[ffigen] Dedupe ObjC listener block trampolines (#1541)

pkgs/ffigen/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 14.1.0-wip
+
+- Dedupe `ObjCBlock` trampolines to reduce generated ObjC code.
+
 ## 14.0.1
 
 - Fix bug with nullable types in `ObjCBlock`'s type arguments:

pkgs/ffigen/lib/src/code_generator/library.dart

@@ -20,6 +20,8 @@ class Library {
   /// List of bindings in this library.
   late List<Binding> bindings;
 
+  final ObjCBuiltInFunctions? objCBuiltInFunctions;
+
   late Writer _writer;
   Writer get writer => _writer;
 
@@ -34,6 +36,7 @@ class Library {
     List<LibraryImport>? libraryImports,
     bool silenceEnumWarning = false,
     List<String> nativeEntryPoints = const <String>[],
+    this.objCBuiltInFunctions,
   }) {
     _findBindings(bindings, sort);
 
@@ -103,6 +106,7 @@ class Library {
     for (final b in original) {
       b.addDependencies(dependencies);
     }
+    objCBuiltInFunctions?.addDependencies(dependencies);
 
     /// Save bindings.
     bindings = dependencies.toList();

pkgs/ffigen/lib/src/code_generator/objc_block.dart

@@ -3,22 +3,23 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import '../code_generator.dart';
-import '../config_provider/config_types.dart';
 import '../header_parser/data.dart' show bindingsIndex;
 
 import 'binding_string.dart';
 import 'writer.dart';
 
 class ObjCBlock extends BindingType {
+  final ObjCBuiltInFunctions builtInFunctions;
   final Type returnType;
   final List<Parameter> params;
   final bool returnsRetained;
-  Func? _wrapListenerBlock;
+  ObjCListenerBlockTrampoline? _wrapListenerBlock;
 
   factory ObjCBlock({
     required Type returnType,
     required List<Parameter> params,
     required bool returnsRetained,
+    required ObjCBuiltInFunctions builtInFunctions,
   }) {
     final usr = _getBlockUsr(returnType, params, returnsRetained);
 
@@ -33,6 +34,7 @@ class ObjCBlock extends BindingType {
       returnType: returnType,
       params: params,
       returnsRetained: returnsRetained,
+      builtInFunctions: builtInFunctions,
     );
     bindingsIndex.addObjCBlockToSeen(usr, block);
 
@@ -45,6 +47,7 @@ class ObjCBlock extends BindingType {
     required this.returnType,
     required this.params,
     required this.returnsRetained,
+    required this.builtInFunctions,
   }) : super(originalName: name);
 
   // Generates a human readable name for the block based on the args and return
@@ -213,7 +216,7 @@ abstract final class $name {
       );
       final listenerConvFn =
           '($paramsFfiDartType) => $listenerConvFnInvocation';
-      final wrapFn = _wrapListenerBlock?.name;
+      final wrapFn = _wrapListenerBlock?.func.name;
       final releaseFn = ObjCBuiltInFunctions.objectRelease.gen(w);
 
       s.write('''
@@ -278,7 +281,8 @@ ref.pointer.ref.invoke.cast<$natTrampFnType>().asFunction<$trampFuncFfiDartType>
 
   @override
   BindingString? toObjCBindingString(Writer w) {
-    if (_wrapListenerBlock == null) return null;
+    if (_wrapListenerBlock?.objCBindingsGenerated ?? true) return null;
+    _wrapListenerBlock!.objCBindingsGenerated = true;
 
     final argsReceived = <String>[];
     final retains = <String>[];
@@ -288,15 +292,17 @@ ref.pointer.ref.invoke.cast<$natTrampFnType>().asFunction<$trampFuncFfiDartType>
       argsReceived.add(param.getNativeType(varName: argName));
       retains.add(param.type.generateRetain(argName) ?? argName);
     }
-    final fnName = _wrapListenerBlock!.name;
-    final blockTypedef = w.objCLevelUniqueNamer.makeUnique('ListenerBlock');
+    final argStr = argsReceived.join(', ');
+    final fnName = _wrapListenerBlock!.func.name;
+    final blockName = w.objCLevelUniqueNamer.makeUnique('_ListenerTrampoline');
+    final blockTypedef = '${returnType.getNativeType()} (^$blockName)($argStr)';
 
     final s = StringBuffer();
     s.write('''
 
-typedef ${getNativeType(varName: blockTypedef)};
-$blockTypedef $fnName($blockTypedef block) NS_RETURNS_RETAINED {
-  return ^void(${argsReceived.join(', ')}) {
+typedef $blockTypedef;
+$blockName $fnName($blockName block) NS_RETURNS_RETAINED {
+  return ^void($argStr) {
     block(${retains.join(', ')});
   };
 }
@@ -315,17 +321,8 @@ $blockTypedef $fnName($blockTypedef block) NS_RETURNS_RETAINED {
       p.type.addDependencies(dependencies);
     }
 
-    if (hasListener && params.any((p) => p.type.generateRetain('') != null)) {
-      _wrapListenerBlock = Func(
-        name: 'wrapListenerBlock_$name',
-        returnType: this,
-        parameters: [Parameter(name: 'block', type: this, objCConsumed: false)],
-        objCReturnsRetained: true,
-        isLeaf: true,
-        isInternal: true,
-        useNameForLookup: true,
-        ffiNativeConfig: const FfiNativeConfig(enabled: true),
-      )..addDependencies(dependencies);
+    if (hasListener) {
+      _wrapListenerBlock = builtInFunctions.getListenerBlockTrampoline(this);
     }
   }
 
@@ -342,10 +339,7 @@ $blockTypedef $fnName($blockTypedef block) NS_RETURNS_RETAINED {
   String getObjCBlockSignatureType(Writer w) => getDartType(w);
 
   @override
-  String getNativeType({String varName = ''}) {
-    final paramStrs = params.map<String>((p) => p.getNativeType());
-    return '${returnType.getNativeType()} (^$varName)(${paramStrs.join(', ')})';
-  }
+  String getNativeType({String varName = ''}) => 'id $varName';
 
   @override
   bool get sameFfiDartAndCType => true;

pkgs/ffigen/lib/src/code_generator/objc_built_in_functions.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import '../code_generator.dart';
+import '../config_provider/config_types.dart';
 
 import 'binding_string.dart';
 import 'writer.dart';
@@ -12,6 +13,7 @@ class ObjCBuiltInFunctions {
   ObjCBuiltInFunctions(this.generateForPackageObjectiveC);
 
   final bool generateForPackageObjectiveC;
+  var _depsAdded = false;
 
   static const registerName = ObjCImport('registerName');
   static const getClass = ObjCImport('getClass');
@@ -116,6 +118,7 @@ class ObjCBuiltInFunctions {
   // for float return types we need objc_msgSend_fpret.
   final _msgSendFuncs = <String, ObjCMsgSendFunc>{};
   ObjCMsgSendFunc getMsgSendFunc(Type returnType, List<Parameter> params) {
+    assert(!_depsAdded);
     var key = returnType.cacheKey();
     for (final p in params) {
       key += ' ${p.type.cacheKey()}';
@@ -129,19 +132,63 @@ class ObjCBuiltInFunctions {
 
   final _selObjects = <String, ObjCInternalGlobal>{};
   ObjCInternalGlobal getSelObject(String methodName) {
+    assert(!_depsAdded);
     return _selObjects[methodName] ??= ObjCInternalGlobal(
       '_sel_${methodName.replaceAll(":", "_")}',
       (Writer w) => '${registerName.gen(w)}("$methodName")',
     );
   }
 
+  final _blockTrampolines = <String, ObjCListenerBlockTrampoline>{};
+  ObjCListenerBlockTrampoline? getListenerBlockTrampoline(ObjCBlock block) {
+    assert(!_depsAdded);
+
+    var needsTrampoline = false;
+    final paramIds = <String>[];
+    for (final param in block.params) {
+      final retainFunc = param.type.generateRetain('');
+      if (retainFunc != null) {
+        needsTrampoline = true;
+      }
+
+      // The trampoline ID is based on the getNativeType of the param. Objects
+      // and blocks both have `id` as their native type, but need separate
+      // trampolines since they have different retain functions. So add the
+      // retainFunc (if any) to all the param IDs.
+      paramIds.add('${param.getNativeType()}-${retainFunc ?? ''}');
+    }
+    if (!needsTrampoline) return null;
+    final id = paramIds.join(',');
+
+    return _blockTrampolines[id] ??= ObjCListenerBlockTrampoline(Func(
+      name: '_wrapListenerBlock_${id.hashCode.toRadixString(16)}',
+      returnType: PointerType(objCBlockType),
+      parameters: [
+        Parameter(
+            name: 'block',
+            type: PointerType(objCBlockType),
+            objCConsumed: false)
+      ],
+      objCReturnsRetained: true,
+      isLeaf: true,
+      isInternal: true,
+      useNameForLookup: true,
+      ffiNativeConfig: const FfiNativeConfig(enabled: true),
+    ));
+  }
+
   void addDependencies(Set<Binding> dependencies) {
+    if (_depsAdded) return;
+    _depsAdded = true;
     for (final msgSendFunc in _msgSendFuncs.values) {
       msgSendFunc.addDependencies(dependencies);
     }
     for (final sel in _selObjects.values) {
       sel.addDependencies(dependencies);
     }
+    for (final tramp in _blockTrampolines.values) {
+      tramp.func.addDependencies(dependencies);
+    }
   }
 
   static bool isInstanceType(Type type) {
@@ -151,6 +198,13 @@ class ObjCBuiltInFunctions {
   }
 }
 
+/// A native trampoline function for a listener block.
+class ObjCListenerBlockTrampoline {
+  final Func func;
+  bool objCBindingsGenerated = false;
+  ObjCListenerBlockTrampoline(this.func);
+}
+
 /// A function, global variable, or helper type defined in package:objective_c.
 class ObjCImport {
   final String name;

pkgs/ffigen/lib/src/code_generator/objc_interface.dart

@@ -256,8 +256,6 @@ class ObjCInterface extends BindingType with ObjCMethods {
       // Add dependencies for any methods that were added.
       addMethodDependencies(dependencies, needMsgSend: true);
     }
-
-    builtInFunctions.addDependencies(dependencies);
   }
 
   void _copyMethodsFromSuperType() {
@@ -318,7 +316,7 @@ class ObjCInterface extends BindingType with ObjCMethods {
       _isBuiltIn ? '${w.objcPkgPrefix}.$name' : name;
 
   @override
-  String getNativeType({String varName = ''}) => '$originalName* $varName';
+  String getNativeType({String varName = ''}) => 'id $varName';
 
   @override
   String getObjCBlockSignatureType(Writer w) => getDartType(w);

pkgs/ffigen/lib/src/code_generator/objc_methods.dart

@@ -225,6 +225,7 @@ class ObjCMethod {
           ...params,
         ],
         returnsRetained: returnsRetained,
+        builtInFunctions: builtInFunctions,
       )..addDependencies(dependencies);
     }
   }

pkgs/ffigen/lib/src/header_parser/parser.dart

@@ -35,6 +35,7 @@ Library parse(Config c) {
     libraryImports: c.libraryImports.values.toList(),
     silenceEnumWarning: c.silenceEnumWarning,
     nativeEntryPoints: c.entryPoints.map((uri) => uri.toFilePath()).toList(),
+    objCBuiltInFunctions: objCBuiltInFunctions,
   );
 
   return library;

pkgs/ffigen/lib/src/header_parser/sub_parsers/objc_block_parser.dart

@@ -27,5 +27,6 @@ ObjCBlock parseObjCBlock(clang_types.CXType cxtype) {
     returnType: returnType,
     params: params,
     returnsRetained: false,
+    builtInFunctions: objCBuiltInFunctions,
   );
 }

pkgs/ffigen/pubspec.yaml

@@ -3,7 +3,7 @@
 # BSD-style license that can be found in the LICENSE file.
 
 name: ffigen
-version: 14.0.1
+version: 14.1.0-wip
 description: >
   Generator for FFI bindings, using LibClang to parse C, Objective-C, and Swift
   files.

pkgs/ffigen/test/native_objc_test/block_test.dart

@@ -667,6 +667,23 @@ void main() {
       expect(descPtr.ref.dispose_helper, isNot(nullptr));
       expect(descPtr.ref.signature, nullptr);
     });
+
+    test('Block trampoline args converted to id', () {
+      final objCBindings =
+          File('test/native_objc_test/block_bindings.m').readAsStringSync();
+
+      // Objects are converted to id.
+      expect(objCBindings, isNot(contains('NSObject')));
+      expect(objCBindings, isNot(contains('NSString')));
+      expect(objCBindings, contains('id'));
+
+      // Blocks are also converted to id. Note: (^) is part of a block type.
+      expect(objCBindings, isNot(contains('(^)')));
+
+      // Other types, like structs, are still there.
+      expect(objCBindings, contains('Vec2'));
+      expect(objCBindings, contains('Vec4'));
+    });
   });
 }