8335766: Switch case with pattern matching and guard clause compiles inconsistently

Reviewed-by: abimpoudis

Author: lahodaj

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

@@ -3436,7 +3436,15 @@ PatternResult analyzePattern(int lookahead) {
                                 : PatternResult.PATTERN;
                     }
                     parenDepth++; break;
-                case RPAREN: parenDepth--; break;
+                case RPAREN:
+                    parenDepth--;
+                    if (parenDepth == 0 &&
+                        typeDepth == 0 &&
+                        peekToken(lookahead, TokenKind.IDENTIFIER) &&
+                        S.token(lookahead + 1).name() == names.when) {
+                        return PatternResult.PATTERN;
+                    }
+                    break;
                 case ARROW: return parenDepth > 0 ? PatternResult.EXPRESSION
                                                    : pendingResult;
                 case FINAL:

test/langtools/tools/javac/patterns/DisambiguatePatterns.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -109,6 +109,10 @@ public static void main(String... args) throws Throwable {
                                  ExpressionType.EXPRESSION);
         test.disambiguationTest("a & b",
                                  ExpressionType.EXPRESSION);
+        test.disambiguationTest("R r when (x > 0)",
+                                 ExpressionType.PATTERN);
+        test.disambiguationTest("R(int x) when (x > 0)",
+                                 ExpressionType.PATTERN);
     }
 
     private final ParserFactory factory;