[cfe] Add test for issue 42540

Closes #42540

Change-Id: I8ea8f03a2682a5b52867787144a2d81c7527ca11
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153340
Reviewed-by: Dmitry Stefantsov <dmitryas@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>

pkg/front_end/testcases/nnbd/issue42540.dart

@@ -0,0 +1,12 @@
+// Copyright (c) 2020, 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.
+
+dynamic getNull() => null;
+
+Future<Object> fn() async {
+  Object o = await getNull();
+  return await getNull();
+}
+
+main() {}

pkg/front_end/testcases/nnbd/issue42540.dart.outline.expect

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+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:async" as asy;
+import "dart:core" as core;
+
+static method getNull() → dynamic
+  ;
+static method fn() → asy::Future<core::Object>
+  ;
+static method main() → dynamic
+  ;

pkg/front_end/testcases/nnbd/issue42540.dart.strong.expect

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+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:async" as asy;
+import "dart:core" as core;
+
+static method getNull() → dynamic
+  return null;
+static method fn() → asy::Future<core::Object> async {
+  core::Object o = await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} core::Object;
+  return await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::Object>;
+}
+static method main() → dynamic {}

pkg/front_end/testcases/nnbd/issue42540.dart.strong.transformed.expect

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+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:async" as asy;
+import "dart:core" as core;
+
+static method getNull() → dynamic
+  return null;
+static method fn() → asy::Future<core::Object> /* originally async */ {
+  final asy::_AsyncAwaitCompleter<core::Object> :async_completer = new asy::_AsyncAwaitCompleter::•<core::Object>();
+  FutureOr<core::Object>? :return_value;
+  dynamic :async_stack_trace;
+  (dynamic) → dynamic :async_op_then;
+  (core::Object, core::StackTrace) → dynamic :async_op_error;
+  core::int :await_jump_var = 0;
+  dynamic :await_ctx_var;
+  dynamic :saved_try_context_var0;
+  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
+    try {
+      #L1:
+      {
+        [yield] let dynamic #t1 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
+        core::Object o = let dynamic #t2 = :result in #t2.==(null) ?{core::Object} #t2 as{TypeError,ForDynamic,ForNonNullableByDefault} core::Object : #t2{core::Object};
+        [yield] let dynamic #t3 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
+        :return_value = let dynamic #t4 = :result in #t4.==(null) ?{FutureOr<core::Object>} #t4 as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::Object> : #t4{FutureOr<core::Object>};
+        break #L1;
+      }
+      asy::_completeOnAsyncReturn(:async_completer, :return_value);
+      return;
+    }
+    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
+      :async_completer.{asy::Completer::completeError}(exception, stack_trace);
+    }
+  :async_stack_trace = asy::_asyncStackTraceHelper(:async_op);
+  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
+  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
+  :async_completer.{asy::_AsyncAwaitCompleter::start}(:async_op);
+  return :async_completer.{asy::Completer::future};
+}
+static method main() → dynamic {}

pkg/front_end/testcases/nnbd/issue42540.dart.textual_outline.expect

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+dynamic getNull() => null;
+Future<Object> fn() async {}
+main() {}

pkg/front_end/testcases/nnbd/issue42540.dart.textual_outline_modelled.expect

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+Future<Object> fn() async {}
+dynamic getNull() => null;
+main() {}

pkg/front_end/testcases/nnbd/issue42540.dart.weak.expect

@@ -0,0 +1,12 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:async" as asy;
+import "dart:core" as core;
+
+static method getNull() → dynamic
+  return null;
+static method fn() → asy::Future<core::Object> async {
+  core::Object o = await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} core::Object;
+  return await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::Object>;
+}
+static method main() → dynamic {}

pkg/front_end/testcases/nnbd/issue42540.dart.weak.transformed.expect

@@ -0,0 +1,39 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:async" as asy;
+import "dart:core" as core;
+
+static method getNull() → dynamic
+  return null;
+static method fn() → asy::Future<core::Object> /* originally async */ {
+  final asy::_AsyncAwaitCompleter<core::Object> :async_completer = new asy::_AsyncAwaitCompleter::•<core::Object>();
+  FutureOr<core::Object>? :return_value;
+  dynamic :async_stack_trace;
+  (dynamic) → dynamic :async_op_then;
+  (core::Object, core::StackTrace) → dynamic :async_op_error;
+  core::int :await_jump_var = 0;
+  dynamic :await_ctx_var;
+  dynamic :saved_try_context_var0;
+  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
+    try {
+      #L1:
+      {
+        [yield] let dynamic #t1 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
+        core::Object o = :result;
+        [yield] let dynamic #t2 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
+        :return_value = :result;
+        break #L1;
+      }
+      asy::_completeOnAsyncReturn(:async_completer, :return_value);
+      return;
+    }
+    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
+      :async_completer.{asy::Completer::completeError}(exception, stack_trace);
+    }
+  :async_stack_trace = asy::_asyncStackTraceHelper(:async_op);
+  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
+  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
+  :async_completer.{asy::_AsyncAwaitCompleter::start}(:async_op);
+  return :async_completer.{asy::Completer::future};
+}
+static method main() → dynamic {}