pkgs/ffigen/lib/src/code_generator/writer.dart - native - Git at Google

 // 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.

 import 'package:path/path.dart' as p;

 import '../code_generator.dart';
 import '../context.dart';
 import '../strings.dart' as strings;
 import '../visitor/visitor.dart';
 import 'utils.dart';

 /// To store generated String bindings.
 class Writer {
   final Context context;
   final String? header;

   /// Holds bindings, which lookup symbols.
   final List<Binding> lookUpBindings;

   /// Holds bindings, which lookup symbols through `FfiNative`.
   final List<Binding> ffiNativeBindings;

   /// Holds bindings which don't lookup symbols.
   final List<Binding> noLookUpBindings;

   /// The default asset id to use for [ffiNativeBindings].
   final String? nativeAssetId;

   /// Manages the `_SymbolAddress` class.
   final SymbolAddressWriter symbolAddressWriter;

   final String? classDocComment;

   final bool generateForPackageObjectiveC;

   final List<String> nativeEntryPoints;

   /// Set true after calling [generate]. Indicates if
   /// [generateSymbolOutputYamlMap] can be called.
   bool get canGenerateSymbolOutput => _canGenerateSymbolOutput;
   bool _canGenerateSymbolOutput = false;

   final bool silenceEnumWarning;

   Writer({
     required this.lookUpBindings,
     required this.ffiNativeBindings,
     required this.noLookUpBindings,
     required this.nativeAssetId,
     List<LibraryImport> additionalImports = const <LibraryImport>[],
     this.classDocComment,
     this.header,
     required this.generateForPackageObjectiveC,
     required this.silenceEnumWarning,
     required this.nativeEntryPoints,
     required this.context,
   }) : symbolAddressWriter = SymbolAddressWriter(context);

   /// Writes all bindings to a String.
   String generate() {
     final s = StringBuffer();

     // We write the source first to determine which imports are actually
     // referenced. Headers and [s] are then combined into the final result.
     final result = StringBuffer();

     // Write file header (if any).
     if (header != null) {
       result.writeln(header);
     }

     // Write auto generated declaration.
     result.write(
       makeDoc(
         'AUTO GENERATED FILE, DO NOT EDIT.\n\nGenerated by `package:ffigen`.',
       ),
     );

     // Write lint ignore if not specified by user already.
     if (!RegExp(r'ignore_for_file:\s*type\s*=\s*lint').hasMatch(header ?? '')) {
       result.write(makeDoc('ignore_for_file: type=lint'));
     }

     // If there are any @Native bindings, the file needs to have an
     // `@DefaultAsset` annotation for the symbols to resolve properly. This
     // avoids duplicating the asset on every element.
     // Since the annotation goes on a `library;` directive, it needs to appear
     // before other definitions in the file.
     if (ffiNativeBindings.isNotEmpty && nativeAssetId != null) {
       final ffiPrefix = context.libs.prefix(ffiImport);
       result
         ..writeln("@$ffiPrefix.DefaultAsset('$nativeAssetId')")
         ..writeln('library;\n');
     }

     /// Write [lookUpBindings].
     if (lookUpBindings.isNotEmpty) {
       final ffiPrefix = context.libs.prefix(ffiImport);
       final className = context.extraSymbols.wrapperClassName!.name;
       final lookupFn = context.extraSymbols.lookupFuncName!.name;
       // Write doc comment for wrapper class.
       s.write(makeDartDoc(classDocComment));
       // Write wrapper class.
       s.write('class $className{\n');
       // Write dylib.
       s.write('/// Holds the symbol lookup function.\n');
       s.write(
         'final $ffiPrefix.Pointer<T> Function<T extends '
         '$ffiPrefix.NativeType>(String symbolName) $lookupFn;\n',
       );
       s.write('\n');
       //Write doc comment for wrapper class constructor.
       s.write(makeDartDoc('The symbols are looked up in [dynamicLibrary].'));
       // Write wrapper class constructor.
       s.write(
         '$className($ffiPrefix.DynamicLibrary dynamicLibrary): '
         '$lookupFn = dynamicLibrary.lookup;\n\n',
       );
       //Write doc comment for wrapper class named constructor.
       s.write(makeDartDoc('The symbols are looked up with [lookup].'));
       // Write wrapper class named constructor.
       s.write(
         '$className.fromLookup($ffiPrefix.Pointer<T> '
         'Function<T extends $ffiPrefix.NativeType>('
         'String symbolName) lookup): $lookupFn = lookup;\n\n',
       );
       for (final b in lookUpBindings) {
         s.write(b.toBindingString(this).string);
       }
       if (symbolAddressWriter.shouldGenerate &&
           symbolAddressWriter.hasNonNativeAddress) {
         s.write(symbolAddressWriter.writeObject(this));
       }

       s.write('}\n\n');
     }

     if (ffiNativeBindings.isNotEmpty) {
       for (final b in ffiNativeBindings) {
         s.write(b.toBindingString(this).string);
       }
     }

     if (symbolAddressWriter.shouldGenerate) {
       if (!symbolAddressWriter.hasNonNativeAddress) {
         s.write(symbolAddressWriter.writeObject(this));
       }
       s.write(symbolAddressWriter.writeClass(this));
     }

     /// Write [noLookUpBindings].
     for (final b in noLookUpBindings) {
       s.write(b.toBindingString(this).string);
     }

     // Write neccesary imports.
     final libs = context.libs.used.toList()
       ..sort((l1, l2) => l1.name.compareTo(l2.name));
     for (final lib in libs) {
       final path = lib.importPath(generateForPackageObjectiveC);
       result.write("import '$path' as ${context.libs.prefix(lib)};\n");
     }
     result.write(s);

     // Warn about Enum usage in API surface.
     if (!silenceEnumWarning) {
       final notEnums = _allBindings.where(
         (b) => b is! Type || (b as Type).typealiasType is! EnumClass,
       );
       final usedEnums = visit(context, _FindEnumsVisitation(), notEnums).enums;
       if (usedEnums.isNotEmpty) {
         final names = usedEnums.map((e) => e.originalName).toList()..sort();
         context.logger.severe(
           'The integer type used for enums is '
           'implementation-defined. FFIgen tries to mimic the integer sizes '
           'chosen by the most common compilers for the various OS and '
           'architecture combinations. To prevent any crashes, remove the '
           'enums from your API surface. To rely on the (unsafe!) mimicking, '
           'you can silence this warning by adding silence-enum-warning: true '
           'to the FFIgen config. Affected enums:\n\t${names.join('\n\t')}',
         );
       }
     }

     _canGenerateSymbolOutput = true;
     return result.toString();
   }

   List<Binding> get _allBindings => <Binding>[
     ...noLookUpBindings,
     ...ffiNativeBindings,
     ...lookUpBindings,
   ];

   Map<String, dynamic> generateSymbolOutputYamlMap(String importFilePath) {
     final bindings = _allBindings;
     if (!canGenerateSymbolOutput) {
       throw Exception(
         'Invalid state: generateSymbolOutputYamlMap() '
         'called before generate()',
       );
     }

     // Warn for macros.
     final hasMacroBindings = bindings.any(
       (element) => element is Constant && element.usr.contains('@macro@'),
     );
     if (hasMacroBindings) {
       context.logger.info(
         'Removing all Macros from symbol file since they cannot '
         'be cross referenced reliably.',
       );
     }

     // Remove internal bindings and macros.
     bindings.removeWhere((element) {
       return element.isInternal ||
           (element is Constant && element.usr.contains('@macro@'));
     });

     // Sort bindings alphabetically by USR.
     bindings.sort((a, b) => a.usr.compareTo(b.usr));

     final usesFfiNative = bindings.whereType<Func>().any(
       (element) => element.loadFromNativeAsset,
     );

     return {
       strings.formatVersion: strings.symbolFileFormatVersion,
       strings.files: {
         importFilePath: {
           strings.usedConfig: {strings.ffiNative: usesFfiNative},
           strings.symbols: {
             for (final b in bindings) b.usr: _makeSymbolMapValue(b),
           },
         },
       },
     };
   }

   Map<String, String> _makeSymbolMapValue(Binding b) {
     final dartName = b is Typealias ? getTypedefDartAliasName(b) : null;
     return {
       strings.name: b.name,
       if (dartName != null) strings.dartName: dartName,
     };
   }

   String? getTypedefDartAliasName(Type b) {
     if (b is! Typealias) return null;
     return b.dartAliasName?.name ?? getTypedefDartAliasName(b.type);
   }

   static String _objcImport(String entryPoint, String outDir) {
     final frameworkHeader = parseObjCFrameworkHeader(entryPoint);

     if (frameworkHeader == null) {
       // If it's not a framework header, use a relative import.
       return '#import "${p.relative(entryPoint, from: outDir)}"\n';
     }

     // If it's a framework header, use a <> style import.
     return '#import <$frameworkHeader>\n';
   }

   /// Writes the Objective C code needed for the bindings, if any. Returns null
   /// if there are no bindings that need generated ObjC code. This function does
   /// not generate the output file, but the [outFilename] does affect the
   /// generated code.
   String? generateObjC(String outFilename) {
     final outDir = p.dirname(outFilename);

     final s = StringBuffer();
     s.write('''
 #include <stdint.h>
 #import <Foundation/Foundation.h>
 #import <objc/message.h>
 ''');

     for (final entryPoint in nativeEntryPoints) {
       s.write(_objcImport(entryPoint, outDir));
     }
     s.write(r'''

 #if !__has_feature(objc_arc)
 #error "This file must be compiled with ARC enabled"
 #endif

 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wundeclared-selector"

 typedef struct {
   int64_t version;
   void* (*newWaiter)(void);
   void (*awaitWaiter)(void*);
   void* (*currentIsolate)(void);
   void (*enterIsolate)(void*);
   void (*exitIsolate)(void);
   int64_t (*getMainPortId)(void);
   bool (*getCurrentThreadOwnsIsolate)(int64_t);
 } DOBJC_Context;

 id objc_retainBlock(id);

 #define BLOCKING_BLOCK_IMPL(ctx, BLOCK_SIG, INVOKE_DIRECT, INVOKE_LISTENER)    \
   assert(ctx->version >= 1);                                                   \
   void* targetIsolate = ctx->currentIsolate();                                 \
   int64_t targetPort = ctx->getMainPortId == NULL ? 0 : ctx->getMainPortId();  \
   return BLOCK_SIG {                                                           \
     void* currentIsolate = ctx->currentIsolate();                              \
     bool mayEnterIsolate =                                                     \
         currentIsolate == NULL &&                                              \
         ctx->getCurrentThreadOwnsIsolate != NULL &&                            \
         ctx->getCurrentThreadOwnsIsolate(targetPort);                          \
     if (currentIsolate == targetIsolate || mayEnterIsolate) {                  \
       if (mayEnterIsolate) {                                                   \
         ctx->enterIsolate(targetIsolate);                                      \
       }                                                                        \
       INVOKE_DIRECT;                                                           \
       if (mayEnterIsolate) {                                                   \
         ctx->exitIsolate();                                                    \
       }                                                                        \
     } else {                                                                   \
       void* waiter = ctx->newWaiter();                                         \
       INVOKE_LISTENER;                                                         \
       ctx->awaitWaiter(waiter);                                                \
     }                                                                          \
   };

 ''');

     var empty = true;
     for (final binding in _allBindings) {
       final bindingString = binding.toObjCBindingString(this);
       if (bindingString != null) {
         empty = false;
         s.write(bindingString.string);
       }
     }

     s.write('''
 #undef BLOCKING_BLOCK_IMPL

 #pragma clang diagnostic pop
 ''');

     return empty ? null : s.toString();
   }
 }

 /// Manages the generated `_SymbolAddress` class.
 class SymbolAddressWriter {
   final Context context;
   final List<_SymbolAddressUnit> _addresses = [];

   /// Used to check if we need to generate `_SymbolAddress` class.
   bool get shouldGenerate => _addresses.isNotEmpty;

   bool hasNonNativeAddress = false;

   SymbolAddressWriter(this.context);

   late final _symbolAddressClassName = context.rootScope.addPrivate(
     '_SymbolAddresses',
   );

   void addSymbol({
     required String type,
     required String name,
     required String ptrName,
   }) {
     hasNonNativeAddress = true;
     _addresses.add(_SymbolAddressUnit(type, name, ptrName, false));
   }

   void addNativeSymbol({required String type, required String name}) {
     _addresses.add(_SymbolAddressUnit(type, name, '', true));
   }

   String writeObject(Writer w) {
     final fieldName = context.extraSymbols.symbolAddressVariableName.name;

     if (hasNonNativeAddress) {
       return 'late final $fieldName = $_symbolAddressClassName(this);';
     } else {
       return 'const $fieldName = $_symbolAddressClassName();';
     }
   }

   String writeClass(Writer w) {
     final sb = StringBuffer();
     sb.write('class $_symbolAddressClassName {\n');

     late final libraryVarName = context.rootScope.addPrivate('_library');
     if (hasNonNativeAddress) {
       // Write Library object.
       final wrapperClassName = context.extraSymbols.wrapperClassName!.name;
       sb.write('  final $wrapperClassName $libraryVarName;\n');
       // Write Constructor.
       sb.write('  $_symbolAddressClassName(this.$libraryVarName);\n');
     } else {
       // Native bindings are top-level, so we don't need a field here.
       sb.write('  const $_symbolAddressClassName();');
     }

     for (final address in _addresses) {
       sb.write('  ${address.type} get ${address.name} => ');

       if (address.native) {
         // For native fields and functions, we can use Native.addressOf to look
         // up their address.
         // The name of address getter shadows the actual element in the library,
         // so we need to use a self-import.
         final arg = '${context.libs.prefix(selfImport)}.${address.name}';
         sb.writeln('${context.libs.prefix(ffiImport)}.Native.addressOf($arg);');
       } else {
         // For other elements, the generator will write a private field of type
         // Pointer which we can reference here.
         sb.writeln('$libraryVarName.${address.ptrName};');
       }
     }
     sb.write('}\n');
     return sb.toString();
   }
 }

 /// Holds the data for a single symbol address.
 class _SymbolAddressUnit {
   final String type, name, ptrName;

   /// Whether the symbol we're looking up has been declared with `@Native`.
   final bool native;

   _SymbolAddressUnit(this.type, this.name, this.ptrName, this.native);
 }

 class _FindEnumsVisitation extends Visitation {
   final enums = <EnumClass>{};

   @override
   void visitEnumClass(EnumClass node) {
     node.visitChildren(visitor);
     enums.add(node);
   }
 }
	// 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.

	import 'package:path/path.dart' as p;

	import '../code_generator.dart';
	import '../context.dart';
	import '../strings.dart' as strings;
	import '../visitor/visitor.dart';
	import 'utils.dart';

	/// To store generated String bindings.
	class Writer {
	final Context context;
	final String? header;

	/// Holds bindings, which lookup symbols.
	final List<Binding> lookUpBindings;

	/// Holds bindings, which lookup symbols through `FfiNative`.
	final List<Binding> ffiNativeBindings;

	/// Holds bindings which don't lookup symbols.
	final List<Binding> noLookUpBindings;

	/// The default asset id to use for [ffiNativeBindings].
	final String? nativeAssetId;

	/// Manages the `_SymbolAddress` class.
	final SymbolAddressWriter symbolAddressWriter;

	final String? classDocComment;

	final bool generateForPackageObjectiveC;

	final List<String> nativeEntryPoints;

	/// Set true after calling [generate]. Indicates if
	/// [generateSymbolOutputYamlMap] can be called.
	bool get canGenerateSymbolOutput => _canGenerateSymbolOutput;
	bool _canGenerateSymbolOutput = false;

	final bool silenceEnumWarning;

	Writer({
	required this.lookUpBindings,
	required this.ffiNativeBindings,
	required this.noLookUpBindings,
	required this.nativeAssetId,
	List<LibraryImport> additionalImports = const <LibraryImport>[],
	this.classDocComment,
	this.header,
	required this.generateForPackageObjectiveC,
	required this.silenceEnumWarning,
	required this.nativeEntryPoints,
	required this.context,
	}) : symbolAddressWriter = SymbolAddressWriter(context);

	/// Writes all bindings to a String.
	String generate() {
	final s = StringBuffer();

	// We write the source first to determine which imports are actually
	// referenced. Headers and [s] are then combined into the final result.
	final result = StringBuffer();

	// Write file header (if any).
	if (header != null) {
	result.writeln(header);
	}

	// Write auto generated declaration.
	result.write(
	makeDoc(
	'AUTO GENERATED FILE, DO NOT EDIT.\n\nGenerated by `package:ffigen`.',
	),
	);

	// Write lint ignore if not specified by user already.
	if (!RegExp(r'ignore_for_file:\stype\s=\s*lint').hasMatch(header ?? '')) {
	result.write(makeDoc('ignore_for_file: type=lint'));
	}

	// If there are any @Native bindings, the file needs to have an
	// `@DefaultAsset` annotation for the symbols to resolve properly. This
	// avoids duplicating the asset on every element.
	// Since the annotation goes on a `library;` directive, it needs to appear
	// before other definitions in the file.
	if (ffiNativeBindings.isNotEmpty && nativeAssetId != null) {
	final ffiPrefix = context.libs.prefix(ffiImport);
	result
	..writeln("@$ffiPrefix.DefaultAsset('$nativeAssetId')")
	..writeln('library;\n');
	}

	/// Write [lookUpBindings].
	if (lookUpBindings.isNotEmpty) {
	final ffiPrefix = context.libs.prefix(ffiImport);
	final className = context.extraSymbols.wrapperClassName!.name;
	final lookupFn = context.extraSymbols.lookupFuncName!.name;
	// Write doc comment for wrapper class.
	s.write(makeDartDoc(classDocComment));
	// Write wrapper class.
	s.write('class $className{\n');
	// Write dylib.
	s.write('/// Holds the symbol lookup function.\n');
	s.write(
	'final $ffiPrefix.Pointer<T> Function<T extends '
	'$ffiPrefix.NativeType>(String symbolName) $lookupFn;\n',
	);
	s.write('\n');
	//Write doc comment for wrapper class constructor.
	s.write(makeDartDoc('The symbols are looked up in [dynamicLibrary].'));
	// Write wrapper class constructor.
	s.write(
	'$className($ffiPrefix.DynamicLibrary dynamicLibrary): '
	'$lookupFn = dynamicLibrary.lookup;\n\n',
	);
	//Write doc comment for wrapper class named constructor.
	s.write(makeDartDoc('The symbols are looked up with [lookup].'));
	// Write wrapper class named constructor.
	s.write(
	'$className.fromLookup($ffiPrefix.Pointer<T> '
	'Function<T extends $ffiPrefix.NativeType>('
	'String symbolName) lookup): $lookupFn = lookup;\n\n',
	);
	for (final b in lookUpBindings) {
	s.write(b.toBindingString(this).string);
	}
	if (symbolAddressWriter.shouldGenerate &&
	symbolAddressWriter.hasNonNativeAddress) {
	s.write(symbolAddressWriter.writeObject(this));
	}

	s.write('}\n\n');
	}

	if (ffiNativeBindings.isNotEmpty) {
	for (final b in ffiNativeBindings) {
	s.write(b.toBindingString(this).string);
	}
	}

	if (symbolAddressWriter.shouldGenerate) {
	if (!symbolAddressWriter.hasNonNativeAddress) {
	s.write(symbolAddressWriter.writeObject(this));
	}
	s.write(symbolAddressWriter.writeClass(this));
	}

	/// Write [noLookUpBindings].
	for (final b in noLookUpBindings) {
	s.write(b.toBindingString(this).string);
	}

	// Write neccesary imports.
	final libs = context.libs.used.toList()
	..sort((l1, l2) => l1.name.compareTo(l2.name));
	for (final lib in libs) {
	final path = lib.importPath(generateForPackageObjectiveC);
	result.write("import '$path' as ${context.libs.prefix(lib)};\n");
	}
	result.write(s);

	// Warn about Enum usage in API surface.
	if (!silenceEnumWarning) {
	final notEnums = _allBindings.where(
	(b) => b is! Type \|\| (b as Type).typealiasType is! EnumClass,
	);
	final usedEnums = visit(context, _FindEnumsVisitation(), notEnums).enums;
	if (usedEnums.isNotEmpty) {
	final names = usedEnums.map((e) => e.originalName).toList()..sort();
	context.logger.severe(
	'The integer type used for enums is '
	'implementation-defined. FFIgen tries to mimic the integer sizes '
	'chosen by the most common compilers for the various OS and '
	'architecture combinations. To prevent any crashes, remove the '
	'enums from your API surface. To rely on the (unsafe!) mimicking, '
	'you can silence this warning by adding silence-enum-warning: true '
	'to the FFIgen config. Affected enums:\n\t${names.join('\n\t')}',
	);
	}
	}

	_canGenerateSymbolOutput = true;
	return result.toString();
	}

	List<Binding> get _allBindings => <Binding>[
	...noLookUpBindings,
	...ffiNativeBindings,
	...lookUpBindings,
	];

	Map<String, dynamic> generateSymbolOutputYamlMap(String importFilePath) {
	final bindings = _allBindings;
	if (!canGenerateSymbolOutput) {
	throw Exception(
	'Invalid state: generateSymbolOutputYamlMap() '
	'called before generate()',
	);
	}

	// Warn for macros.
	final hasMacroBindings = bindings.any(
	(element) => element is Constant && element.usr.contains('@macro@'),
	);
	if (hasMacroBindings) {
	context.logger.info(
	'Removing all Macros from symbol file since they cannot '
	'be cross referenced reliably.',
	);
	}

	// Remove internal bindings and macros.
	bindings.removeWhere((element) {
	return element.isInternal \|\|
	(element is Constant && element.usr.contains('@macro@'));
	});

	// Sort bindings alphabetically by USR.
	bindings.sort((a, b) => a.usr.compareTo(b.usr));

	final usesFfiNative = bindings.whereType<Func>().any(
	(element) => element.loadFromNativeAsset,
	);

	return {
	strings.formatVersion: strings.symbolFileFormatVersion,
	strings.files: {
	importFilePath: {
	strings.usedConfig: {strings.ffiNative: usesFfiNative},
	strings.symbols: {
	for (final b in bindings) b.usr: _makeSymbolMapValue(b),
	},
	},
	},
	};
	}

	Map<String, String> _makeSymbolMapValue(Binding b) {
	final dartName = b is Typealias ? getTypedefDartAliasName(b) : null;
	return {
	strings.name: b.name,
	if (dartName != null) strings.dartName: dartName,
	};
	}

	String? getTypedefDartAliasName(Type b) {
	if (b is! Typealias) return null;
	return b.dartAliasName?.name ?? getTypedefDartAliasName(b.type);
	}

	static String _objcImport(String entryPoint, String outDir) {
	final frameworkHeader = parseObjCFrameworkHeader(entryPoint);

	if (frameworkHeader == null) {
	// If it's not a framework header, use a relative import.
	return '#import "${p.relative(entryPoint, from: outDir)}"\n';
	}

	// If it's a framework header, use a <> style import.
	return '#import <$frameworkHeader>\n';
	}

	/// Writes the Objective C code needed for the bindings, if any. Returns null
	/// if there are no bindings that need generated ObjC code. This function does
	/// not generate the output file, but the [outFilename] does affect the
	/// generated code.
	String? generateObjC(String outFilename) {
	final outDir = p.dirname(outFilename);

	final s = StringBuffer();
	s.write('''
	#include <stdint.h>
	#import <Foundation/Foundation.h>
	#import <objc/message.h>
	''');

	for (final entryPoint in nativeEntryPoints) {
	s.write(_objcImport(entryPoint, outDir));
	}
	s.write(r'''

	#if !__has_feature(objc_arc)
	#error "This file must be compiled with ARC enabled"
	#endif

	#pragma clang diagnostic push
	#pragma clang diagnostic ignored "-Wundeclared-selector"

	typedef struct {
	int64_t version;
	void* (*newWaiter)(void);
	void (awaitWaiter)(void);
	void* (*currentIsolate)(void);
	void (enterIsolate)(void);
	void (*exitIsolate)(void);
	int64_t (*getMainPortId)(void);
	bool (*getCurrentThreadOwnsIsolate)(int64_t);
	} DOBJC_Context;

	id objc_retainBlock(id);

	#define BLOCKING_BLOCK_IMPL(ctx, BLOCK_SIG, INVOKE_DIRECT, INVOKE_LISTENER) \
	assert(ctx->version >= 1); \
	void* targetIsolate = ctx->currentIsolate(); \
	int64_t targetPort = ctx->getMainPortId == NULL ? 0 : ctx->getMainPortId(); \
	return BLOCK_SIG { \
	void* currentIsolate = ctx->currentIsolate(); \
	bool mayEnterIsolate = \
	currentIsolate == NULL && \
	ctx->getCurrentThreadOwnsIsolate != NULL && \
	ctx->getCurrentThreadOwnsIsolate(targetPort); \
	if (currentIsolate == targetIsolate \|\| mayEnterIsolate) { \
	if (mayEnterIsolate) { \
	ctx->enterIsolate(targetIsolate); \
	} \
	INVOKE_DIRECT; \
	if (mayEnterIsolate) { \
	ctx->exitIsolate(); \
	} \
	} else { \
	void* waiter = ctx->newWaiter(); \
	INVOKE_LISTENER; \
	ctx->awaitWaiter(waiter); \
	} \
	};

	''');

	var empty = true;
	for (final binding in _allBindings) {
	final bindingString = binding.toObjCBindingString(this);
	if (bindingString != null) {
	empty = false;
	s.write(bindingString.string);
	}
	}

	s.write('''
	#undef BLOCKING_BLOCK_IMPL

	#pragma clang diagnostic pop
	''');

	return empty ? null : s.toString();
	}
	}

	/// Manages the generated `_SymbolAddress` class.
	class SymbolAddressWriter {
	final Context context;
	final List<_SymbolAddressUnit> _addresses = [];

	/// Used to check if we need to generate `_SymbolAddress` class.
	bool get shouldGenerate => _addresses.isNotEmpty;

	bool hasNonNativeAddress = false;

	SymbolAddressWriter(this.context);

	late final _symbolAddressClassName = context.rootScope.addPrivate(
	'_SymbolAddresses',
	);

	void addSymbol({
	required String type,
	required String name,
	required String ptrName,
	}) {
	hasNonNativeAddress = true;
	_addresses.add(_SymbolAddressUnit(type, name, ptrName, false));
	}

	void addNativeSymbol({required String type, required String name}) {
	_addresses.add(_SymbolAddressUnit(type, name, '', true));
	}

	String writeObject(Writer w) {
	final fieldName = context.extraSymbols.symbolAddressVariableName.name;

	if (hasNonNativeAddress) {
	return 'late final $fieldName = $_symbolAddressClassName(this);';
	} else {
	return 'const $fieldName = $_symbolAddressClassName();';
	}
	}

	String writeClass(Writer w) {
	final sb = StringBuffer();
	sb.write('class $_symbolAddressClassName {\n');

	late final libraryVarName = context.rootScope.addPrivate('_library');
	if (hasNonNativeAddress) {
	// Write Library object.
	final wrapperClassName = context.extraSymbols.wrapperClassName!.name;
	sb.write(' final $wrapperClassName $libraryVarName;\n');
	// Write Constructor.
	sb.write(' $_symbolAddressClassName(this.$libraryVarName);\n');
	} else {
	// Native bindings are top-level, so we don't need a field here.
	sb.write(' const $_symbolAddressClassName();');
	}

	for (final address in _addresses) {
	sb.write(' ${address.type} get ${address.name} => ');

	if (address.native) {
	// For native fields and functions, we can use Native.addressOf to look
	// up their address.
	// The name of address getter shadows the actual element in the library,
	// so we need to use a self-import.
	final arg = '${context.libs.prefix(selfImport)}.${address.name}';
	sb.writeln('${context.libs.prefix(ffiImport)}.Native.addressOf($arg);');
	} else {
	// For other elements, the generator will write a private field of type
	// Pointer which we can reference here.
	sb.writeln('$libraryVarName.${address.ptrName};');
	}
	}
	sb.write('}\n');
	return sb.toString();
	}
	}

	/// Holds the data for a single symbol address.
	class _SymbolAddressUnit {
	final String type, name, ptrName;

	/// Whether the symbol we're looking up has been declared with `@Native`.
	final bool native;

	_SymbolAddressUnit(this.type, this.name, this.ptrName, this.native);
	}

	class _FindEnumsVisitation extends Visitation {
	final enums = <EnumClass>{};

	@override
	void visitEnumClass(EnumClass node) {
	node.visitChildren(visitor);
	enums.add(node);
	}
	}