From 19f861ee8117826f09d2a2d2f69246582e14bea9 Mon Sep 17 00:00:00 2001
From: Sam Harwell <sam@tunnelvisionlabs.com>
Date: Thu, 10 Jan 2013 14:46:52 -0600
Subject: [PATCH] Added error message 135: cannot assign a value to list label:
 $label

---
 tool/src/org/antlr/v4/semantics/AttributeChecks.java | 8 +++++++-
 tool/src/org/antlr/v4/tool/ErrorType.java            | 1 +
 tool/test/org/antlr/v4/test/TestAttributeChecks.java | 1 +
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/tool/src/org/antlr/v4/semantics/AttributeChecks.java b/tool/src/org/antlr/v4/semantics/AttributeChecks.java
index 7335c8839..94c48ea45 100644
--- a/tool/src/org/antlr/v4/semantics/AttributeChecks.java
+++ b/tool/src/org/antlr/v4/semantics/AttributeChecks.java
@@ -161,7 +161,13 @@ public class AttributeChecks implements ActionSplitterListener {
 			return;
 		}
 		if ( node.resolver.resolveToAttribute(x.getText(), node)==null ) {
-			errMgr.grammarError(ErrorType.UNKNOWN_SIMPLE_ATTRIBUTE,
+			ErrorType errorType = ErrorType.UNKNOWN_SIMPLE_ATTRIBUTE;
+			if ( node.resolver.resolvesToListLabel(x.getText(), node) ) {
+				// $ids for ids+=ID etc...
+				errorType = ErrorType.ASSIGNMENT_TO_LIST_LABEL;
+			}
+
+			errMgr.grammarError(errorType,
 								g.fileName, x, x.getText(), expr);
 		}
 		new AttributeChecks(g, r, alt, node, rhs).examineAction();
diff --git a/tool/src/org/antlr/v4/tool/ErrorType.java b/tool/src/org/antlr/v4/tool/ErrorType.java
index ce0bb066a..42896ef5d 100644
--- a/tool/src/org/antlr/v4/tool/ErrorType.java
+++ b/tool/src/org/antlr/v4/tool/ErrorType.java
@@ -115,6 +115,7 @@ public enum ErrorType {
 	LEXER_COMMAND_PLACEMENT_ISSUE(133, "->command in lexer rule <arg> must be last element of single outermost alt", ErrorSeverity.ERROR),
 	USE_OF_BAD_WORD(134, "symbol <arg> conflicts with generated code in target language or runtime", ErrorSeverity.ERROR),
 	INVALID_LEXER_SET_ELEMENT(134, "lexer set element <arg> is invalid (either lexer rule ref or literal with > 1 char)", ErrorSeverity.ERROR),
+	ASSIGNMENT_TO_LIST_LABEL(135, "cannot assign a value to list label: $<arg>", ErrorSeverity.ERROR),
 
 	// Backward incompatibility errors
 	V3_TREE_GRAMMAR(200, "tree grammars are not supported in ANTLR 4", ErrorSeverity.ERROR),
diff --git a/tool/test/org/antlr/v4/test/TestAttributeChecks.java b/tool/test/org/antlr/v4/test/TestAttributeChecks.java
index 6ea490de0..95c03f806 100644
--- a/tool/test/org/antlr/v4/test/TestAttributeChecks.java
+++ b/tool/test/org/antlr/v4/test/TestAttributeChecks.java
@@ -102,6 +102,7 @@ public class TestAttributeChecks extends BaseTest {
 		"$b.d",         "error(64): A.g4:7:6: cannot access rule d's parameter: $b.d\n",  // can't see rule ref's arg
 		"$d.text",      "error(63): A.g4:7:4: unknown attribute reference d in $d.text\n", // valid rule, but no ref
 		"$lab.d",		"error(64): A.g4:7:8: cannot access rule d's parameter: $lab.d\n",
+		"$ids = null;",	"error(135): A.g4:7:4: cannot assign a value to list label: $ids\n",
 	};
 
 	String[] finallyChecks = {