Add compiler warning 157: UNRECOGNIZED_ASSOC_OPTION (fixes #489)

tool/src/org/antlr/v4/analysis/LeftRecursiveRuleTransformer.java

@@ -152,6 +152,9 @@ public class LeftRecursiveRuleTransformer {
 		RuleCollector ruleCollector = new RuleCollector(g);
 		ruleCollector.visit(t, "rule");
 		BasicSemanticChecks basics = new BasicSemanticChecks(g, ruleCollector);
+		// disable the assoc element option checks because they are already
+		// handled for the pre-transformed rule.
+		basics.checkAssocElementOption = false;
 		basics.visit(t, "rule");
 
 		// track recursive alt info for codegen

tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java

@@ -101,6 +101,15 @@ public class BasicSemanticChecks extends GrammarTreeVisitor {
 	public RuleCollector ruleCollector;
 	public ErrorManager errMgr;
 
+	/**
+	 * When this is {@code true}, the semantic checks will report
+	 * {@link ErrorType#UNRECOGNIZED_ASSOC_OPTION} where appropriate. This may
+	 * be set to {@code false} to disable this specific check.
+	 *
+	 * <p>The default value is {@code true}.</p>
+	 */
+	public boolean checkAssocElementOption = true;
+
 	/**
 	 * This field is used for reporting the {@link ErrorType#MODE_WITHOUT_RULES}
 	 * error when necessary.
@@ -477,6 +486,17 @@ public class BasicSemanticChecks extends GrammarTreeVisitor {
 								GrammarAST ID,
 								GrammarAST valueAST)
 	{
+		if (checkAssocElementOption && ID != null && "assoc".equals(ID.getText())) {
+			if (elem.getType() != ANTLRParser.ALT) {
+				Token optionID = ID.token;
+				String fileName = optionID.getInputStream().getSourceName();
+				g.tool.errMgr.grammarError(ErrorType.UNRECOGNIZED_ASSOC_OPTION,
+										   fileName,
+										   optionID,
+										   currentRuleName);
+			}
+		}
+
 		if ( elem instanceof TerminalAST ) {
 			return checkTokenOptions((TerminalAST)elem, ID, valueAST);
 		}

tool/src/org/antlr/v4/tool/ErrorType.java

@@ -826,6 +826,32 @@ public enum ErrorType {
 	 * @since 4.2.1
 	 */
 	INVALID_ESCAPE_SEQUENCE(156, "invalid escape sequence", ErrorSeverity.ERROR),
+	/**
+	 * Compiler Warning 157.
+	 *
+	 * <p>rule '<em>rule</em>' contains an 'assoc' element option in an
+	 * unrecognized location</p>
+	 *
+	 * <p>
+	 * In ANTLR 4.2, the position of the {@code assoc} element option was moved
+	 * from the operator terminal(s) to the alternative itself. This warning is
+	 * reported when an {@code assoc} element option is specified on a grammar
+	 * element that is not recognized by the current version of ANTLR, and as a
+	 * result will simply be ignored.
+	 * </p>
+	 *
+	 * <p>The following rule produces this warning.</p>
+	 *
+	 * <pre>
+	 * x : 'x'
+	 *   | x '+'&lt;assoc=right&gt; x   // warning 157
+	 *   |&lt;assoc=right&gt; x '*' x   // ok
+	 *   ;
+	 * </pre>
+	 *
+	 * @since 4.2.1
+	 */
+	UNRECOGNIZED_ASSOC_OPTION(157, "rule '<arg>' contains an 'assoc' terminal option in an unrecognized location", ErrorSeverity.WARNING),
 
 	/*
 	 * Backward incompatibility errors

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

@@ -451,4 +451,26 @@ public class TestToolSyntaxErrors extends BaseTest {
 
 		super.testErrors(pair, true);
 	}
+
+	/**
+	 * This test ensures the {@link ErrorType#UNRECOGNIZED_ASSOC_OPTION} warning
+	 * is produced as described in the documentation.
+	 */
+	@Test public void testUnrecognizedAssocOption() {
+		String grammar =
+			"grammar A;\n" +
+			"x : 'x'\n" +
+			"  | x '+'<assoc=right> x   // warning 157\n" +
+			"  |<assoc=right> x '*' x   // ok\n" +
+			"  ;\n";
+		String expected =
+			"warning(" + ErrorType.UNRECOGNIZED_ASSOC_OPTION.code + "): A.g4:3:10: rule 'x' contains an 'assoc' terminal option in an unrecognized location\n";
+
+		String[] pair = new String[] {
+			grammar,
+			expected
+		};
+
+		super.testErrors(pair, true);
+	}
 }