[cfe] Handle typed variable declarations during top-level inference

Fixes flutter/flutter#50908

Change-Id: Ia7a04351eb9f2a557bb70c96c7938a28c8cbc835
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/136127
Reviewed-by: Dmitry Stefantsov <[email protected]>
Commit-Queue: Johnni Winther <[email protected]>

Author: johnniwinther

pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart

@@ -1874,6 +1874,10 @@ class TypeInferrerImpl implements TypeInferrer {
   /// Modifies a type as appropriate when inferring a declared variable's type.
   DartType inferDeclarationType(DartType initializerType,
       {bool forSyntheticVariable: false}) {
+    if (initializerType == null) {
+      assert(isTopLevel, "No initializer type provided.");
+      return null;
+    }
     if (initializerType is BottomType ||
         (initializerType is InterfaceType &&
             initializerType.classNode == coreTypes.nullClass)) {

pkg/front_end/testcases/general/infer_map_literal_with_closure.dart

@@ -0,0 +1,13 @@
+// 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.
+
+class Class {
+  var map = {
+    'foo': (String a) {
+      int c = a.length;
+    }
+  };
+}
+
+main() {}

pkg/front_end/testcases/general/infer_map_literal_with_closure.dart.outline.expect

@@ -0,0 +1,11 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class Class extends core::Object {
+  field core::Map<core::String*, (core::String*) →* core::Null?>* map;
+  synthetic constructor •() → self::Class*
+    ;
+}
+static method main() → dynamic
+  ;

pkg/front_end/testcases/general/infer_map_literal_with_closure.dart.strong.expect

@@ -0,0 +1,13 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class Class extends core::Object {
+  field core::Map<core::String*, (core::String*) →* core::Null?>* map = <core::String*, (core::String*) →* core::Null?>{"foo": (core::String* a) → core::Null? {
+    core::int* c = a.{core::String::length};
+  }};
+  synthetic constructor •() → self::Class*
+    : super core::Object::•()
+    ;
+}
+static method main() → dynamic {}

pkg/front_end/testcases/general/infer_map_literal_with_closure.dart.strong.transformed.expect

@@ -0,0 +1,13 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class Class extends core::Object {
+  field core::Map<core::String*, (core::String*) →* core::Null?>* map = <core::String*, (core::String*) →* core::Null?>{"foo": (core::String* a) → core::Null? {
+    core::int* c = a.{core::String::length};
+  }};
+  synthetic constructor •() → self::Class*
+    : super core::Object::•()
+    ;
+}
+static method main() → dynamic {}

pkg/front_end/testcases/text_serialization.status

@@ -206,6 +206,7 @@ general/import_conflicting_type_member: TextSerializationFailure
 general/import_conflicting_types: TextSerializationFailure
 general/incomplete_field_formal_parameter: TextSerializationFailure # Was: RuntimeError
 general/infer_field_from_multiple: TypeCheckError
+general/infer_map_literal_with_closure: TextSerializationFailure
 general/interface_contravariant_from_class: TextSerializationFailure
 general/interface_covariantImpl_from_class: TextSerializationFailure
 general/interface_covariantInterface_from_class: TextSerializationFailure