[cfe/ffi] Fix Struct invalid field crashes

Closes: https://github.com/dart-lang/sdk/issues/44985
Closes: https://github.com/dart-lang/sdk/issues/44986

TEST=tests/ffi(_2)/regress_4498[56]_test.dart

Change-Id: Ia21e6e41de14ef61843ce9bff0608a9235f08936
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/185860
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>

pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart

@@ -3855,6 +3855,30 @@ Message _withArgumentsFfiFieldNoAnnotation(String name) {
       arguments: {'name': name});
 }
 
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Template<
+    Message Function(String name)> templateFfiFieldNull = const Template<
+        Message Function(String name)>(
+    messageTemplate:
+        r"""Field '#name' cannot have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct`.""",
+    withArguments: _withArgumentsFfiFieldNull);
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Message Function(String name)> codeFfiFieldNull =
+    const Code<Message Function(String name)>(
+  "FfiFieldNull",
+);
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+Message _withArgumentsFfiFieldNull(String name) {
+  if (name.isEmpty) throw 'No name provided';
+  name = demangleMixinApplicationName(name);
+  return new Message(codeFfiFieldNull,
+      message:
+          """Field '${name}' cannot have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct`.""",
+      arguments: {'name': name});
+}
+
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Template<
     Message Function(String name)> templateFfiNotStatic = const Template<

pkg/front_end/lib/src/api_unstable/vm.dart

@@ -62,6 +62,7 @@ export '../fasta/fasta_codes.dart'
         templateFfiFieldCyclic,
         templateFfiFieldInitializer,
         templateFfiFieldNoAnnotation,
+        templateFfiFieldNull,
         templateFfiNotStatic,
         templateFfiStructGeneric,
         templateFfiTypeInvalid,

pkg/front_end/messages.status

@@ -327,6 +327,7 @@ FfiFieldAnnotation/analyzerCode: Fail
 FfiFieldCyclic/analyzerCode: Fail
 FfiFieldInitializer/analyzerCode: Fail
 FfiFieldNoAnnotation/analyzerCode: Fail
+FfiFieldNull/analyzerCode: Fail
 FfiNotStatic/analyzerCode: Fail
 FfiStructAnnotation/analyzerCode: Fail
 FfiStructGeneric/analyzerCode: Fail

pkg/front_end/messages.yaml

@@ -4225,6 +4225,11 @@ FfiTypeInvalid:
   template: "Expected type '#type' to be a valid and instantiated subtype of 'NativeType'."
   external: test/ffi_test.dart
 
+FfiFieldNull:
+  # Used by dart:ffi
+  template: "Field '#name' cannot have type 'Null', it must be `int`, `double`, `Pointer`, or a subtype of `Struct`."
+  external: test/ffi_test.dart
+
 FfiFieldAnnotation:
   # Used by dart:ffi
   template: "Field '#name' requires exactly one annotation to declare its native type, which cannot be Void. dart:ffi Structs cannot have regular Dart fields."

pkg/vm/lib/transformations/ffi_definitions.dart

@@ -10,6 +10,7 @@ import 'package:front_end/src/api_unstable/vm.dart'
     show
         templateFfiEmptyStruct,
         templateFfiFieldAnnotation,
+        templateFfiFieldNull,
         templateFfiFieldCyclic,
         templateFfiFieldNoAnnotation,
         templateFfiTypeMismatch,
@@ -227,6 +228,14 @@ class _FfiDefinitionTransformer extends FfiTransformer {
     if (type is InvalidType) {
       return false;
     }
+    if (type is NullType) {
+      return false;
+    }
+    if (type is InterfaceType) {
+      if (type.classNode == structClass) {
+        return false;
+      }
+    }
     return env.isSubtypeOf(type, InterfaceType(structClass, Nullability.legacy),
         SubtypeCheckMode.ignoringNullabilities);
   }
@@ -279,7 +288,15 @@ class _FfiDefinitionTransformer extends FfiTransformer {
       }
       final nativeTypeAnnos = _getNativeTypeAnnotations(f).toList();
       final type = _structFieldMemberType(f);
-      if (_isPointerType(type) || _isStructSubtype(type)) {
+      if (type is NullType) {
+        diagnosticReporter.report(
+            templateFfiFieldNull.withArguments(f.name.text),
+            f.fileOffset,
+            f.name.text.length,
+            f.fileUri);
+        // This class is invalid, but continue reporting other errors on it.
+        success = false;
+      } else if (_isPointerType(type) || _isStructSubtype(type)) {
         if (nativeTypeAnnos.length != 0) {
           diagnosticReporter.report(
               templateFfiFieldNoAnnotation.withArguments(f.name.text),

tests/ffi/regress_44985_test.dart

@@ -0,0 +1,15 @@
+// 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.
+
+import "dart:ffi";
+
+class S2 extends Struct {
+  external Pointer<Int8> notEmpty;
+
+  external Struct? s; //# 01: compile-time error
+}
+
+void main() {
+  S2? s2;
+}

tests/ffi/regress_44986_test.dart

@@ -0,0 +1,15 @@
+// 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.
+
+import "dart:ffi";
+
+class S2 extends Struct {
+  external Pointer<Int8> notEmpty;
+
+  external Null s; //# 01: compile-time error
+}
+
+void main() {
+  S2? s2;
+}

tests/ffi_2/regress_44985_test.dart

@@ -0,0 +1,15 @@
+// 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.
+
+import "dart:ffi";
+
+class S2 extends Struct {
+  Pointer<Int8> notEmpty;
+
+  Struct s; //# 01: compile-time error
+}
+
+void main() {
+  S2 s2;
+}

tests/ffi_2/regress_44986_test.dart

@@ -0,0 +1,15 @@
+// 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.
+
+import "dart:ffi";
+
+class S2 extends Struct {
+  Pointer<Int8> notEmpty;
+
+  Null s; //# 01: compile-time error
+}
+
+void main() {
+  S2 s2;
+}