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generic support #1552

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c426ff3
add support for generic conversions
Jan 25, 2026
6952a50
Merge branch 'google:master' into master
ManuelLeitner Jan 31, 2026
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22 changes: 15 additions & 7 deletions json_serializable/lib/src/type_helper_ctx.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@

import 'package:analyzer/dart/constant/value.dart';
import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/src/dart/constant/value.dart';
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@kevmoo kevmoo Jan 31, 2026

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This is NOT ideal...

import 'package:analyzer/dart/element/type.dart';
import 'package:source_helper/source_helper.dart';

Expand Down Expand Up @@ -122,12 +123,19 @@ ConvertData? _convertData(DartObject obj, FieldElement element, bool isFrom) {
if (objectValue == null || objectValue.isNull) {
return null;
}

final executableElement = objectValue.toFunctionValue()!;
var executableType = executableElement.type;
var qualifiedName = executableElement.qualifiedName;
final state = (objectValue as DartObjectImpl).state;
if (((state as FunctionState).typeArguments?.length ?? 0) > 0) {
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@gemini-code-assist gemini-code-assist bot Jan 31, 2026

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medium

This condition can be expressed more idiomatically using isNotEmpty.

Suggested change
if (((state as FunctionState).typeArguments?.length ?? 0) > 0) {
if ((state as FunctionState).typeArguments?.isNotEmpty == true) {

final generics = state.typeArguments!.cast<DartType>();
executableType = executableType.instantiate(generics);
qualifiedName += "<${generics.join(',')}>";
}
Comment on lines +129 to +134
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@gemini-code-assist gemini-code-assist bot Jan 31, 2026

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high

These changes rely on internal APIs from the analyzer package (DartObjectImpl, FunctionState), which are imported via package:analyzer/src/dart/constant/value.dart. These APIs are not stable and can break this package on any analyzer update, creating a significant maintenance risk.

Could you investigate if there's an alternative approach using only public APIs to retrieve the generic type arguments for the function? If this is the only way, the dependency on analyzer's internals should be clearly documented as a known risk.


if (executableElement.formalParameters.isEmpty ||
executableElement.formalParameters.first.isNamed ||
executableElement.formalParameters.where((pe) => !pe.isOptional).length >
if (executableType.formalParameters.isEmpty ||
executableType.formalParameters.first.isNamed ||
executableType.formalParameters.where((pe) => !pe.isOptional).length >
1) {
throwUnsupported(
element,
Expand All @@ -136,8 +144,8 @@ ConvertData? _convertData(DartObject obj, FieldElement element, bool isFrom) {
);
}

final returnType = executableElement.returnType;
final argType = executableElement.formalParameters.first.type;
final returnType = executableType.returnType;
final argType = executableType.formalParameters.first.type;
if (isFrom) {
final hasDefaultValue = !jsonKeyAnnotation(
element,
Expand Down Expand Up @@ -179,5 +187,5 @@ ConvertData? _convertData(DartObject obj, FieldElement element, bool isFrom) {
}
}

return ConvertData(executableElement.qualifiedName, argType, returnType);
return ConvertData(qualifiedName, argType, returnType);
}
18 changes: 15 additions & 3 deletions json_serializable/lib/src/type_helpers/json_converter_helper.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@

import 'package:analyzer/dart/constant/value.dart';
import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/dart/element/nullability_suffix.dart';
import 'package:analyzer/dart/element/type.dart';
import 'package:json_annotation/json_annotation.dart';
import 'package:source_gen/source_gen.dart';
Expand Down Expand Up @@ -281,9 +282,20 @@ _ConverterMatch? _compatibleMatch(
ElementAnnotation? annotation,
DartObject constantValue,
) {
final converterClassElement = constantValue.type!.element as ClassElement;
var converterClassType = constantValue.type! as InterfaceType;
final converterClassElement = converterClassType.element as ClassElement;
String? genericTypeArg;

final generics = (constantValue.type as InterfaceType).typeArguments;
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medium

The converterClassType variable is already assigned constantValue.type as InterfaceType on line 285. You can reuse it here to avoid the redundant cast and access.

Suggested change
final generics = (constantValue.type as InterfaceType).typeArguments;
final generics = converterClassType.typeArguments;

if (generics.isNotEmpty) {
converterClassType = converterClassElement.instantiate(
typeArguments: generics,
nullabilitySuffix: NullabilitySuffix.none,
);
genericTypeArg = generics.join(", ");
}

final jsonConverterSuper = converterClassElement.allSupertypes
final jsonConverterSuper = converterClassType.allSupertypes
.where((e) => _jsonConverterChecker.isExactly(e.element))
.singleOrNull;

Expand All @@ -302,7 +314,7 @@ _ConverterMatch? _compatibleMatch(
annotation,
constantValue,
jsonConverterSuper.typeArguments[1],
null,
genericTypeArg,
fieldType,
);
}
Expand Down
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