[WASM] Make sure that EmbeddedStatements that return a value never …

…exit without going through an explicit `YieldStatement`.

PiperOrigin-RevId: 724486775

transpiler/java/com/google/j2cl/transpiler/backend/wasm/ExpressionTranspiler.java

@@ -345,6 +345,14 @@ public boolean enterEmbeddedStatement(EmbeddedStatement embeddedStatement) {
             " (result " + environment.getWasmType(embeddedStatement.getTypeDescriptor()) + ")");
 
         StatementTranspiler.render(statement, sourceBuilder, environment);
+        if (!TypeDescriptors.isPrimitiveVoid(embeddedStatement.getTypeDescriptor())) {
+          // If the embedded statement returns a value, it should have an explicit yield and never
+          // reach the end; we add an unreachable instruction at the end to make the code
+          // verifiable. This prevents wasm from rejecting exhaustive switch expressions that will
+          // never reach this point but wouldn't be verifiable in the resulting wasm.
+          sourceBuilder.newLine();
+          sourceBuilder.append("(unreachable)");
+        }
         sourceBuilder.closeParens();
         return false;
       }

transpiler/javatests/com/google/j2cl/readable/java/jsenum/Main.java

@@ -19,7 +19,6 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.Optional;
-import javaemul.internal.annotations.Wasm;
 import jsinterop.annotations.JsEnum;
 import jsinterop.annotations.JsFunction;
 import jsinterop.annotations.JsMethod;
@@ -146,8 +145,6 @@ public static void testJsEnumSwitch() {
     acceptsSupplierOfSupplier(() -> (() -> ComparableJsEnum.ONE));
   }
 
-  // TODO(b/395108282): Remove nop once the bug is fixed.
-  @Wasm("nop")
   private static void testExhaustiveJsEnumSwitchExpression() {
     ComparableJsEnum comparableJsEnum =
         ComparableJsEnum.ONE.getValue() == 1 ? ComparableJsEnum.TWO : null;