[vm/ffi] Allow struct nesting with looser packing

C compilers don't enforce nesting rules. `dart:ffi` was enforcing these
rules causing issues for binding to C libraries having looser packing
for nested structs than outer structs.

This CL completely removes the error from the analyzer and CFE.
(As an alternative we could have kept a hint/lint, but this might create
more noise than value.)

TEST=pkg/analyzer/test/src/diagnostics/packed_nesting_non_packed_test.dart

Closes: #46644
Change-Id: Iae2d5c885546f7799bc6dea2f8cd7dd508216a0c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/247382
Commit-Queue: Daco Harkes <[email protected]>
Reviewed-by: Aske Simon Christensen <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: dcharkes

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

@@ -4633,36 +4633,6 @@ const MessageCode messageFfiPackedAnnotationAlignment = const MessageCode(
     problemMessage:
         r"""Only packing to 1, 2, 4, 8, and 16 bytes is supported.""");
 
-// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
-const Template<
-    Message Function(
-        String name,
-        String
-            name2)> templateFfiPackedNestingNonPacked = const Template<
-        Message Function(String name, String name2)>(
-    problemMessageTemplate:
-        r"""Nesting the non-packed or less tightly packed struct '#name' in a packed struct '#name2' is not supported.""",
-    withArguments: _withArgumentsFfiPackedNestingNonPacked);
-
-// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
-const Code<Message Function(String name, String name2)>
-    codeFfiPackedNestingNonPacked =
-    const Code<Message Function(String name, String name2)>(
-  "FfiPackedNestingNonPacked",
-);
-
-// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
-Message _withArgumentsFfiPackedNestingNonPacked(String name, String name2) {
-  if (name.isEmpty) throw 'No name provided';
-  name = demangleMixinApplicationName(name);
-  if (name2.isEmpty) throw 'No name provided';
-  name2 = demangleMixinApplicationName(name2);
-  return new Message(codeFfiPackedNestingNonPacked,
-      problemMessage:
-          """Nesting the non-packed or less tightly packed struct '${name}' in a packed struct '${name2}' is not supported.""",
-      arguments: {'name': name, 'name2': name2});
-}
-
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Template<Message Function(String name)> templateFfiSizeAnnotation =
     const Template<Message Function(String name)>(

pkg/analysis_server/lib/src/services/correction/error_fix_status.yaml

@@ -1193,8 +1193,6 @@ FfiCode.PACKED_ANNOTATION:
   status: needsEvaluation
 FfiCode.PACKED_ANNOTATION_ALIGNMENT:
   status: needsEvaluation
-FfiCode.PACKED_NESTING_NON_PACKED:
-  status: needsEvaluation
 FfiCode.SIZE_ANNOTATION_DIMENSIONS:
   status: needsEvaluation
 FfiCode.SUBTYPE_OF_FFI_CLASS_IN_EXTENDS:

pkg/analyzer/lib/error/error.dart

@@ -539,7 +539,6 @@ const List<ErrorCode> errorCodeValues = [
   FfiCode.NON_SIZED_TYPE_ARGUMENT,
   FfiCode.PACKED_ANNOTATION,
   FfiCode.PACKED_ANNOTATION_ALIGNMENT,
-  FfiCode.PACKED_NESTING_NON_PACKED,
   FfiCode.SIZE_ANNOTATION_DIMENSIONS,
   FfiCode.SUBTYPE_OF_FFI_CLASS_IN_EXTENDS,
   FfiCode.SUBTYPE_OF_FFI_CLASS_IN_IMPLEMENTS,

pkg/analyzer/lib/src/dart/error/ffi_code.g.dart

@@ -369,19 +369,6 @@ class FfiCode extends AnalyzerErrorCode {
     hasPublishedDocs: true,
   );
 
-  ///  Parameters:
-  ///  0: the name of the outer struct
-  ///  1: the name of the struct being nested
-  static const FfiCode PACKED_NESTING_NON_PACKED = FfiCode(
-    'PACKED_NESTING_NON_PACKED',
-    "Nesting the non-packed or less tightly packed struct '{0}' in a packed "
-        "struct '{1}' isn't supported.",
-    correctionMessage:
-        "Try packing the nested struct or packing the nested struct more "
-        "tightly.",
-    hasPublishedDocs: true,
-  );
-
   ///  No parameters.
   static const FfiCode SIZE_ANNOTATION_DIMENSIONS = FfiCode(
     'SIZE_ANNOTATION_DIMENSIONS',

pkg/analyzer/lib/src/generated/ffi_verifier.dart

@@ -943,12 +943,6 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
         }
         final arrayDimensions = declaredType.arrayDimensions;
         _validateSizeOfAnnotation(fieldType, annotations, arrayDimensions);
-        final arrayElement = declaredType.arrayElementType;
-        if (arrayElement.isCompoundSubtype) {
-          final elementClass = (arrayElement as InterfaceType).element;
-          _validatePackingNesting(compound!.declaredElement!, elementClass,
-              errorNode: fieldType);
-        }
       } else if (declaredType.isCompoundSubtype) {
         final clazz = (declaredType as InterfaceType).element;
         if (clazz.isEmptyStruct) {
@@ -957,8 +951,6 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
             clazz.supertype!.getDisplayString(withNullability: false)
           ]);
         }
-        _validatePackingNesting(compound!.declaredElement!, clazz,
-            errorNode: fieldType);
       } else {
         _errorReporter.reportErrorForNode(FfiCode.INVALID_FIELD_TYPE_IN_STRUCT,
             fieldType, [fieldType.toSource()]);
@@ -1124,28 +1116,6 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
     }
   }
 
-  void _validatePackingNesting(ClassElement outer, ClassElement nested,
-      {required TypeAnnotation errorNode}) {
-    final outerPacking = outer.structPacking;
-    if (outerPacking == null) {
-      // No packing for outer class, so we're done.
-      return;
-    }
-    bool error = false;
-    final nestedPacking = nested.structPacking;
-    if (nestedPacking == null) {
-      // The outer struct packs, but the nested struct does not.
-      error = true;
-    } else if (outerPacking < nestedPacking) {
-      // The outer struct packs tighter than the nested struct.
-      error = true;
-    }
-    if (error) {
-      _errorReporter.reportErrorForNode(FfiCode.PACKED_NESTING_NON_PACKED,
-          errorNode, [nested.name, outer.name]);
-    }
-  }
-
   void _validateRefIndexed(IndexExpression node) {
     var targetType = node.realTarget.staticType;
     if (!_isValidFfiNativeType(targetType,
@@ -1484,17 +1454,6 @@ extension on ClassElement {
   bool get isFfiClass {
     return library.name == FfiVerifier._dartFfiLibraryName;
   }
-
-  int? get structPacking {
-    final packedAnnotations =
-        metadata.where((annotation) => annotation.isPacked);
-
-    if (packedAnnotations.isEmpty) {
-      return null;
-    }
-
-    return packedAnnotations.first.packedMemberAlignment;
-  }
 }
 
 extension on ExtensionElement {
@@ -1533,16 +1492,6 @@ extension on DartType {
     return dimensions;
   }
 
-  DartType get arrayElementType {
-    DartType iterator = this;
-    while (iterator is InterfaceType &&
-        iterator.element.name == FfiVerifier._arrayClassName &&
-        iterator.element.isFfiClass) {
-      iterator = iterator.typeArguments.single;
-    }
-    return iterator;
-  }
-
   bool get isAbiSpecificInteger {
     final self = this;
     if (self is InterfaceType) {

pkg/analyzer/messages.yaml

@@ -17172,91 +17172,6 @@ FfiCode:
         external Pointer<Uint8> notEmpty;
       }
       ```
-  PACKED_NESTING_NON_PACKED:
-    problemMessage: "Nesting the non-packed or less tightly packed struct '{0}' in a packed struct '{1}' isn't supported."
-    correctionMessage: Try packing the nested struct or packing the nested struct more tightly.
-    comment: |-
-      Parameters:
-      0: the name of the outer struct
-      1: the name of the struct being nested
-    hasPublishedDocs: true
-    documentation: |-
-      #### Description
-
-      The analyzer produces this diagnostic when a subclass of `Struct` that is
-      annotated as being `Packed` declares a field whose type is also a subclass
-      of `Struct` and the field's type is either not packed or is packed less
-      tightly.
-
-      For more information about FFI, see [C interop using dart:ffi][ffi].
-
-      #### Example
-
-      The following code produces this diagnostic because the class `Outer`,
-      which is a subclass of `Struct` and is packed on 1-byte boundaries,
-      declared a field whose type (`Inner`) is packed on 8-byte boundaries:
-
-      ```dart
-      import 'dart:ffi';
-
-      @Packed(8)
-      class Inner extends Struct {
-        external Pointer<Uint8> notEmpty;
-      }
-
-      @Packed(1)
-      class Outer extends Struct {
-        external Pointer<Uint8> notEmpty;
-
-        external [!Inner!] nestedLooselyPacked;
-      }
-      ```
-
-      #### Common fixes
-
-      If the inner struct should be packed more tightly, then change the
-      argument to the inner struct's `Packed` annotation:
-
-      ```dart
-      import 'dart:ffi';
-
-      @Packed(1)
-      class Inner extends Struct {
-        external Pointer<Uint8> notEmpty;
-      }
-
-      @Packed(1)
-      class Outer extends Struct {
-        external Pointer<Uint8> notEmpty;
-
-        external Inner nestedLooselyPacked;
-      }
-      ```
-
-      If the outer struct should be packed less tightly, then change the
-      argument to the outer struct's `Packed` annotation:
-
-      ```dart
-      import 'dart:ffi';
-
-      @Packed(8)
-      class Inner extends Struct {
-        external Pointer<Uint8> notEmpty;
-      }
-
-      @Packed(8)
-      class Outer extends Struct {
-        external Pointer<Uint8> notEmpty;
-
-        external Inner nestedLooselyPacked;
-      }
-      ```
-
-      If the inner struct doesn't have an annotation and should be packed, then
-      add an annotation.
-
-      If the inner struct doesn't have an annotation and the outer struct
-      shouldn't be packed, then remove its annotation.
   SIZE_ANNOTATION_DIMENSIONS:
     problemMessage: "'Array's must have an 'Array' annotation that matches the dimensions."
     correctionMessage: "Try adjusting the arguments in the 'Array' annotation."

pkg/analyzer/test/src/diagnostics/packed_nesting_non_packed_test.dart

@@ -588,7 +588,6 @@ import 'override_on_non_overriding_setter_test.dart'
     as override_on_non_overriding_setter;
 import 'packed_annotation_alignment_test.dart' as packed_annotation_alignment;
 import 'packed_annotation_test.dart' as packed_annotation;
-import 'packed_nesting_non_packed_test.dart' as packed_nesting_non_packed;
 import 'part_of_different_library_test.dart' as part_of_different_library;
 import 'part_of_non_part_test.dart' as part_of_non_part;
 import 'positional_super_formal_parameter_with_positional_argument_test.dart'
@@ -1184,7 +1183,6 @@ main() {
     override_on_non_overriding_setter.main();
     packed_annotation.main();
     packed_annotation_alignment.main();
-    packed_nesting_non_packed.main();
     part_of_different_library.main();
     part_of_non_part.main();
     positional_super_formal_parameter_with_positional_argument.main();