Qualifier error. No method found annotated with @Named#value: [ quantityConverter ].
See https://mapstruct.org/faq/#qualifier for more info.

Can't map "1" to "String quantity".

import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.Named;
import org.mapstruct.factory.Mappers;

/**
 * MapStruct Issue Demo: defaultValue with qualifiedByName compilation error
 *
 * Issue Description:
 * When using @Mapping with source, qualifiedByName, and defaultValue together,
 * MapStruct 1.6.2 fails to compile with error:
 * "Qualifier error. No method found annotated with @Named#value: [ quantityConverter ]"
 * "Can't map "1" to "String quantity"
 *
 * This works fine in MapStruct 1.1.0.Final but fails in 1.6.2
 */
public class MapStructIssueDemo {

    // Source object
    public static class SourceObject {
        private String name;
        private DataWrapper dataWrapper;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public DataWrapper getDataWrapper() {
            return dataWrapper;
        }

        public void setDataWrapper(DataWrapper dataWrapper) {
            this.dataWrapper = dataWrapper;
        }
    }

    // Data wrapper
    public static class DataWrapper {
        private Integer count;

        public Integer getCount() {https://docs.github.com/github/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax
            return count;
        }

        public void setCount(Integer count) {
            this.count = count;
        }
    }

    // Target object
    public static class TargetObject {
        private String name;
        private String quantity;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getQuantity() {
            return quantity;
        }

        public void setQuantity(String quantity) {
            this.quantity = quantity;
        }
    }

    // Converter class with @Named method
    public static class DataConverter {

        @Named("quantityConverter")
        public String quantityConverter(DataWrapper dataWrapper) {
            if (dataWrapper == null || dataWrapper.getCount() == null) {
                return null;
            }
            return String.valueOf(dataWrapper.getCount());
        }
    }

    // Mapper interface - THIS WILL FAIL TO COMPILE with MapStruct 1.6.2
    @Mapper(uses = {DataConverter.class})
    public interface IssueMapper {

        IssueMapper INSTANCE = Mappers.getMapper(IssueMapper.class);

        // This mapping causes compilation error in MapStruct 1.6.2
        // Error: Qualifier error. No method found annotated with @Named#value: [ quantityConverter ]
        // Error: Can't map "1" to "String quantity"
        @Mapping(target = "name", source = "name")
        @Mapping(target = "quantity", source = "dataWrapper", qualifiedByName = "quantityConverter", defaultValue = "1")
        TargetObject convert(SourceObject source);
    }

    // Workaround 1: Remove defaultValue (THIS WORKS)
    @Mapper(uses = {DataConverter.class})
    public interface WorkaroundMapper1 {

        WorkaroundMapper1 INSTANCE = Mappers.getMapper(WorkaroundMapper1.class);

        @Mapping(target = "name", source = "name")
        @Mapping(target = "quantity", source = "dataWrapper", qualifiedByName = "quantityConverter")
        TargetObject convert(SourceObject source);
    }

    // Workaround 2: Handle default value in converter method
    public static class DataConverterWithDefault {

        @Named("quantityConverterWithDefault")
        public String quantityConverterWithDefault(DataWrapper dataWrapper) {
            if (dataWrapper == null || dataWrapper.getCount() == null) {
                return "1"; // Return default value in converter
            }
            return String.valueOf(dataWrapper.getCount());
        }
    }

    @Mapper(uses = {DataConverterWithDefault.class})
    public interface WorkaroundMapper2 {

        WorkaroundMapper2 INSTANCE = Mappers.getMapper(WorkaroundMapper2.class);

        @Mapping(target = "name", source = "name")
        @Mapping(target = "quantity", source = "dataWrapper", qualifiedByName = "quantityConverterWithDefault")
        TargetObject convert(SourceObject source);
    }

    // Test main method
    public static void main(String[] args) {
        SourceObject source = new SourceObject();
        source.setName("Test");

        DataWrapper wrapper = new DataWrapper();
        wrapper.setCount(5);
        source.setDataWrapper(wrapper);

        // Test with IssueMapper (will fail to compile)
        // TargetObject target = IssueMapper.INSTANCE.convert(source);

        // Test with WorkaroundMapper1
        TargetObject target1 = WorkaroundMapper1.INSTANCE.convert(source);
        System.out.println("Workaround 1 - Name: " + target1.getName() + ", Quantity: " + target1.getQuantity());

        // Test with WorkaroundMapper2
        TargetObject target2 = WorkaroundMapper2.INSTANCE.convert(source);
        System.out.println("Workaround 2 - Name: " + target2.getName() + ", Quantity: " + target2.getQuantity());

        // Test with null dataWrapper
        source.setDataWrapper(null);
        TargetObject target3 = WorkaroundMapper2.INSTANCE.convert(source);
        System.out.println("Workaround 2 with null - Name: " + target3.getName() + ", Quantity: " + target3.getQuantity());
    }
}