8314578: Non-verifiable code is emitted when two guards declare pattern variables in colon-switch

Reviewed-by: vromero

Author: biboudis

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

@@ -4650,11 +4650,11 @@ void checkSwitchCaseStructure(List<JCCase> cases) {
                 if (previousCompletessNormally &&
                     c.stats.nonEmpty() &&
                     c.labels.head instanceof JCPatternCaseLabel patternLabel &&
-                    hasBindings(patternLabel.pat)) {
+                    (hasBindings(patternLabel.pat) || hasBindings(c.guard))) {
                     log.error(c.labels.head.pos(), Errors.FlowsThroughToPattern);
                 } else if (c.stats.isEmpty() &&
                            c.labels.head instanceof JCPatternCaseLabel patternLabel &&
-                           hasBindings(patternLabel.pat) &&
+                           (hasBindings(patternLabel.pat) || hasBindings(c.guard)) &&
                            hasStatements(l.tail)) {
                     log.error(c.labels.head.pos(), Errors.FlowsThroughFromPattern);
                 }
@@ -4663,7 +4663,7 @@ void checkSwitchCaseStructure(List<JCCase> cases) {
         }
     }
 
-    boolean hasBindings(JCPattern p) {
+    boolean hasBindings(JCTree p) {
         boolean[] bindings = new boolean[1];
 
         new TreeScanner() {

test/langtools/tools/javac/patterns/T8314578.java

@@ -0,0 +1,43 @@
+/**
+ * @test /nodynamiccopyright/
+ * @bug 8314578
+ * @enablePreview
+ * @summary Parsing of erroneous patterns succeeds
+ * @compile/fail/ref=T8314578.out -XDrawDiagnostics T8314578.java
+ */
+public class T8314578 {
+    record R1() {}
+    record R2() {}
+
+    static void test(Object o) {
+        switch (o) {
+            case R1() when o instanceof String s:
+            case R2() when o instanceof Integer i:
+                System.out.println("hello: " + i);
+                break;
+            default:
+                break;
+        }
+    }
+
+    static void test2(Object o) {
+        switch (o) {
+            case R1() when o instanceof String s:
+                System.out.println("hello: " + s);
+            case R2() when o instanceof Integer i:
+                System.out.println("hello: " + i);
+                break;
+            default:
+                break;
+        }
+    }
+
+    static int unnamedInGuardsOK(String s) {
+        return switch (s) {
+            case String _ when s instanceof String _ ->  // should be OK
+                    1;
+            default ->
+                    -1;
+        };
+    }
+}

test/langtools/tools/javac/patterns/T8314578.out

@@ -0,0 +1,6 @@
+T8314578.java:14:18: compiler.err.flows.through.from.pattern
+T8314578.java:15:18: compiler.err.flows.through.to.pattern
+T8314578.java:27:18: compiler.err.flows.through.to.pattern
+- compiler.note.preview.filename: T8314578.java, DEFAULT
+- compiler.note.preview.recompile
+3 errors