[dart2js] Fix #47566 by disabling optimization

The JavaScript-to-JavaScript async transform had an inconsisent
handling of switch statements that contained an await, but only in the
expression.

For now the special handling of the expression-only case is disabled.

Change-Id: Ia79ff3951d681ba933df638da7e0e518d401ed9a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/219746
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Commit-Queue: Stephen Adams <sra@google.com>

pkg/compiler/lib/src/js/rewrite_async.dart

@@ -1397,8 +1397,8 @@ abstract class AsyncRewriterBase extends js.NodeVisitor {
 
   @override
   void visitSwitch(js.Switch node) {
-    if (!node.cases.any(shouldTransform)) {
-      // If only the key has an await, translation can be simplified.
+    if (!shouldTransform(node)) {
+      // TODO(sra): If only the key has an await, translation can be simplified.
       bool oldInsideUntranslated = insideUntranslatedBreakable;
       insideUntranslatedBreakable = true;
       withExpression(node.key, (js.Expression key) {
@@ -2824,10 +2824,9 @@ class PreTranslationAnalysis extends js.BaseVisitor<bool> {
   @override
   bool visitSwitch(js.Switch node) {
     loopsAndSwitches.add(node);
-    // If the key has an `await` expression, do not transform the
-    // body of the switch.
-    visit(node.key);
-    bool result = false;
+    // TODO(sra): If just the key has an `await` expression, do not transform
+    // the body of the switch.
+    bool result = visit(node.key);
     for (js.SwitchClause clause in node.cases) {
       if (visit(clause)) result = true;
     }

pkg/compiler/test/async_await/async_await_js_transform_test.dart

@@ -1085,20 +1085,116 @@ function(l) {
       switch (__goto) {
         case 0:
           // Function start
-          __goto = 2;
-          return awaitHelper(l, body);
         case 2:
+          // switch
+          __goto = 7;
+          return awaitHelper(l, body);
+        case 7:
           // returning from await.
           switch (__result) {
             case 1:
-              print(1);
+              // goto case
+              __goto = 4;
               break;
             case 2:
-              print(1);
+              // goto case
+              __goto = 5;
+              break;
             default:
-              print(2);
+              // goto default
+              __goto = 6;
               break;
           }
+          break;
+        case 4:
+          // case
+          print(1);
+          // goto after switch
+          __goto = 3;
+          break;
+        case 5:
+          // case
+          print(1);
+        case 6:
+          // default
+          print(2);
+          // goto after switch
+          __goto = 3;
+          break;
+        case 3:
+          // after switch
+          // implicit return
+          return returnHelper(null, __completer);
+      }
+  });
+  return startHelper(body, __completer);
+}""");
+
+  testAsyncTransform("""
+  // This example is like #47566
+  function(b, l) async {
+    print("start");
+    if (b) {
+      switch(await l) {
+        case 1:
+          print(1);
+          break;
+        default:
+          print(2);
+          break;
+      }
+    }
+    print("end");
+  }""", """
+function(b, l) {
+  var __goto = 0,
+    __completer = NewCompleter(CompleterType);
+  var body = _wrapJsFunctionForAsync(function(__errorCode, __result) {
+    if (__errorCode === 1)
+      return rethrowHelper(__result, __completer);
+    while (true)
+      switch (__goto) {
+        case 0:
+          // Function start
+          print("start");
+          __goto = b ? 2 : 3;
+          break;
+        case 2:
+          // then
+        case 4:
+          // switch
+          __goto = 8;
+          return awaitHelper(l, body);
+        case 8:
+          // returning from await.
+          switch (__result) {
+            case 1:
+              // goto case
+              __goto = 6;
+              break;
+            default:
+              // goto default
+              __goto = 7;
+              break;
+          }
+          break;
+        case 6:
+          // case
+          print(1);
+          // goto after switch
+          __goto = 5;
+          break;
+        case 7:
+          // default
+          print(2);
+          // goto after switch
+          __goto = 5;
+          break;
+        case 5:
+          // after switch
+        case 3:
+          // join
+          print("end");
           // implicit return
           return returnHelper(null, __completer);
       }

tests/language/regress/regress47566_test.dart

@@ -0,0 +1,42 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Regression test for https://github.com/dart-lang/sdk/issues/47566
+
+import 'package:expect/expect.dart';
+
+final List trace = [];
+void log(String s) {
+  trace.add(s);
+}
+
+Future<void> test(bool value) async {
+  log('f1');
+
+  if (value) {
+    final result = await bar();
+    switch (result) {
+      case 1:
+        log('sb');
+        break;
+      case 0:
+        return;
+    }
+    log('sc');
+  }
+
+  log('f2');
+}
+
+Future<int> bar() async => 1;
+
+Future<void> main() async {
+  trace.clear();
+  await test(true);
+  Expect.equals('f1,sb,sc,f2', trace.join(','));
+
+  trace.clear();
+  await test(false);
+  Expect.equals('f1,f2', trace.join(','));
+}