java: dedicated switch expressions test

make tests on preview features disconnected from language level to make them evolve easily

GitOrigin-RevId: f87bbf684355bce7ae97711a0fc9b5861d58f775

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/switchExpressions/SwitchExpressions.java

@@ -0,0 +1,68 @@
+import java.util.Random;
+
+class SwitchExpressions {
+  enum E { E1, E2 }
+
+  void m() {
+    System.out.println(switch (new Random().nextInt()) {
+      default -> "whatever";
+    });
+
+    System.out.println(switch (<error descr="'switch' expression does not have any case clauses">new Random().nextInt()</error>) { });
+
+    System.out.println(switch (new Random().nextInt()) {
+      case 0 -> throw new IllegalStateException("no args");
+      <error descr="Different case kinds used in the switch">case 1:</error> break "lone";
+    });
+
+    System.out.println(
+      switch (<error descr="Incompatible types. Found: 'java.lang.Object', required: 'char, byte, short, int, Character, Byte, Short, Integer, String, or an enum'">new Object()</error>) {
+        default -> "whatever";
+      }
+    );
+
+    System.out.println(switch (E.valueOf("E1")) {
+      case <error descr="Constant expression required">null</error> -> 0;
+      case <error descr="An enum switch case label must be the unqualified name of an enumeration constant">E.E1</error> -> 1;
+      case E2 -> 2;
+      case <error descr="Incompatible types. Found: 'int', required: 'SwitchExpressions.E'">1</error> -> 1;
+    });
+
+    System.out.println(switch (new Random().nextInt()) {
+      <error descr="Duplicate default label">default</error> -> -1;
+      case 1 -> 1;
+      <error descr="Duplicate default label">default</error> -> 0;
+    });
+
+    System.out.println(switch (<error descr="'switch' expression does not cover all possible input values">new Random().nextInt()</error>) {
+      case 1 -> 1;
+    });
+    System.out.println(switch (<error descr="'switch' expression does not cover all possible input values">E.valueOf("E1")</error>) {
+      case E1 -> 1;
+    });
+    System.out.println(switch (E.valueOf("E1")) {
+      case E1 -> 1;
+      case E2 -> 2;
+    });
+
+    lab: while (true) {
+      switch (new Random().nextInt()) {
+        case -1: return;
+        case -2: continue lab;
+        default: break lab;
+      }
+      System.out.println(switch (new Random().nextInt()) {
+        case -1: <error descr="Return outside of enclosing switch expression">return;</error>
+        case -2: <error descr="Continue outside of enclosing switch expression">continue lab;</error>
+        case -3: <error descr="Continue outside of enclosing switch expression">continue;</error>
+        default: <error descr="Break outside of enclosing switch expression">break lab;</error>
+      });
+    }
+  }
+  
+  enum Empty {}
+  
+  boolean testEmpty(Empty e) {
+    return switch (<error descr="'switch' expression does not have any case clauses">e</error>) {};
+  }
+}