Support merging with mapper annotation

[andriy-dmytruk]

Support merging with @Mapper annotation.

For example, the following method definitions are supported:

@Singleton
@Mapper
abstract class TestMerge {

    @Mapper
    abstract Skeleton merge(SkeletonPartA a, SkeletonPartB b, SkeletonPartC c);

    @Mapper.Mapping(from = "a.halloweenDescription", to = "description")
    @Mapper.Mapping(from = "#{a.deadAge + a.aliveAge}", to = "age")
    abstract Skeleton merge(CustomPart a, SkeletonPartB b, SkeletonPartC c);

    @Mapper
    abstract Skeleton update(Skeleton skeleton, Map<String, Object> values);

    @Mapper.Mapping(from = "values.halloweenDescription", to = "description")
    @Mapper.Mapping(from = "#{skeleton.get('deadAge')}", to = "age")
    abstract Skeleton merge(Map<String, Object> skeleton, Map<String, Object> values);

    @Mapper(mergeStrategy = "EXPLICITLY_SET")
    @Mapper.Mapping(from = "updater.halloweenDescription", to = "description")
    abstract Skeleton updateExplicitlySet(Skeleton current, SkeletonUpdater updater)

    @Mapper(mergeStrategy = Mapper.MERGE_STRATEGY_ALWAYS_OVERRIDE)
    @Mapper.Mapping(from = "updater.halloweenDescription", to = "description")
    abstract Skeleton updateAlwaysOverride(Skeleton current, SkeletonUpdater updater)

    @Mapper(mergeStrategy = Mapper.MERGE_STRATEGY_NOT_NULL_OVERRIDE)
    @Mapper.Mapping(from = "updater.halloweenDescription", to = "description")
    abstract Skeleton updateNotNullOverride(Skeleton current, SkeletonUpdater updater)
}

[sonarcloud]

Quality Gate passed

Issues
7 New issues
0 Accepted issues

Measures
0 Security Hotspots
89.1% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[graemerocher]

Looks good, can you update the docs here as well https://docs.micronaut.io/4.6.5/guide/#beanMappers

[graemerocher]

can this be a record?

[graemerocher]

not sure if this can make it in 4.7 or not. @sdelamo will know

[sdelamo]

not sure if this can make it in 4.7 or not. @sdelamo will know

I will prefer 4.8. I want to deliver 4.7 as soon as possible.

[andriy-dmytruk]

I will prefer 4.8. I want to deliver 4.7 as soon as possible.

4.8 is fine with me. There is no need to rush this change

[graemerocher]

@andriy-dmytruk can you retarget 4.8.x