[analyzer/ffi] Support Unions

This CL does not add unions to `dart:ffi` yet, only to the mock
SDK in the analyzer for testing the analyzer. This means we can review
and land it separately.

Also, this CL fixes some tests to not use nullable fields in Structs.

Bug: #38491

Change-Id: Ia972f31475859aa57e012adf39b636919995b183
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/194788
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

Author: dcharkes

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

@@ -52,7 +52,8 @@ class FfiCode extends AnalyzerErrorCode {
    */
   static const FfiCode FIELD_IN_STRUCT_WITH_INITIALIZER = FfiCode(
       name: 'FIELD_IN_STRUCT_WITH_INITIALIZER',
-      message: "Fields in subclasses of 'Struct' can't have initializers.",
+      message:
+          "Fields in subclasses of 'Struct' and 'Union' can't have initializers.",
       correction:
           "Try removing the initializer and marking the field as external.");
 
@@ -61,7 +62,8 @@ class FfiCode extends AnalyzerErrorCode {
    */
   static const FfiCode FIELD_INITIALIZER_IN_STRUCT = FfiCode(
       name: 'FIELD_INITIALIZER_IN_STRUCT',
-      message: "Constructors in subclasses of 'Struct' can't have field "
+      message:
+          "Constructors in subclasses of 'Struct' and 'Union' can't have field "
           "initializers.",
       correction: "Try removing the field initializer and marking the field as"
           " external.");
@@ -72,7 +74,8 @@ class FfiCode extends AnalyzerErrorCode {
    */
   static const FfiCode GENERIC_STRUCT_SUBCLASS = FfiCode(
       name: 'GENERIC_STRUCT_SUBCLASS',
-      message: "The class '{0}' can't extend 'Struct' because it is generic.",
+      message:
+          "The class '{0}' can't extend 'Struct' or 'Union' because it is generic.",
       correction: "Try removing the type parameters from '{0}'.");
 
   /**
@@ -95,10 +98,10 @@ class FfiCode extends AnalyzerErrorCode {
       message:
           "Fields in struct classes can't have the type '{0}'. They can only "
           "be declared as 'int', 'double', 'Array', 'Pointer', or subtype of "
-          "'Struct'.",
+          "'Struct' or 'Union'.",
       correction:
           "Try using 'int', 'double', 'Array', 'Pointer', or subtype of "
-          "'Struct'.");
+          "'Struct' or 'Union'.");
 
   /**
    * No parameters.
@@ -202,9 +205,9 @@ class FfiCode extends AnalyzerErrorCode {
       message:
           "Type arguments to '{0}' can't have the type '{1}'. They can only "
           "be declared as native integer, 'Float', 'Double', 'Pointer', or "
-          "subtype of Struct'.",
+          "subtype of 'Struct' or 'Union'.",
       correction: "Try using a native integer, 'Float', 'Double', 'Pointer', "
-          "or subtype of 'Struct'.");
+          "or subtype of 'Struct' or 'Union'.");
 
   /**
    * No parameters.
@@ -252,7 +255,7 @@ class FfiCode extends AnalyzerErrorCode {
   static const FfiCode SUBTYPE_OF_FFI_CLASS_IN_EXTENDS = FfiCode(
     name: 'SUBTYPE_OF_FFI_CLASS',
     message: "The class '{0}' can't extend '{1}'.",
-    correction: "Try extending 'Struct'.",
+    correction: "Try extending 'Struct' or 'Union'.",
     uniqueName: 'SUBTYPE_OF_FFI_CLASS_IN_EXTENDS',
   );
 
@@ -264,7 +267,7 @@ class FfiCode extends AnalyzerErrorCode {
   static const FfiCode SUBTYPE_OF_FFI_CLASS_IN_IMPLEMENTS = FfiCode(
     name: 'SUBTYPE_OF_FFI_CLASS',
     message: "The class '{0}' can't implement '{1}'.",
-    correction: "Try extending 'Struct'.",
+    correction: "Try extending 'Struct' or 'Union'.",
     uniqueName: 'SUBTYPE_OF_FFI_CLASS_IN_IMPLEMENTS',
   );
 
@@ -276,7 +279,7 @@ class FfiCode extends AnalyzerErrorCode {
   static const FfiCode SUBTYPE_OF_FFI_CLASS_IN_WITH = FfiCode(
     name: 'SUBTYPE_OF_FFI_CLASS',
     message: "The class '{0}' can't mix in '{1}'.",
-    correction: "Try extending 'Struct'.",
+    correction: "Try extending 'Struct' or 'Union'.",
     uniqueName: 'SUBTYPE_OF_FFI_CLASS_IN_WITH',
   );
 
@@ -288,8 +291,8 @@ class FfiCode extends AnalyzerErrorCode {
   static const FfiCode SUBTYPE_OF_STRUCT_CLASS_IN_EXTENDS = FfiCode(
     name: 'SUBTYPE_OF_STRUCT_CLASS',
     message: "The class '{0}' can't extend '{1}' because '{1}' is a subtype of "
-        "'Struct'.",
-    correction: "Try extending 'Struct' directly.",
+        "'Struct' or 'Union'.",
+    correction: "Try extending 'Struct' or 'Union' directly.",
     uniqueName: 'SUBTYPE_OF_STRUCT_CLASS_IN_EXTENDS',
   );
 
@@ -302,8 +305,8 @@ class FfiCode extends AnalyzerErrorCode {
     name: 'SUBTYPE_OF_STRUCT_CLASS',
     message:
         "The class '{0}' can't implement '{1}' because '{1}' is a subtype of "
-        "'Struct'.",
-    correction: "Try extending 'Struct' directly.",
+        "'Struct' or 'Union'.",
+    correction: "Try extending 'Struct' or 'Union' directly.",
     uniqueName: 'SUBTYPE_OF_STRUCT_CLASS_IN_IMPLEMENTS',
   );
 
@@ -315,8 +318,8 @@ class FfiCode extends AnalyzerErrorCode {
   static const FfiCode SUBTYPE_OF_STRUCT_CLASS_IN_WITH = FfiCode(
     name: 'SUBTYPE_OF_STRUCT_CLASS',
     message: "The class '{0}' can't mix in '{1}' because '{1}' is a subtype of "
-        "'Struct'.",
-    correction: "Try extending 'Struct' directly.",
+        "'Struct' or 'Union'.",
+    correction: "Try extending 'Struct' or 'Union' directly.",
     uniqueName: 'SUBTYPE_OF_STRUCT_CLASS_IN_WITH',
   );
 

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

@@ -41,6 +41,8 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
 
   static const _structClassName = 'Struct';
 
+  static const _unionClassName = 'Union';
+
   /// The type system used to check types.
   final TypeSystemImpl typeSystem;
 
@@ -49,41 +51,43 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
 
   /// A flag indicating whether we are currently visiting inside a subclass of
   /// `Struct`.
-  bool inStruct = false;
+  bool inCompound = false;
 
-  /// Subclass of `Struct` we are currently visiting, or `null`.
-  ClassDeclaration? struct;
+  /// Subclass of `Struct` or `Union` we are currently visiting, or `null`.
+  ClassDeclaration? compound;
 
   /// Initialize a newly created verifier.
   FfiVerifier(this.typeSystem, this._errorReporter);
 
   @override
   void visitClassDeclaration(ClassDeclaration node) {
-    inStruct = false;
-    struct = null;
+    inCompound = false;
+    compound = null;
     // Only the Allocator, Opaque and Struct class may be extended.
     var extendsClause = node.extendsClause;
     if (extendsClause != null) {
       final TypeName superclass = extendsClause.superclass;
       final ffiClass = superclass.ffiClass;
       if (ffiClass != null) {
         final className = ffiClass.name;
-        if (className == _structClassName) {
-          inStruct = true;
-          struct = node;
+        if (className == _structClassName || className == _unionClassName) {
+          inCompound = true;
+          compound = node;
           if (node.declaredElement!.isEmptyStruct) {
             _errorReporter
                 .reportErrorForNode(FfiCode.EMPTY_STRUCT, node, [node.name]);
           }
-          _validatePackedAnnotation(node.metadata);
+          if (className == _structClassName) {
+            _validatePackedAnnotation(node.metadata);
+          }
         } else if (className != _allocatorClassName &&
             className != _opaqueClassName) {
           _errorReporter.reportErrorForNode(
               FfiCode.SUBTYPE_OF_FFI_CLASS_IN_EXTENDS,
               superclass.name,
               [node.name.name, superclass.name.name]);
         }
-      } else if (superclass.isStructSubtype) {
+      } else if (superclass.isCompoundSubtype) {
         _errorReporter.reportErrorForNode(
             FfiCode.SUBTYPE_OF_STRUCT_CLASS_IN_EXTENDS,
             superclass,
@@ -101,7 +105,7 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
       if (typename.ffiClass != null) {
         _errorReporter.reportErrorForNode(
             subtypeOfFfiCode, typename, [node.name, typename.name]);
-      } else if (typename.isStructSubtype) {
+      } else if (typename.isCompoundSubtype) {
         _errorReporter.reportErrorForNode(
             subtypeOfStructCode, typename, [node.name, typename.name]);
       }
@@ -122,7 +126,7 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
       }
     }
 
-    if (inStruct && node.declaredElement!.typeParameters.isNotEmpty) {
+    if (inCompound && node.declaredElement!.typeParameters.isNotEmpty) {
       _errorReporter.reportErrorForNode(
           FfiCode.GENERIC_STRUCT_SUBCLASS, node.name, [node.name]);
     }
@@ -131,7 +135,7 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
 
   @override
   void visitConstructorFieldInitializer(ConstructorFieldInitializer node) {
-    if (inStruct) {
+    if (inCompound) {
       _errorReporter.reportErrorForNode(
           FfiCode.FIELD_INITIALIZER_IN_STRUCT, node);
     }
@@ -140,8 +144,8 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
 
   @override
   void visitFieldDeclaration(FieldDeclaration node) {
-    if (inStruct) {
-      _validateFieldsInStruct(node);
+    if (inCompound) {
+      _validateFieldsInCompound(node);
     }
     super.visitFieldDeclaration(node);
   }
@@ -248,7 +252,7 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
       case _PrimitiveDartType.none:
         break;
     }
-    if (nativeType.isStructSubtype) {
+    if (nativeType.isCompoundSubtype) {
       return true;
     }
     if (nativeType.isPointer) {
@@ -311,10 +315,10 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
         final nativeArgumentType = nativeType.typeArguments.single;
         return _isValidFfiNativeType(nativeArgumentType,
                 allowVoid: true, allowEmptyStruct: true, allowHandle: true) ||
-            nativeArgumentType.isStructSubtype ||
+            nativeArgumentType.isCompoundSubtype ||
             nativeArgumentType.isNativeType;
       }
-      if (nativeType.isStructSubtype) {
+      if (nativeType.isCompoundSubtype) {
         if (!allowEmptyStruct) {
           if (nativeType.element.isEmptyStruct) {
             // TODO(dartbug.com/36780): This results in an error message not
@@ -548,8 +552,8 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
   }
 
   /// Validate that the fields declared by the given [node] meet the
-  /// requirements for fields within a struct class.
-  void _validateFieldsInStruct(FieldDeclaration node) {
+  /// requirements for fields within a struct or union class.
+  void _validateFieldsInCompound(FieldDeclaration node) {
     if (node.isStatic) {
       return;
     }
@@ -576,18 +580,18 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
         final arrayDimensions = declaredType.arrayDimensions;
         _validateSizeOfAnnotation(fieldType, annotations, arrayDimensions);
         final arrayElement = declaredType.arrayElementType;
-        if (arrayElement.isStructSubtype) {
+        if (arrayElement.isCompoundSubtype) {
           final elementClass = (arrayElement as InterfaceType).element;
-          _validatePackingNesting(struct!.declaredElement!, elementClass,
+          _validatePackingNesting(compound!.declaredElement!, elementClass,
               errorNode: fieldType);
         }
-      } else if (declaredType.isStructSubtype) {
+      } else if (declaredType.isCompoundSubtype) {
         final clazz = (declaredType as InterfaceType).element;
         if (clazz.isEmptyStruct) {
           _errorReporter
               .reportErrorForNode(FfiCode.EMPTY_STRUCT, node, [clazz.name]);
         }
-        _validatePackingNesting(struct!.declaredElement!, clazz,
+        _validatePackingNesting(compound!.declaredElement!, clazz,
             errorNode: fieldType);
       } else {
         _errorReporter.reportErrorForNode(FfiCode.INVALID_FIELD_TYPE_IN_STRUCT,
@@ -632,7 +636,7 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
     if ((FT as FunctionType).returnType.isVoid ||
         R.isPointer ||
         R.isHandle ||
-        R.isStructSubtype) {
+        R.isCompoundSubtype) {
       if (argCount != 1) {
         _errorReporter.reportErrorForNode(
             FfiCode.INVALID_EXCEPTION_VALUE, node.argumentList.arguments[1]);
@@ -975,7 +979,7 @@ extension on ClassElement {
         return false;
       } else if (declaredType.isPointer) {
         return false;
-      } else if (declaredType.isStructSubtype) {
+      } else if (declaredType.isCompoundSubtype) {
         return false;
       } else if (declaredType.isArray) {
         return false;
@@ -1087,22 +1091,25 @@ extension on DartType {
     return false;
   }
 
-  bool get isStruct {
+  bool get isCompound {
     final self = this;
     if (self is InterfaceType) {
       final element = self.element;
-      return element.name == FfiVerifier._structClassName && element.isFfiClass;
+      final name = element.name;
+      return (name == FfiVerifier._structClassName ||
+              name == FfiVerifier._unionClassName) &&
+          element.isFfiClass;
     }
     return false;
   }
 
   /// Returns `true` if this is a struct type, i.e. a subtype of `Struct`.
-  bool get isStructSubtype {
+  bool get isCompoundSubtype {
     final self = this;
     if (self is InterfaceType) {
       final superType = self.element.supertype;
       if (superType != null) {
-        return superType.isStruct;
+        return superType.isCompound;
       }
     }
     return false;
@@ -1115,17 +1122,17 @@ extension on TypeName {
     return name.staticElement.ffiClass;
   }
 
-  /// Return `true` if this represents a subtype of `Struct`.
-  bool get isStructSubtype {
+  /// Return `true` if this represents a subtype of `Struct` or `Union`.
+  bool get isCompoundSubtype {
     var element = name.staticElement;
     if (element is ClassElement) {
-      bool isStruct(InterfaceType? type) {
-        return type != null && type.isStruct;
+      bool isCompound(InterfaceType? type) {
+        return type != null && type.isCompound;
       }
 
-      return isStruct(element.supertype) ||
-          element.interfaces.any(isStruct) ||
-          element.mixins.any(isStruct);
+      return isCompound(element.supertype) ||
+          element.interfaces.any(isCompound) ||
+          element.mixins.any(isCompound);
     }
     return false;
   }

pkg/analyzer/lib/src/test_utilities/mock_sdk.dart

@@ -670,12 +670,18 @@ class Pointer<T extends NativeType> extends NativeType {
       [Object exceptionalReturn]) {}
 }
 
+final Pointer<Never> nullptr = Pointer.fromAddress(0);
+
 extension NativeFunctionPointer<NF extends Function>
     on Pointer<NativeFunction<NF>> {
   external DF asFunction<DF extends Function>();
 }
 
-class Struct extends NativeType {}
+class _Compound extends NativeType {}
+
+class Struct extends _Compound {}
+
+class Union extends _Compound {}
 
 class Packed {
   final int memberAlignment;

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

@@ -19,10 +19,21 @@ class FieldInStructWithInitializerTest extends PubPackageResolutionTest {
     await assertErrorsInCode(r'''
 import 'dart:ffi';
 class C extends Struct {
-  Pointer? p = null;
+  Pointer p = nullptr;
 }
 ''', [
-      error(FfiCode.FIELD_IN_STRUCT_WITH_INITIALIZER, 55, 1),
+      error(FfiCode.FIELD_IN_STRUCT_WITH_INITIALIZER, 54, 1),
+    ]);
+  }
+
+  test_instance_withInitializer2() async {
+    await assertErrorsInCode(r'''
+import 'dart:ffi';
+class C extends Union {
+  Pointer p = nullptr;
+}
+''', [
+      error(FfiCode.FIELD_IN_STRUCT_WITH_INITIALIZER, 53, 1),
     ]);
   }