Finish implementation of defaultValue (#191)

Implementation for `checked` option
Improve error messages on unsupported types
Explicitly disallow defaultValue + non-nullable field
support serialization of single enum values

Fixes #74

Also added $enumDecode[Nullable] helpers to json_annotation

Author: kevmoo

json_annotation/CHANGELOG.md

@@ -2,14 +2,18 @@
 
 * Added `JsonKey.defaultValue`.
 
+* Added helpers for deserialization of `enum` values.
+  These functions starting with `$` are  referenced by generated code.
+  They are not meant for direct use.
+
 ## 0.2.5
 
 * Added `CheckedFromJsonException` which is thrown by code generated when
  `checked` is enabled in `json_serializable`.
 
-* Added functions to support the `checked` generation option. These
-  functions start with `$` are referenced by generated code. They are not meant
-  for direct use.
+* Added functions to support the `checked` generation option.
+  These functions starting with `$` are referenced by generated code.
+  They are not meant for direct use.
 
 ## 0.2.4
 

json_annotation/lib/src/json_serializable.dart

@@ -133,3 +133,45 @@ class JsonKey {
       this.toJson,
       this.defaultValue});
 }
+
+// Until enum supports parse: github.com/dart-lang/sdk/issues/33244
+/// *Helper function used in generated code with `enum` values – should not be
+/// used directly.*
+///
+/// Returns an enum instance corresponding to [enumValue] from the enum named
+/// [enumName] with [values].
+///
+/// If [enumValue] is null or no corresponding values exists, an `ArgumentError`
+/// is thrown.
+///
+/// Given an enum named `Example`, an invocation would look like
+///
+/// ```dart
+/// $enumDecode('Example', Example.values, 'desiredValue')
+/// ```
+T $enumDecode<T>(String enumName, List<T> values, String enumValue) =>
+    values.singleWhere((e) => e.toString() == '$enumName.$enumValue',
+        orElse: () => throw new ArgumentError(
+            '`$enumValue` is not one of the supported values: '
+            '${values.map(_nameForEnumValue).join(', ')}'));
+
+/// *Helper function used in generated code with `enum` values – should not be
+/// used directly.*
+///
+/// Returns an enum instance corresponding to [enumValue] from the enum named
+/// [enumName] with [values].
+///
+/// If [enumValue] is `null`, `null` is returned.
+///
+/// If no corresponding values exists, an `ArgumentError` is thrown.
+///
+/// Given an enum named `Example`, an invocation would look like
+///
+/// ```dart
+/// $enumDecodeNullable('Example', Example.values, 'desiredValue')
+/// ```
+T $enumDecodeNullable<T>(String enumName, List<T> values, String enumValue) =>
+    enumValue == null ? null : $enumDecode(enumName, values, enumValue);
+
+// Until enum has a name property: github.com/dart-lang/sdk/issues/21712
+String _nameForEnumValue(Object value) => value.toString().split('.')[1];

json_serializable/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 * Added support for `JsonKey.defaultValue`.
 
+* `enum` deserialization now uses helpers provided by `json_annotation`.
+
 * Small change to how nullable `Map` values are deserialized.
 
 * Small whitespace changes to `JsonLiteral` generation to align with `dartfmt`.

json_serializable/lib/src/generator_helper.dart

@@ -382,34 +382,37 @@ class ${_wrapperClassName(true)} extends \$JsonMapWrapper {
   String _deserializeForField(FieldElement field,
       {ParameterElement ctorParam, bool checkedProperty}) {
     checkedProperty ??= false;
-    var defaultValue = jsonKeyFor(field).defaultValue;
     var jsonKeyName = _safeNameAccess(field);
-
     var targetType = ctorParam?.type ?? field.type;
+    var contextHelper = _getHelperContext(field);
 
+    String value;
     try {
       if (_generator.checked) {
-        // TODO: default value fun here!
-        var value = _getHelperContext(field).deserialize(targetType, 'v');
-        if (checkedProperty) {
-          return value;
+        value = contextHelper.deserialize(targetType, 'v');
+        if (!checkedProperty) {
+          value = '\$checkedConvert(json, $jsonKeyName, (v) => $value)';
         }
+      } else {
+        assert(!checkedProperty,
+            'should only be true if `_generator.checked` is true.');
 
-        return '\$checkedConvert(json, $jsonKeyName, (v) => $value)';
-      }
-      assert(!checkedProperty,
-          'should only be true if `_generator.checked` is true.');
-
-      var value = _getHelperContext(field)
-          .deserialize(targetType, 'json[$jsonKeyName]');
-
-      if (defaultValue != null) {
-        value = '$value ?? $defaultValue';
+        value = contextHelper.deserialize(targetType, 'json[$jsonKeyName]');
       }
-      return value;
     } on UnsupportedTypeError catch (e) {
       throw _createInvalidGenerationError('fromJson', field, e);
     }
+
+    var defaultValue = jsonKeyFor(field).defaultValue;
+    if (defaultValue != null) {
+      if (!contextHelper.nullable) {
+        throwUnsupported(field,
+            'Cannot use `defaultValue` on a field with `nullable` false.');
+      }
+
+      value = '$value ?? $defaultValue';
+    }
+    return value;
   }
 
   TypeHelperContext _getHelperContext(FieldElement field) {

json_serializable/lib/src/json_key_helpers.dart

@@ -11,9 +11,10 @@ import 'package:meta/meta.dart' show alwaysThrows;
 import 'package:source_gen/source_gen.dart';
 
 import 'json_literal_generator.dart';
+import 'utils.dart';
 
 @alwaysThrows
-T _throwUnsupported<T>(FieldElement element, String message) =>
+void throwUnsupported(FieldElement element, String message) =>
     throw new InvalidGenerationSourceError(
         'Error with `@JsonKey` on `${element.name}`. $message',
         element: element);
@@ -45,41 +46,71 @@ JsonKeyWithConversion _from(FieldElement element) {
   var fromJsonName = _getFunctionName(obj, element, true);
   var toJsonName = _getFunctionName(obj, element, false);
 
-  Object _getLiteral(DartObject dartObject) {
+  Object _getLiteral(DartObject dartObject, Iterable<String> things) {
     if (dartObject.isNull) {
       return null;
     }
 
     var reader = new ConstantReader(dartObject);
 
+    String badType;
     if (reader.isSymbol) {
-      _throwUnsupported(element,
-          'Values of type `Symbol` are not supported for `defaultValue`.');
+      badType = 'Symbol';
     } else if (reader.isType) {
-      _throwUnsupported(element,
-          'Values of type `Type` are not supported for `defaultValue`.');
+      badType = 'Type';
+    } else if (dartObject.type is FunctionType) {
+      // TODO(kevmoo): Support calling function for the default value?
+      badType = 'Function';
     } else if (!reader.isLiteral) {
-      _throwUnsupported(
-          element, 'The provided `defaultValue` is not a literal: $dartObject');
+      badType = dartObject.type.name;
+    }
+
+    if (badType != null) {
+      badType = things.followedBy([badType]).join(' > ');
+      throwUnsupported(
+          element, '`defaultValue` is `$badType`, it must be a literal.');
     }
 
     var literal = reader.literalValue;
+
     if (literal is num || literal is String || literal is bool) {
       return literal;
     } else if (literal is List<DartObject>) {
-      return literal.map(_getLiteral).toList();
-    } else if (literal is Map<DartObject, DartObject>) {
       return literal
-          .map((k, v) => new MapEntry(_getLiteral(k), _getLiteral(v)));
+          .map((e) => _getLiteral(e, things.followedBy(['List'])))
+          .toList();
+    } else if (literal is Map<DartObject, DartObject>) {
+      var mapThings = things.followedBy(['Map']);
+      return literal.map((k, v) =>
+          new MapEntry(_getLiteral(k, mapThings), _getLiteral(v, mapThings)));
     }
-    _throwUnsupported(
-        element, 'The provided value is not supported: $dartObject');
-  }
 
-  var defaultValueLiteral = _getLiteral(obj.getField('defaultValue'));
+    badType = things.followedBy(['$dartObject']).join(' > ');
 
-  if (defaultValueLiteral != null) {
-    defaultValueLiteral = jsonLiteralAsDart(defaultValueLiteral, false);
+    throwUnsupported(
+        element,
+        'The provided value is not supported: $badType. '
+        'This may be an error in package:json_serializable. '
+        'Please rerun your build with `--verbose` and file an issue.');
+  }
+
+  var defaultValueObject = obj.getField('defaultValue');
+
+  Object defaultValueLiteral;
+  if (isEnum(defaultValueObject.type)) {
+    var interfaceType = defaultValueObject.type as InterfaceType;
+    var allowedValues = interfaceType.accessors
+        .where((p) => p.returnType == interfaceType)
+        .map((p) => p.name)
+        .toList();
+    var enumValueIndex = defaultValueObject.getField('index').toIntValue();
+    defaultValueLiteral =
+        '${interfaceType.name}.${allowedValues[enumValueIndex]}';
+  } else {
+    defaultValueLiteral = _getLiteral(defaultValueObject, []);
+    if (defaultValueLiteral != null) {
+      defaultValueLiteral = jsonLiteralAsDart(defaultValueLiteral, false);
+    }
   }
 
   return new JsonKeyWithConversion._(
@@ -130,7 +161,7 @@ ConvertData _getFunctionName(
   var type = objectValue.type as FunctionType;
 
   if (type.element is MethodElement) {
-    _throwUnsupported(
+    throwUnsupported(
         element,
         'The function provided for `$paramName` must be top-level. '
         'Static class methods (`${type.element.name}`) are not supported.');
@@ -140,7 +171,7 @@ ConvertData _getFunctionName(
   if (functionElement.parameters.isEmpty ||
       functionElement.parameters.first.isNamed ||
       functionElement.parameters.where((pe) => !pe.isOptional).length > 1) {
-    _throwUnsupported(
+    throwUnsupported(
         element,
         'The `$paramName` function `${functionElement.name}` must have one '
         'positional paramater.');
@@ -155,7 +186,7 @@ ConvertData _getFunctionName(
       // to the `fromJson` function.
       // TODO: consider adding error checking here if there is confusion.
     } else if (!returnType.isAssignableTo(element.type)) {
-      _throwUnsupported(
+      throwUnsupported(
           element,
           'The `$paramName` function `${functionElement.name}` return type '
           '`$returnType` is not compatible with field type `${element.type}`.');
@@ -166,7 +197,7 @@ ConvertData _getFunctionName(
       // to the `fromJson` function.
       // TODO: consider adding error checking here if there is confusion.
     } else if (!element.type.isAssignableTo(argType)) {
-      _throwUnsupported(
+      throwUnsupported(
           element,
           'The `$paramName` function `${functionElement.name}` argument type '
           '`$argType` is not compatible with field type'

json_serializable/lib/src/type_helpers/enum_helper.dart

@@ -4,7 +4,6 @@
 
 import 'package:analyzer/dart/element/type.dart';
 
-import '../constants.dart' as consts;
 import '../type_helper.dart';
 import '../utils.dart';
 
@@ -31,18 +30,9 @@ class EnumHelper extends TypeHelper {
       return null;
     }
 
-    var wrappedExpression =
-        simpleExpression.hasMatch(expression) ? expression : '{$expression}';
-
-    var closureArg = consts.closureArg;
-    if (closureArg == wrappedExpression) {
-      closureArg = '${closureArg}2';
-    }
-
-    return commonNullPrefix(
-        context.nullable,
-        expression,
-        '$targetType.values.singleWhere(($closureArg) => $closureArg.toString()'
-        " == '$targetType.\$$wrappedExpression')");
+    var functionName =
+        context.nullable ? r'$enumDecodeNullable' : r'$enumDecode';
+    return "$functionName('$targetType', $targetType.values, "
+        '$expression as String)';
   }
 }

json_serializable/test/default_value/default_value.non_nullable.dart renamed to json_serializable/test/default_value/default_value.checked.dart

@@ -5,19 +5,27 @@
 // GENERATED CODE - DO NOT MODIFY BY HAND
 
 // **************************************************************************
-// Generator: _NonNullableGenerator
+// Generator: _CheckedGenerator
 // **************************************************************************
 
 // ignore_for_file: annotate_overrides
 
 import 'package:json_annotation/json_annotation.dart';
 
-part 'default_value.non_nullable.g.dart';
+import 'default_value_interface.dart' as dvi hide Greek;
+import 'default_value_interface.dart' show Greek;
+
+part 'default_value.checked.g.dart';
 
 const _intValue = 42;
 
-@JsonSerializable(nullable: false)
-class DefaultValue extends Object with _$DefaultValueSerializerMixin {
+dvi.DefaultValue fromJson(Map<String, dynamic> json) =>
+    _$DefaultValueFromJson(json);
+
+@JsonSerializable()
+class DefaultValue extends Object
+    with _$DefaultValueSerializerMixin
+    implements dvi.DefaultValue {
   @JsonKey(defaultValue: true)
   bool fieldBool;
 
@@ -47,6 +55,9 @@ class DefaultValue extends Object with _$DefaultValueSerializerMixin {
   })
   Map<String, List<String>> fieldMapListString;
 
+  @JsonKey(defaultValue: Greek.beta)
+  Greek fieldEnum;
+
   DefaultValue();
 
   factory DefaultValue.fromJson(Map<String, dynamic> json) =>