/src/org/antlr/v4/codegen/ParserFactory.java
@@ -34,7 +34,9 @@ import org.antlr.v4.codegen.model.*;
 import org.antlr.v4.codegen.model.ast.*;
 import org.antlr.v4.codegen.model.decl.*;
 import org.antlr.v4.parse.ANTLRParser;
-import org.antlr.v4.runtime.atn.*;
+import org.antlr.v4.runtime.atn.DecisionState;
+import org.antlr.v4.runtime.atn.PlusBlockStartState;
+import org.antlr.v4.runtime.atn.StarLoopEntryState;
 import org.antlr.v4.runtime.misc.IntervalSet;
 import org.antlr.v4.semantics.UseDefAnalyzer;
 import org.antlr.v4.tool.*;
@@ -59,7 +61,10 @@ public class ParserFactory extends DefaultOutputModelFactory {
 
 	public CodeBlockForAlt epsilon() { return new CodeBlockForAlt(this); }
 
-	public CodeBlockForAlt alternative(Alternative alt) { return new CodeBlockForAlt(this); }
+	public CodeBlockForAlt alternative(Alternative alt, boolean outerMost) {
+		if ( outerMost ) return new CodeBlockForOuterMostAlt(this, alt.altNum);
+		return new CodeBlockForAlt(this);
+	}
 
 	@Override
 	public CodeBlockForAlt finishAlternative(CodeBlockForAlt blk, List<SrcOp> ops) {
diff --git a/tool/src/org/antlr/v4/codegen/model/CodeBlockForOuterMostAlt.java b/tool/src/org/antlr/v4/codegen/model/CodeBlockForOuterMostAlt.java
new file mode 100644
index 000000000..984364eb2
--- /dev/null
+++ b/tool/src/org/antlr/v4/codegen/model/CodeBlockForOuterMostAlt.java
@@ -0,0 +1,16 @@
+package org.antlr.v4.codegen.model;
+
+import org.antlr.v4.codegen.OutputModelFactory;
+
+/** The code associated with an outermost alternative overrule.
+ *  Sometimes we might want to treat them differently in the
+ *  code generation.
+ */
+public class CodeBlockForOuterMostAlt extends CodeBlockForAlt {
+	public int altNum;
+
+	public CodeBlockForOuterMostAlt(OutputModelFactory factory, int altNum) {
+		super(factory);
+		this.altNum = altNum;
+	}
+}
diff --git a/tool/src/org/antlr/v4/codegen/model/ListenerFile.java b/tool/src/org/antlr/v4/codegen/model/ListenerFile.java
index 6ae631c63..8e6609857 100644
--- a/tool/src/org/antlr/v4/codegen/model/ListenerFile.java
+++ b/tool/src/org/antlr/v4/codegen/model/ListenerFile.java
@@ -1,11 +1,13 @@
 package org.antlr.v4.codegen.model;
 
 import org.antlr.v4.codegen.OutputModelFactory;
+import org.antlr.v4.misc.CharSupport;
 import org.antlr.v4.tool.ActionAST;
 import org.antlr.v4.tool.Grammar;
 import org.antlr.v4.tool.Rule;
 
-import java.util.Collection;
+import java.util.ArrayList;
+import java.util.List;
 
 /** A model object representing a parse tree listener file.
  *  These are the rules specific events triggered by a parse tree visitor.
@@ -14,7 +16,8 @@ public class ListenerFile extends OutputModelObject {
 	public String fileName;
 	public String grammarName;
 	public String parserName;
-	public Collection<Rule> rules;
+	public List<String> listenerNames = new ArrayList<String>();
+	public List<String> ruleNames = new ArrayList<String>();
 
 	@ModelElement public Action header;
 
@@ -24,7 +27,18 @@ public class ListenerFile extends OutputModelObject {
 		Grammar g = factory.getGrammar();
 		parserName = g.getRecognizerName();
 		grammarName = g.name;
-		rules = g.rules.values();
+		for (Rule r : g.rules.values()) {
+			List<String> labels = r.getAltLabels();
+			if ( labels==null ) {
+				listenerNames.add("Rule"); ruleNames.add(r.name);
+			}
+			else { // alt(s) with label(s)
+				for (String label : labels) {
+					String labelCapitalized = CharSupport.capitalize(label);
+					listenerNames.add(labelCapitalized); ruleNames.add(r.name);
+				}
+			}
+		}
 		ActionAST ast = g.namedActions.get("header");
 		if ( ast!=null ) header = new Action(factory, ast);
 	}
diff --git a/tool/src/org/antlr/v4/codegen/model/RuleFunction.java b/tool/src/org/antlr/v4/codegen/model/RuleFunction.java
index 19bdcbed9..92baf7778 100644
--- a/tool/src/org/antlr/v4/codegen/model/RuleFunction.java
+++ b/tool/src/org/antlr/v4/codegen/model/RuleFunction.java
@@ -30,11 +30,14 @@
 package org.antlr.v4.codegen.model;
 
 import org.antlr.v4.codegen.OutputModelFactory;
-import org.antlr.v4.codegen.model.decl.*;
+import org.antlr.v4.codegen.model.decl.Decl;
+import org.antlr.v4.codegen.model.decl.StructDecl;
 import org.antlr.v4.misc.Utils;
 import org.antlr.v4.runtime.atn.ATNState;
 import org.antlr.v4.runtime.misc.OrderedHashSet;
-import org.antlr.v4.tool.*;
+import org.antlr.v4.tool.Attribute;
+import org.antlr.v4.tool.GrammarAST;
+import org.antlr.v4.tool.Rule;
 
 import java.util.*;
 
@@ -72,7 +75,7 @@ public class RuleFunction extends OutputModelObject {
 		index = r.index;
 
 		// might need struct; build but drop later if no elements
-		ruleCtx = new StructDecl(factory);
+		ruleCtx = new StructDecl(factory, r);
 
 		if ( r.args!=null ) {
 			ruleCtx.addDecls(r.args.attributes.values());
@@ -86,7 +89,7 @@ public class RuleFunction extends OutputModelObject {
 			ruleCtx.addDecls(r.scope.attributes.values());
 		}
 
-		ruleLabels = r.getLabelNames();
+		ruleLabels = r.getElementLabelNames();
 		tokenLabels = r.getTokenRefs();
 		exceptions = Utils.nodesToStrings(r.exceptionActions);
 		if ( r.finallyAction!=null ) finallyAction = new Action(factory, r.finallyAction);
diff --git a/tool/src/org/antlr/v4/codegen/model/SwitchedVisitorDispatchMethod.java b/tool/src/org/antlr/v4/codegen/model/SwitchedVisitorDispatchMethod.java
new file mode 100644
index 000000000..857b9a80e
--- /dev/null
+++ b/tool/src/org/antlr/v4/codegen/model/SwitchedVisitorDispatchMethod.java
@@ -0,0 +1,23 @@
+package org.antlr.v4.codegen.model;
+
+import org.antlr.v4.codegen.OutputModelFactory;
+import org.antlr.v4.misc.CharSupport;
+import org.antlr.v4.tool.Rule;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class SwitchedVisitorDispatchMethod extends VisitorDispatchMethod {
+	public List<String> listenerNames = new ArrayList<String>();
+
+	public SwitchedVisitorDispatchMethod(OutputModelFactory factory, Rule r, boolean isEnter) {
+		super(factory, r, isEnter);
+		RuleFunction rf = factory.getCurrentRuleFunction();
+		this.isEnter = isEnter;
+		List<String> labels = r.getAltLabels();
+		for (String label : labels) {
+			String labelCapitalized = CharSupport.capitalize(label);
+			listenerNames.add(labelCapitalized);
+		}
+	}
+}
diff --git a/tool/src/org/antlr/v4/codegen/model/VisitorDispatchMethod.java b/tool/src/org/antlr/v4/codegen/model/VisitorDispatchMethod.java
new file mode 100644
index 000000000..65d23a6d8
--- /dev/null
+++ b/tool/src/org/antlr/v4/codegen/model/VisitorDispatchMethod.java
@@ -0,0 +1,18 @@
+package org.antlr.v4.codegen.model;
+
+import org.antlr.v4.codegen.OutputModelFactory;
+import org.antlr.v4.tool.Rule;
+
+import java.util.List;
+
+public class VisitorDispatchMethod extends OutputModelObject {
+	public String listenerName = "Rule";
+	public boolean isEnter;
+
+	public VisitorDispatchMethod(OutputModelFactory factory, Rule r, boolean isEnter) {
+		super(factory);
+		this.isEnter = isEnter;
+		List<String> label = r.getAltLabels();
+		if ( label!=null ) listenerName = label.get(0);
+	}
+}
diff --git a/tool/src/org/antlr/v4/codegen/model/decl/StructDecl.java b/tool/src/org/antlr/v4/codegen/model/decl/StructDecl.java
index 7ad6ef789..deea7d72a 100644
--- a/tool/src/org/antlr/v4/codegen/model/decl/StructDecl.java
+++ b/tool/src/org/antlr/v4/codegen/model/decl/StructDecl.java
@@ -31,22 +31,35 @@ package org.antlr.v4.codegen.model.decl;
 
 import org.antlr.v4.codegen.OutputModelFactory;
 import org.antlr.v4.codegen.model.ModelElement;
+import org.antlr.v4.codegen.model.SwitchedVisitorDispatchMethod;
+import org.antlr.v4.codegen.model.VisitorDispatchMethod;
 import org.antlr.v4.runtime.misc.OrderedHashSet;
 import org.antlr.v4.tool.Attribute;
+import org.antlr.v4.tool.Rule;
 
+import java.util.ArrayList;
 import java.util.Collection;
+import java.util.List;
 
 /** */
 public class StructDecl extends Decl {
 	@ModelElement public OrderedHashSet<Decl> attrs = new OrderedHashSet<Decl>();
 	@ModelElement public Collection<Attribute> ctorAttrs;
+	@ModelElement public List<VisitorDispatchMethod> visitorDispatchMethods;
 
-	public StructDecl(OutputModelFactory factory) {
+	public StructDecl(OutputModelFactory factory, Rule r) {
 		super(factory, null);
-	}
-
-	public StructDecl(OutputModelFactory factory, String name) {
-		super(factory, name);
+		List<String> labels = r.getAltLabels();
+		boolean multiAlts = labels!=null && labels.size()>1;
+		visitorDispatchMethods = new ArrayList<VisitorDispatchMethod>();
+		VisitorDispatchMethod enter = multiAlts ?
+			new SwitchedVisitorDispatchMethod(factory, r, true) :
+			new VisitorDispatchMethod(factory, r, true);
+		visitorDispatchMethods.add(enter);
+		VisitorDispatchMethod exit = multiAlts ?
+			new SwitchedVisitorDispatchMethod(factory, r, false) :
+			new VisitorDispatchMethod(factory, r, false);
+		visitorDispatchMethods.add(exit);
 	}
 
 	public void addDecl(Decl d) { attrs.add(d); }
diff --git a/tool/src/org/antlr/v4/misc/CharSupport.java b/tool/src/org/antlr/v4/misc/CharSupport.java
index 0ab744b70..4da03fcaf 100644
--- a/tool/src/org/antlr/v4/misc/CharSupport.java
+++ b/tool/src/org/antlr/v4/misc/CharSupport.java
@@ -157,4 +157,7 @@ public class CharSupport {
 		return buf.toString();
 	}
 
+	public static final String capitalize(String s) {
+		return Character.toUpperCase(s.charAt(0)) + s.substring(1);
+	}
 }
diff --git a/tool/src/org/antlr/v4/parse/ANTLRLexer.g b/tool/src/org/antlr/v4/parse/ANTLRLexer.g
index c9b4919b7..f0cff348c 100644
--- a/tool/src/org/antlr/v4/parse/ANTLRLexer.g
+++ b/tool/src/org/antlr/v4/parse/ANTLRLexer.g
@@ -448,6 +448,7 @@ ETC          : '...'                  ;
 RARROW       : '->'                   ;
 TREE_BEGIN   : '^('                   ;
 AT           : '@'                    ;
+POUND        : '#'                    ;
 NOT          : '~'                    ;
 RBRACE       : '}'                    ;
 
diff --git a/tool/src/org/antlr/v4/parse/ANTLRParser.g b/tool/src/org/antlr/v4/parse/ANTLRParser.g
index 2b3418f59..947dc717b 100644
--- a/tool/src/org/antlr/v4/parse/ANTLRParser.g
+++ b/tool/src/org/antlr/v4/parse/ANTLRParser.g
@@ -530,10 +530,6 @@ ruleModifier
     | FRAGMENT
     ;
 
-altList
-    : alternative (OR alternative)* -> alternative+
-    ;
-
 // A set of alts, rewritten as a BLOCK for generic processing
 // in tree walkers. Used by the rule 'rule' so that the list of
 // alts for a rule appears as a BLOCK containing the alts and
@@ -542,13 +538,26 @@ altList
 // boundaries set correctly by rule post processing of rewrites.
 ruleBlock
 @init {Token colon = input.LT(-1);}
-    : altList -> ^(BLOCK<BlockAST>[colon,"BLOCK"] altList)
+    :	ruleAltList -> ^(BLOCK<BlockAST>[colon,"BLOCK"] ruleAltList)
     ;
     catch [ResyncToEndOfRuleBlock e] {
     	// just resyncing; ignore error
 		retval.tree = (GrammarAST)adaptor.errorNode(input, retval.start, input.LT(-1), null);
     }
 
+ruleAltList
+	:	labeledAlt (OR labeledAlt)* -> labeledAlt+
+	;
+	
+labeledAlt
+	:	alternative (POUND id {((AltAST)$alternative.tree).altLabel=$id.tree;})?
+		-> alternative
+	;
+	
+altList
+    :	alternative (OR alternative)* -> alternative+
+    ;
+
 // An individual alt with an optional rewrite clause for the
 // elements of the alt.
 alternative
diff --git a/tool/src/org/antlr/v4/semantics/AttributeChecks.java b/tool/src/org/antlr/v4/semantics/AttributeChecks.java
index 78151efed..97d21d309 100644
--- a/tool/src/org/antlr/v4/semantics/AttributeChecks.java
+++ b/tool/src/org/antlr/v4/semantics/AttributeChecks.java
@@ -29,8 +29,10 @@
 
 package org.antlr.v4.semantics;
 
-import org.antlr.runtime.*;
-import org.antlr.v4.parse.*;
+import org.antlr.runtime.ANTLRStringStream;
+import org.antlr.runtime.Token;
+import org.antlr.v4.parse.ActionSplitter;
+import org.antlr.v4.parse.ActionSplitterListener;
 import org.antlr.v4.tool.*;
 
 import java.util.List;
@@ -204,7 +206,7 @@ public class AttributeChecks implements ActionSplitterListener {
 		if ( x.equals(r.name) ) return r;
 		List<LabelElementPair> labels = null;
 		if ( node.resolver instanceof Rule ) {
-			labels = r.getLabelDefs().get(x);
+			labels = r.getElementLabelDefs().get(x);
 		}
 		else if ( node.resolver instanceof Alternative ) {
 			labels = ((Alternative)node.resolver).labelDefs.get(x);
diff --git a/tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java b/tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java
index 721e07f45..6889e28a3 100644
--- a/tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java
+++ b/tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java
@@ -31,7 +31,8 @@ package org.antlr.v4.semantics;
 
 import org.antlr.runtime.Token;
 import org.antlr.v4.misc.Utils;
-import org.antlr.v4.parse.*;
+import org.antlr.v4.parse.ANTLRParser;
+import org.antlr.v4.parse.GrammarTreeVisitor;
 import org.antlr.v4.tool.*;
 import org.stringtemplate.v4.misc.MultiMap;
 
@@ -205,6 +206,7 @@ public class BasicSemanticChecks extends GrammarTreeVisitor {
 							 GrammarAST thrws, GrammarAST options,
 							 List<GrammarAST> actions, GrammarAST block)
 	{
+		// TODO: chk that all or no alts have "# label"
 		checkInvalidRuleDef(ID.token);
 	}
 
diff --git a/tool/src/org/antlr/v4/tool/AltAST.java b/tool/src/org/antlr/v4/tool/AltAST.java
index 05cc2bd67..6940c4a9f 100644
--- a/tool/src/org/antlr/v4/tool/AltAST.java
+++ b/tool/src/org/antlr/v4/tool/AltAST.java
@@ -33,10 +33,15 @@ import org.antlr.runtime.Token;
 import org.antlr.runtime.tree.Tree;
 import org.antlr.v4.parse.ANTLRParser;
 
-/** An ALT (which can be child of ALT_REWRITE node) */
+/** Any ALT (which can be child of ALT_REWRITE node) */
 public class AltAST extends GrammarAST {
 	public Alternative alt;
 
+	/** If someone specified an outermost alternative label with #foo.
+	 *  Token type will be ID.
+	 */
+	public GrammarAST altLabel;
+
 	public AltAST(GrammarAST node) {
 		super(node);
 		this.alt = ((AltAST)node).alt;
diff --git a/tool/src/org/antlr/v4/tool/Alternative.java b/tool/src/org/antlr/v4/tool/Alternative.java
index 394b906d5..a228b6d61 100644
--- a/tool/src/org/antlr/v4/tool/Alternative.java
+++ b/tool/src/org/antlr/v4/tool/Alternative.java
@@ -33,16 +33,18 @@ package org.antlr.v4.tool;
 import org.antlr.v4.parse.ANTLRParser;
 import org.stringtemplate.v4.misc.MultiMap;
 
-import java.util.*;
+import java.util.ArrayList;
+import java.util.List;
 
-/** Record use/def information about an outermost alternative in a subrule
- *  or rule of a grammar.
- */
+/** An outermost alternative for a rule.  We don't track inner alternatives. */
 public class Alternative implements AttributeResolver {
     public Rule rule;
 
 	public AltAST ast;
 
+	/** What alternative number is this outermost alt? 1..n */
+	public int altNum;
+
     // token IDs, string literals in this alt
     public MultiMap<String, TerminalAST> tokenRefs = new MultiMap<String, TerminalAST>();
 
@@ -70,7 +72,7 @@ public class Alternative implements AttributeResolver {
      */
     public List<ActionAST> actions = new ArrayList<ActionAST>();
 
-    public Alternative(Rule r) { this.rule = r; }
+    public Alternative(Rule r, int altNum) { this.rule = r; this.altNum = altNum; }
 
 	/** (ALT_REWRITE (ALT ...) (-> (ALT ...))); rewrite might nested in subrule */
 	public boolean hasRewrite() {
diff --git a/tool/src/org/antlr/v4/tool/Rule.java b/tool/src/org/antlr/v4/tool/Rule.java
index be0d29d08..a289d227e 100644
--- a/tool/src/org/antlr/v4/tool/Rule.java
+++ b/tool/src/org/antlr/v4/tool/Rule.java
@@ -124,7 +124,7 @@ public class Rule implements AttributeResolver {
 		this.ast = ast;
 		this.numberOfAlts = numberOfAlts;
 		alt = new Alternative[numberOfAlts+1]; // 1..n
-		for (int i=1; i<=numberOfAlts; i++) alt[i] = new Alternative(this);
+		for (int i=1; i<=numberOfAlts; i++) alt[i] = new Alternative(this, i);
 	}
 
 	public void defineActionInAlt(int currentAlt, ActionAST actionAST) {
@@ -163,7 +163,7 @@ public class Rule implements AttributeResolver {
 		return refs;
     }
 
-    public Set<String> getLabelNames() {
+    public Set<String> getElementLabelNames() {
         Set<String> refs = new HashSet<String>();
         for (int i=1; i<=numberOfAlts; i++) {
             refs.addAll(alt[i].labelDefs.keySet());
@@ -172,7 +172,7 @@ public class Rule implements AttributeResolver {
         return refs;
     }
 
-    public MultiMap<String, LabelElementPair> getLabelDefs() {
+    public MultiMap<String, LabelElementPair> getElementLabelDefs() {
         MultiMap<String, LabelElementPair> defs =
             new MultiMap<String, LabelElementPair>();
         for (int i=1; i<=numberOfAlts; i++) {
@@ -185,7 +185,18 @@ public class Rule implements AttributeResolver {
         return defs;
     }
 
-		/**  $x		Attribute: rule arguments, return values, predefined rule prop.
+	public List<String> getAltLabels() {
+		List<String> labels = new ArrayList<String>();
+		for (int i=1; i<=numberOfAlts; i++) {
+			GrammarAST altLabel = alt[i].ast.altLabel;
+			if ( altLabel==null ) break; // all or none
+			labels.add(altLabel.getText());
+		}
+		if ( labels.size()==0 ) return null;
+		return labels;
+	}
+
+	/**  $x		Attribute: rule arguments, return values, predefined rule prop.
 	 */
 	public Attribute resolveToAttribute(String x, ActionAST node) {
 		if ( args!=null ) {
@@ -253,7 +264,7 @@ public class Rule implements AttributeResolver {
 	}
 
 	public LabelElementPair getAnyLabelDef(String x) {
-		List<LabelElementPair> labels = getLabelDefs().get(x);
+		List<LabelElementPair> labels = getElementLabelDefs().get(x);
 		if ( labels!=null ) return labels.get(0);
 		return null;
 	}