8312204: unexpected else with statement causes compiler crash

Reviewed-by: vromero

Author: lahodaj

src/jdk.compiler/share/classes/com/sun/tools/javac/parser/VirtualParser.java

@@ -148,12 +148,12 @@ public Token split() {
 
         @Override
         public int errPos() {
-            throw new AssertionError();
+            return S.errPos();
         }
 
         @Override
         public void errPos(int pos) {
-            throw new AssertionError();
+            S.errPos(pos);
         }
 
         @Override

test/langtools/tools/javac/parser/JavacParserTest.java

@@ -23,7 +23,7 @@
 
 /*
  * @test
- * @bug 7073631 7159445 7156633 8028235 8065753 8205418 8205913 8228451 8237041 8253584 8246774 8256411 8256149 8259050 8266436 8267221 8271928 8275097 8293897 8295401 8304671 8310326 8312093
+ * @bug 7073631 7159445 7156633 8028235 8065753 8205418 8205913 8228451 8237041 8253584 8246774 8256411 8256149 8259050 8266436 8267221 8271928 8275097 8293897 8295401 8304671 8310326 8312093 8312204
  * @summary tests error and diagnostics positions
  * @author  Jan Lahoda
  * @modules jdk.compiler/com.sun.tools.javac.api
@@ -2448,6 +2448,44 @@ public Void visitMethod(MethodTree node, Void p) {
         }.scan(cut, null);
     }
 
+    @Test //JDK-8312204
+    void testDanglingElse() throws IOException {
+        String code = """
+                      void main() {
+                          else ;
+                      }
+                      """;
+        DiagnosticCollector<JavaFileObject> coll =
+                new DiagnosticCollector<>();
+        JavacTaskImpl ct = (JavacTaskImpl) tool.getTask(null, fm, coll,
+                List.of("--enable-preview", "--source", SOURCE_VERSION),
+                null, Arrays.asList(new MyFileObject(code)));
+        CompilationUnitTree cut = ct.parse().iterator().next();
+
+        String result = cut.toString().replaceAll("\\R", "\n");
+        System.out.println("RESULT\n" + result);
+        assertEquals("incorrect AST",
+                     result,
+                     """
+                     \n\
+                     /*synthetic*/ final class Test {
+                         \n\
+                         void main() {
+                             (ERROR);
+                         }
+                     }""");
+
+        List<String> codes = new LinkedList<>();
+
+        for (Diagnostic<? extends JavaFileObject> d : coll.getDiagnostics()) {
+            codes.add(d.getLineNumber() + ":" + d.getColumnNumber() + ":" + d.getCode());
+        }
+
+        assertEquals("testDanglingElse: " + codes,
+                     List.of("2:5:compiler.err.else.without.if"),
+                     codes);
+    }
+
     void run(String[] args) throws Exception {
         int passed = 0, failed = 0;
         final Pattern p = (args != null && args.length > 0)