size!=cardinality with BitSet.

runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java

@@ -255,7 +255,7 @@ import java.util.Set;
 
 */
 public class ParserATNSimulator extends ATNSimulator {
-	public static boolean debug = false;
+	public static boolean debug = true;
 	public static boolean debug_list_atn_decisions = false;
 	public static boolean dfa_debug = false;
 	public static boolean retry_debug = false;
@@ -672,6 +672,7 @@ public class ParserATNSimulator extends ATNSimulator {
 
 			if ( debug ) {
 				System.out.println("SLL altSubSets="+altSubSets+
+								   ", configs="+reach+
 								   ", predict="+predictedAlt+", allSubsetsConflict="+
 								   allSubsetsConflict(altSubSets)+", conflictingAlts="+
 								   getConflictingAlts(reach));
@@ -753,7 +754,7 @@ public class ParserATNSimulator extends ATNSimulator {
 					BitSet alts = evalSemanticContext(D.predicates, outerContext, true);
 					D.prediction = ATN.INVALID_ALT_NUMBER; // indicate we have preds
 					addDFAEdge(dfa, previousD, t, D);
-					switch (alts.size()) {
+					switch (alts.cardinality()) {
 					case 0:
 						throw noViableAlt(input, outerContext, D.configs, startIndex);
 
@@ -828,15 +829,12 @@ public class ParserATNSimulator extends ATNSimulator {
 				System.out.println("LL altSubSets="+altSubSets+
 								   ", predict="+getUniqueAlt(altSubSets)+
 								   ", resolvesToJustOneViableAlt="+
-								   resolvesToJustOneViableAlt(altSubSets)+
+								   resolvesToJustOneViableAlt(altSubSets));
-								   ", conflictingAlts="+
-								   getConflictingAlts(reach));
 			}
 
 //			System.out.println("altSubSets: "+altSubSets);
 			reach.uniqueAlt = getUniqueAlt(altSubSets);
 			if ( reach.uniqueAlt!=ATN.INVALID_ALT_NUMBER ) break;
-			reach.conflictingAlts = getConflictingAlts(reach);
 			if ( resolvesToJustOneViableAlt(altSubSets) ) break;
 			previous = reach;
 			input.consume();
@@ -878,7 +876,7 @@ public class ParserATNSimulator extends ATNSimulator {
 			reportAmbiguity(dfa, D, startIndex, input.index(), reach.conflictingAlts, reach);
 		}
 
-		return reach.conflictingAlts.nextSetBit(0);
+		return getConflictingAlts(reach).nextSetBit(0);
 	}
 
 	protected ATNConfigSet computeReachSet(ATNConfigSet closure, int t,

tool/playground/T.g

@@ -1,10 +1,12 @@
 grammar T;
-s   : expr expr 
+s   :   expr[0] ;
-    | expr
+
+expr[int _p]
+    :   ID
+        ( {5 >= $_p}? '*' expr[6]
+        | {4 >= $_p}? '+' expr[5]
+        )*
     ;
-expr: '@'
+
-    | ID '@'
+ID  :   [a-zA-Z]+ ;      // match identifiers
-    | ID
+WS  :   [ \t\r\n]+ -> skip ; // toss out whitespace
-    ;
-ID  : [a-z]+ ;
-WS  : [ \r\n\t]+ -> skip ;

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

@@ -247,8 +247,33 @@ public class TestFullContextParsing extends BaseTest {
 		assertEquals("pass: a(i)<-x\n", found);
 
 		String expecting =
-			"line 1:3 reportAttemptingFullContext d=3, input='a(i)'\n" +
+			"line 1:7 reportAttemptingFullContext d=3, input='a(i)<-x'\n" +
-			"line 1:7 reportAmbiguity d=3: ambigAlts={2..3}, input='a(i)<-x'\n";
+			"line 1:7 reportAmbiguity d=3: ambigAlts={2, 3}, input='a(i)<-x'\n";
+		assertEquals(expecting, this.stderrDuringParse);
+	}
+
+	@Test
+	public void testTrueAmbiguityNoLoop() throws Exception {
+		// simpler version of testLoopsSimulateTailRecursion, no loops
+		String grammar =
+			"grammar T;\n" +
+			"prog: expr expr {System.out.println(\"alt 1\");}\n" +
+			"    | expr\n" +
+			"    ;\n" +
+			"expr: '@'\n" +
+			"    | ID '@'\n" +
+			"    | ID\n" +
+			"    ;\n" +
+			"ID  : [a-z]+ ;\n" +
+			"WS  : [ \r\n\t]+ -> skip ;\n";
+
+		String found = execParser("T.g4", grammar, "TParser", "TLexer", "prog", "a@", true);
+		assertEquals("alt 1\n", found);
+
+		String expecting =
+			"line 1:2 reportAmbiguity d=0: ambigAlts={1, 2}, input='a@'\n" +
+			"line 1:2 reportAttemptingFullContext d=1, input='a@'\n" +
+			"line 1:2 reportContextSensitivity d=1, input='a@'\n";
 		assertEquals(expecting, this.stderrDuringParse);
 	}
 

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

@@ -331,7 +331,7 @@ public class TestLeftRecursion extends BaseTest {
 		assertEquals("line 1:1 reportAttemptingFullContext d=3, input='+'\n" +
 					 "line 1:1 reportContextSensitivity d=3, input='+'\n" +
 					 "line 1:3 reportAttemptingFullContext d=3, input='*'\n" +
-					 "line 1:3 reportAmbiguity d=3: ambigAlts={1..2}, input='*'\n",
+					 "line 1:3 reportAmbiguity d=3: ambigAlts={1, 2}, input='*'\n",
 					 stderrDuringParse);
 
 		result = execParser("Expr.g4", grammar, "ExprParser", "ExprLexer", "prog", "(1+2)*3\n", true);

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

@@ -35,6 +35,24 @@ public class TestSemPredEvalParser extends BaseTest {
 	// TEST VALIDATING PREDS
 
 	@Test public void testSimpleValidate() throws Exception {
+		String grammar =
+			"grammar T;\n" +
+				"s : a ;\n" +
+				"a : {false}? ID  {System.out.println(\"alt 1\");}\n" +
+				"  | {true}?  INT {System.out.println(\"alt 2\");}\n" +
+				"  ;\n" +
+				"ID : 'a'..'z'+ ;\n" +
+				"INT : '0'..'9'+;\n" +
+				"WS : (' '|'\\n') {skip();} ;\n";
+
+		String found = execParser("T.g4", grammar, "TParser", "TLexer", "s",
+								  "x", false);
+
+		String expecting = "line 1:0 no viable alternative at input 'x'\n";
+		assertEquals(expecting, stderrDuringParse);
+	}
+
+	@Test public void testSimpleValidate2() throws Exception {
 		String grammar =
 			"grammar T;\n" +
 				"s : a a a;\n" +
@@ -154,9 +172,9 @@ public class TestSemPredEvalParser extends BaseTest {
 			"alt 1\n";
 		assertEquals(expecting, found);
 		assertEquals("line 1:0 reportAttemptingFullContext d=0, input='x'\n" +
-					 "line 1:0 reportAmbiguity d=0: ambigAlts={1..2}, input='x'\n" +
+					 "line 1:0 reportAmbiguity d=0: ambigAlts={1, 2}, input='x'\n" +
 					 "line 1:3 reportAttemptingFullContext d=0, input='y'\n" +
-					 "line 1:3 reportAmbiguity d=0: ambigAlts={1..2}, input='y'\n",
+					 "line 1:3 reportAmbiguity d=0: ambigAlts={1, 2}, input='y'\n",
                      this.stderrDuringParse);
 	}
 
@@ -188,9 +206,9 @@ public class TestSemPredEvalParser extends BaseTest {
 			"alt 2\n";
 		assertEquals(expecting, found);
 		assertEquals("line 1:4 reportAttemptingFullContext d=0, input='x'\n" +
-					 "line 1:4 reportAmbiguity d=0: ambigAlts={2..3}, input='x'\n" +
+					 "line 1:4 reportAmbiguity d=0: ambigAlts={2, 3}, input='x'\n" +
 					 "line 1:7 reportAttemptingFullContext d=0, input='y'\n" +
-					 "line 1:7 reportAmbiguity d=0: ambigAlts={2..3}, input='y'\n",
+					 "line 1:7 reportAmbiguity d=0: ambigAlts={2, 3}, input='y'\n",
 					 this.stderrDuringParse);
 	}