Support optional and named args in Function types.

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+# 8.6.2
+
+- Fix generation for fields that are `Function` types that are declared
+  separately, for example in a `mixin` defined in another source file, and use
+  named or positional parameters.
+
 # 8.6.1
 
 - Fix support for generating enum mixins for Dart 3. Instead of triggering

built_value_generator/lib/src/dart_types.dart

@@ -69,10 +69,31 @@ class DartTypes {
     } else if (dartType is DynamicType) {
       return 'dynamic';
     } else if (dartType is FunctionType) {
-      return getName(dartType.returnType) +
-          ' Function(' +
-          dartType.parameters.map((p) => getName(p.type)).join(', ') +
-          ')$suffix';
+      final parameters = StringBuffer();
+
+      parameters.write(
+          dartType.normalParameterTypes.map((t) => getName(t)).join(', '));
+
+      if (dartType.optionalParameterTypes.isNotEmpty) {
+        if (parameters.isNotEmpty) parameters.write(', ');
+        parameters.write('[');
+        parameters.write(
+            dartType.optionalParameterTypes.map((t) => getName(t)).join(', '));
+        parameters.write(']');
+      }
+
+      if (dartType.namedParameterTypes.isNotEmpty) {
+        if (parameters.isNotEmpty) parameters.write(', ');
+        parameters.write('{');
+        parameters.write(dartType.parameters
+            .where((p) => p.isOptionalNamed || p.isRequiredNamed)
+            .map((p) => '${p.isRequiredNamed ? 'required ' : ''}'
+                '${getName(p.type)} ${p.name}')
+            .join(', '));
+        parameters.write('}');
+      }
+
+      return getName(dartType.returnType) + ' Function($parameters)$suffix';
     } else if (dartType is InterfaceType) {
       var typeArguments = dartType.typeArguments;
       if (typeArguments.isEmpty) {

end_to_end_test/lib/mixins_src.dart

@@ -16,3 +16,13 @@ abstract class Mixin {
 
 // Don't fail on encountering new mixin syntax.
 mixin Foo {}
+
+mixin FunctionMixin {
+  Function get mixinBareFunction;
+  Future<void> Function(int, double) get mixinPositionalFunction;
+  Future<void> Function(int, [double]) get mixinOptionalFunction;
+  Future<void> Function(int x, double y) get mixinPositionalNamedFunction;
+  Future<void> Function(int x, {int y, double z}) get mixinNamedFunction;
+  Future<void> Function(int x, {required int y, required double z})
+      get mixinRequiredNamedFunction;
+}

end_to_end_test/lib/values.dart

@@ -1,12 +1,12 @@
 // Copyright (c) 2020, Google Inc. 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.
-// @dart=2.12
 
 import 'package:built_collection/built_collection.dart';
 import 'package:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';
 import 'package:end_to_end_test/enums.dart' as using_import_as;
+import 'package:end_to_end_test/mixins_src.dart';
 import 'package:fixnum/fixnum.dart';
 
 part 'values.g.dart';
@@ -931,3 +931,24 @@ abstract class ValueWithAwkwardNestedBuilderBuilder
       _$ValueWithAwkwardNestedBuilderBuilder;
   ValueWithAwkwardNestedBuilderBuilder._();
 }
+
+abstract class VariousFunctionsValue
+    // Functions declared in a different file are rendered via DartType instead
+    // of using the AST, so check those too.
+    with
+        FunctionMixin
+    implements
+        Built<VariousFunctionsValue, VariousFunctionsValueBuilder> {
+  Function get bareFunction;
+  Future<void> Function(int, double) get positionalFunction;
+  Future<void> Function(int, [double]) get optionalFunction;
+  Future<void> Function(int x, double y) get positionalNamedFunction;
+  Future<void> Function(int x, {int y, double z}) get namedFunction;
+  Future<void> Function(int x, {required int y, required double z})
+      get requiredNamedFunction;
+
+  factory VariousFunctionsValue(
+          [void Function(VariousFunctionsValueBuilder) updates]) =
+      _$VariousFunctionsValue;
+  VariousFunctionsValue._();
+}