[vm/ffi] Support @Native fields

Allow annotating top-level or static fields with `@Native` to create
fields backed by native memory.
By using the `_addressOf` operator implemented in the VM, these fields
can be implemented in the CFE by replacing them with accessors looking
up the pointer and then using existing methods to load and store the
value.

Closes #50551

TEST=tests/ffi/native_assets/asset_*_test.dart
TEST=pkg/analyzer/test/src/diagnostics/ffi_native_test.dart

CoreLibraryReviewExempt: VM & dart2wasm only feature
Change-Id: I61dccc88076723d6a6ba02d7fd848b18e4caf780
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/338020
Reviewed-by: Daco Harkes <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Reviewed-by: Lasse Nielsen <[email protected]>
Reviewed-by: Chloe Stefantsova <[email protected]>

Author: simolus3

CHANGELOG.md

@@ -51,6 +51,12 @@
 - `String.fromCharCodes` now allow `start` and `end` to be after the end of
   the `Iterable` argument, just like `skip` and `take` does on an `Iterable`.
 
+#### `dart:ffi`
+
+- In addition to functions, `@Native` can now be used on fields.
+- Allow taking the address of native functions and fields via
+  `Native.addressOf`.
+
 #### `dart:nativewrappers`
 
 - **Breaking Change** [#51896][]: The NativeWrapperClasses are marked `base` so

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

@@ -5275,15 +5275,47 @@ const MessageCode messageFfiNativeDuplicateAnnotations = const MessageCode(
     "FfiNativeDuplicateAnnotations",
     analyzerCodes: <String>["FFI_NATIVE_INVALID_MULTIPLE_ANNOTATIONS"],
     problemMessage:
-        r"""Native functions must not have more than @Native annotation.""");
+        r"""Native functions and fields must not have more than @Native annotation.""");
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeFfiNativeFieldMissingType =
+    messageFfiNativeFieldMissingType;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageFfiNativeFieldMissingType = const MessageCode(
+    "FfiNativeFieldMissingType",
+    analyzerCodes: <String>["NATIVE_FIELD_MISSING_TYPE"],
+    problemMessage:
+        r"""The native type of this field could not be inferred and must be specified in the annotation.""");
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeFfiNativeFieldMustBeStatic =
+    messageFfiNativeFieldMustBeStatic;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageFfiNativeFieldMustBeStatic = const MessageCode(
+    "FfiNativeFieldMustBeStatic",
+    analyzerCodes: <String>["NATIVE_FIELD_NOT_STATIC"],
+    problemMessage: r"""Native fields must be static.""");
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeFfiNativeFieldType = messageFfiNativeFieldType;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageFfiNativeFieldType = const MessageCode(
+    "FfiNativeFieldType",
+    analyzerCodes: <String>["NATIVE_FIELD_INVALID_TYPE"],
+    problemMessage:
+        r"""Unsupported type for native fields. Native fields only support pointers, compounds and numeric types.""");
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Code<Null> codeFfiNativeMustBeExternal = messageFfiNativeMustBeExternal;
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const MessageCode messageFfiNativeMustBeExternal = const MessageCode(
     "FfiNativeMustBeExternal",
-    problemMessage: r"""Native functions must be marked external.""");
+    problemMessage:
+        r"""Native functions and fields must be marked external.""");
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Code<Null> codeFfiNativeOnlyNativeFieldWrapperClassCanBePointer =

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

@@ -1798,6 +1798,12 @@ FfiCode.MUST_BE_A_SUBTYPE:
   status: noFix
 FfiCode.MUST_RETURN_VOID:
   status: noFix
+FfiCode.NATIVE_FIELD_INVALID_TYPE:
+  status: needsEvaluation
+FfiCode.NATIVE_FIELD_MISSING_TYPE:
+  status: needsEvaluation
+FfiCode.NATIVE_FIELD_NOT_STATIC:
+  status: needsEvaluation
 FfiCode.NON_CONSTANT_TYPE_ARGUMENT:
   status: noFix
 FfiCode.NON_NATIVE_FUNCTION_TYPE_ARGUMENT_TO_POINTER:

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

@@ -87,7 +87,8 @@ class FfiCode extends AnalyzerErrorCode {
   static const FfiCode ARGUMENT_MUST_BE_NATIVE = FfiCode(
     'ARGUMENT_MUST_BE_NATIVE',
     "Argument to 'Native.addressOf' must be annotated with @Native",
-    correctionMessage: "Try passing a static function annotated with '@Native'",
+    correctionMessage:
+        "Try passing a static function or field annotated with '@Native'",
   );
 
   ///  No parameters.
@@ -163,7 +164,7 @@ class FfiCode extends AnalyzerErrorCode {
   ///  No parameters
   static const FfiCode FFI_NATIVE_INVALID_MULTIPLE_ANNOTATIONS = FfiCode(
     'FFI_NATIVE_INVALID_MULTIPLE_ANNOTATIONS',
-    "Native functions must have exactly one `@Native` annotation.",
+    "Native functions and fields must have exactly one `@Native` annotation.",
     correctionMessage: "Try removing the extra annotation.",
   );
 
@@ -368,6 +369,37 @@ class FfiCode extends AnalyzerErrorCode {
     hasPublishedDocs: true,
   );
 
+  ///  Parameters:
+  ///  0: The invalid type.
+  static const FfiCode NATIVE_FIELD_INVALID_TYPE = FfiCode(
+    'NATIVE_FIELD_INVALID_TYPE',
+    "'{0}' is an unsupported type for native fields. Native fields only "
+        "support pointers or numeric and compound types.",
+    correctionMessage:
+        "Try changing the type in the `@Native` annotation to a numeric FFI "
+        "type, a pointer, or a compound class.",
+    hasPublishedDocs: true,
+  );
+
+  ///  No parameters
+  static const FfiCode NATIVE_FIELD_MISSING_TYPE = FfiCode(
+    'NATIVE_FIELD_MISSING_TYPE',
+    "The native type of this field could not be inferred and must be specified "
+        "in the annotation.",
+    correctionMessage:
+        "Try adding a type parameter extending `NativeType` to the `@Native` "
+        "annotation.",
+    hasPublishedDocs: true,
+  );
+
+  ///  No parameters
+  static const FfiCode NATIVE_FIELD_NOT_STATIC = FfiCode(
+    'NATIVE_FIELD_NOT_STATIC',
+    "Native fields must be static.",
+    correctionMessage: "Try adding the modifier 'static' to this field.",
+    hasPublishedDocs: true,
+  );
+
   ///  Parameters:
   ///  0: the name of the function, method, or constructor having type arguments
   static const FfiCode NON_CONSTANT_TYPE_ARGUMENT = FfiCode(

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

@@ -611,6 +611,9 @@ const List<ErrorCode> errorCodeValues = [
   FfiCode.MUST_BE_A_NATIVE_FUNCTION_TYPE,
   FfiCode.MUST_BE_A_SUBTYPE,
   FfiCode.MUST_RETURN_VOID,
+  FfiCode.NATIVE_FIELD_INVALID_TYPE,
+  FfiCode.NATIVE_FIELD_MISSING_TYPE,
+  FfiCode.NATIVE_FIELD_NOT_STATIC,
   FfiCode.NON_CONSTANT_TYPE_ARGUMENT,
   FfiCode.NON_LEAF_CALL_MUST_NOT_TAKE_TYPED_DATA,
   FfiCode.NON_NATIVE_FUNCTION_TYPE_ARGUMENT_TO_POINTER,