Fix nnbd generation around type converters (#968)

moor/test/data/tables/custom_tables.g.dart

@@ -289,8 +289,8 @@ class ConfigTable extends Table with TableInfo<ConfigTable, Config> {
     return ConfigTable(_db, alias);
   }
 
-  static TypeConverter<SyncType?, int?> $converter0 = const SyncTypeConverter();
-  static TypeConverter<SyncType?, int?> $converter1 =
+  static TypeConverter<SyncType, int> $converter0 = const SyncTypeConverter();
+  static TypeConverter<SyncType?, int> $converter1 =
       const EnumIndexConverter<SyncType>(SyncType.values);
   @override
   bool get dontWriteConstraints => true;
@@ -1614,7 +1614,7 @@ abstract class _$CustomTablesDb extends GeneratedDatabase {
         readsFrom: {config}).map(config.mapFromRow);
   }
 
-  Selectable<String> typeConverterVar(SyncType? var1, List<SyncType?> var2) {
+  Selectable<String> typeConverterVar(SyncType var1, List<SyncType?> var2) {
     var $arrayStartIndex = 2;
     final expandedvar2 = $expandVar($arrayStartIndex, var2.length);
     $arrayStartIndex += var2.length;
@@ -1623,7 +1623,7 @@ abstract class _$CustomTablesDb extends GeneratedDatabase {
         variables: [
           Variable<int>(ConfigTable.$converter0.mapToSql(var1)!),
           for (var $ in var2)
-            Variable<int>(ConfigTable.$converter1.mapToSql($)!)
+            Variable<int?>(ConfigTable.$converter1.mapToSql($)!)
         ],
         readsFrom: {
           config

moor/test/data/tables/todos.g.dart

@@ -558,7 +558,7 @@ class $CategoriesTable extends Categories
     return $CategoriesTable(_db, alias);
   }
 
-  static TypeConverter<CategoryPriority, int?> $converter0 =
+  static TypeConverter<CategoryPriority, int> $converter0 =
       const EnumIndexConverter<CategoryPriority>(CategoryPriority.values);
 }
 
@@ -1316,7 +1316,7 @@ class $TableWithoutPKTable extends TableWithoutPK
     return $TableWithoutPKTable(_db, alias);
   }
 
-  static TypeConverter<MyCustomObject, String?> $converter0 =
+  static TypeConverter<MyCustomObject, String> $converter0 =
       const CustomConverter();
 }
 

moor_generator/lib/src/analyzer/moor/create_table_reader.dart

@@ -11,6 +11,7 @@ import 'package:moor_generator/src/model/used_type_converter.dart';
 import 'package:moor_generator/src/utils/names.dart';
 import 'package:moor_generator/src/utils/string_escaper.dart';
 import 'package:moor_generator/src/utils/type_converter_hint.dart';
+import 'package:moor_generator/src/utils/type_utils.dart';
 import 'package:recase/recase.dart';
 import 'package:sqlparser/sqlparser.dart';
 
@@ -217,8 +218,11 @@ class CreateTableReader {
     }
 
     final interfaceType = type as InterfaceType;
-    // TypeConverter declares a "D mapToDart(S fromDb);". We need to know D
-    final typeInDart = interfaceType.getMethod('mapToDart').returnType;
+    final asTypeConverter = interfaceType.allSupertypes.firstWhere(
+        (type) => isFromMoor(type) && type.element.name == 'TypeConverter');
+
+    // TypeConverter<D, S>, where D is the type in Dart
+    final typeInDart = asTypeConverter.typeArguments.first;
 
     return UsedTypeConverter(
         expression: code, mappedType: typeInDart, sqlType: sqlType);

moor_generator/lib/src/model/types.dart

@@ -17,6 +17,11 @@ abstract class HasType {
 }
 
 extension OperationOnTypes on HasType {
+  /// Whether this type is nullable in Dart
+  bool get nullableInDart {
+    return nullable || typeConverter?.hasNullableDartType == true;
+  }
+
   /// the Dart type of this column that can be handled by moors type mapping.
   /// Basically the same as [dartTypeCode], minus custom types and nullability.
   String get variableTypeName => dartTypeNames[type];
@@ -30,7 +35,7 @@ extension OperationOnTypes on HasType {
   /// This is the same as [dartTypeCode] but without custom types.
   String variableTypeCode(
       [GenerationOptions options = const GenerationOptions()]) {
-    final hasSuffix = nullable && options.nnbd;
+    final hasSuffix = nullableInDart && options.nnbd;
     return hasSuffix ? '$variableTypeName?' : variableTypeName;
   }
 
@@ -39,7 +44,10 @@ extension OperationOnTypes on HasType {
   /// [int].
   String dartTypeCode([GenerationOptions options = const GenerationOptions()]) {
     if (typeConverter != null) {
-      return typeConverter.mappedType?.codeString(options);
+      final needsSuffix = nullable && !typeConverter.hasNullableDartType;
+      final baseType = typeConverter.mappedType.codeString(options);
+
+      return needsSuffix ? '$baseType?' : baseType;
     }
 
     return variableTypeCode(options);

moor_generator/lib/src/model/used_type_converter.dart

@@ -37,6 +37,9 @@ class UsedTypeConverter {
     @required this.sqlType,
   });
 
+  bool get hasNullableDartType =>
+      mappedType.nullabilitySuffix == NullabilitySuffix.question;
+
   factory UsedTypeConverter.forEnumColumn(DartType enumType, bool nullable) {
     if (enumType.element is! ClassElement) {
       throw InvalidTypeForEnumConverterException('Not a class', enumType);
@@ -61,7 +64,7 @@ class UsedTypeConverter {
 
   /// A suitable typename to store an instance of the type converter used here.
   String converterNameInCode(GenerationOptions options) {
-    final sqlDartType = options.nullableType(dartTypeNames[sqlType]);
+    final sqlDartType = dartTypeNames[sqlType];
     return 'TypeConverter<${mappedType.codeString(options)}, $sqlDartType>';
   }
 }

moor_generator/lib/src/writer/tables/data_class_writer.dart

@@ -176,15 +176,17 @@ class DataClassWriter {
     for (var i = 0; i < table.columns.length; i++) {
       final column = table.columns[i];
       final last = i == table.columns.length - 1;
+      final isNullable = column.nullableInDart;
 
       final typeName = column.dartTypeCode(scope.generationOptions);
-      if (wrapNullableInValue && column.nullable) {
+      if (wrapNullableInValue && isNullable) {
         _buffer
           ..write('Value<$typeName> ${column.dartGetterName} ')
           ..write('= const Value.absent()');
-      } else if (!column.nullable && scope.generationOptions.nnbd) {
-        // We always write nullable types in the copyWith constructor, since all
-        // parameters are optional.
+      } else if (!isNullable && scope.generationOptions.nnbd) {
+        // We always use nullable parameters in copyWith, since all parameters
+        // are optional. The !isNullable check is there to avoid a duplicate
+        // question mark in the type name.
         _buffer.write('$typeName? ${column.dartGetterName}');
       } else {
         _buffer.write('$typeName ${column.dartGetterName}');