Do not require escape for $ in action when not followed by an ID start char (fixes #176)

tool/src/org/antlr/v4/parse/ActionSplitter.g

@@ -56,6 +56,10 @@ public List<Token> getActionTokens() {
     }
     return chunks;
 }
+
+private boolean isIDStartChar(int c) {
+	return c == '_' || Character.isLetter(c);
+}
 }
 
 // ignore comments right away
@@ -106,8 +110,9 @@ TEXT
 @init {StringBuilder buf = new StringBuilder();}
 @after {delegate.text(buf.toString());}
 	:	(	c=~('\\'| '$') {buf.append((char)$c);}
-		|	'\\$' {buf.append("$");}
+		|	'\\$' {buf.append('$');}
 		|	'\\' c=~('$') {buf.append('\\').append((char)$c);}
+		|	{!isIDStartChar(input.LA(2))}? => '$' {buf.append('$');}
 		)+
 	;
 

tool/test/org/antlr/v4/test/TestActionTranslation.java

@@ -73,6 +73,20 @@ public class TestActionTranslation extends BaseTest {
 		testActions(attributeTemplate, "inline2", action, expected);
     }
 
+	/**
+	 * Regression test for "in antlr v4 lexer, $ translation issue in action".
+	 * https://github.com/antlr/antlr4/issues/176
+	 */
+	@Test public void testUnescaped$InAction() throws Exception {
+		String action = "\\$string$";
+		String expected = "$string$";
+		testActions(attributeTemplate, "members", action, expected);
+		testActions(attributeTemplate, "init", action, expected);
+		testActions(attributeTemplate, "inline", action, expected);
+		testActions(attributeTemplate, "finally", action, expected);
+		testActions(attributeTemplate, "inline2", action, expected);
+	}
+
 	@Test public void testEscapedSlash() throws Exception {
 		String action   = "x = '\\n';";  // x = '\n'; -> x = '\n';
 		String expected = "x = '\\n';";