8304694: Runtime exception thrown when break stmt is missing

Reviewed-by: vromero

Author: lahodaj

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/TransPatterns.java

@@ -451,6 +451,7 @@ private void handleSwitch(JCTree tree,
                     return l;
                 });
                 newCases.add(c.head);
+                appendBreakIfNeeded(tree, cases, c.head);
             }
             cases = processCases(tree, newCases.toList());
             ListBuffer<JCStatement> statements = new ListBuffer<>();
@@ -595,7 +596,6 @@ private void handleSwitch(JCTree tree,
                 previousCompletesNormally =
                         c.caseKind == CaseTree.CaseKind.STATEMENT &&
                         c.completesNormally;
-                appendBreakIfNeeded(tree, c);
             }
 
             if (tree.hasTag(Tag.SWITCH)) {
@@ -640,9 +640,11 @@ public void visitCase(JCCase c) {
             }.scan(c.stats);
         }
 
-    private void appendBreakIfNeeded(JCTree switchTree, JCCase c) {
-        if (c.caseKind == CaseTree.CaseKind.RULE) {
-            JCBreak brk = make.at(TreeInfo.endPos(c.stats.last())).Break(null);
+    void appendBreakIfNeeded(JCTree switchTree, List<JCCase> cases, JCCase c) {
+        if (c.caseKind == CaseTree.CaseKind.RULE || (cases.last() == c && c.completesNormally)) {
+            JCTree pos = c.stats.nonEmpty() ? c.stats.last()
+                                            : c;
+            JCBreak brk = make.at(TreeInfo.endPos(pos)).Break(null);
             brk.target = switchTree;
             c.stats = c.stats.append(brk);
         }
@@ -745,7 +747,6 @@ public void resolve(VarSymbol commonBinding,
                         } else {
                             newLabel = List.of(make.PatternCaseLabel(binding, newGuard));
                         }
-                        appendBreakIfNeeded(currentSwitch, accummulated);
                         nestedCases.add(make.Case(CaseKind.STATEMENT, newLabel, accummulated.stats, null));
                         lastGuard = newGuard;
                     }

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

@@ -23,7 +23,7 @@
 
 /**
  * @test
- * @bug 8291769 8301858
+ * @bug 8291769 8301858 8304694
  * @summary Verify more complex switches work properly
  * @compile --enable-preview -source ${jdk.version} DeconstructionDesugaring.java
  * @run main/othervm --enable-preview DeconstructionDesugaring
@@ -45,6 +45,8 @@ private void test() {
         assertEquals(runCheckExpressionWithUnconditional1(new R5(null)), 3);
         assertEquals(runCheckExpressionWithUnconditionalAndParams(new R1(42)), 1);
         assertEquals(runCheckExpressionWithUnconditionalAndParams(new R1(new Object())), 2);
+        assertEquals(runFallThrough(new R6(1, 1)), 0);
+        assertEquals(runFallThrough(new R6(0, 0)), 1);
     }
 
     private void test(ToIntFunction<Object> task) {
@@ -113,6 +115,15 @@ case R1(Object o):
                 return meth_O(o);
         }
     }
+
+    public static int runFallThrough(R6 r) {
+        switch (r) {
+            case R6(var v1, var v2) when v1 != 0: return 0;
+            case R6(var v1, var v2):
+        }
+        return 1;
+    }
+
     public static int meth_I(Integer i) { return 1; }
     public static int meth_O(Object o) { return 2;}
 
@@ -134,4 +145,5 @@ final class Sub3 extends Super {}
 
     record R4(Super o) {}
     record R5(R4 o) {}
+    record R6(int i1, int i2) {}
 }