Mapper array to List example

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Hi,

Would be nice to have an example that shows the usage of MapStruct with array (like int[] ) to immutable list with specific add and addAll (like in protobuf).

example:
proto file

message UserDTO {
string id = 1;
string email = 2;
repeated PermissionDTO permissions = 3;
repeated DepartmentDTO main_departments = 4;
repeated DepartmentDTO departments = 5;
}

java file

public class User {

private String id;
private String email;
private Permission[] permissions = new Permission[0];
private List mainDepartments = new ArrayList<>();
private List departments = new ArrayList<>();

public String getId() {
return id;
}

public void setId(String id) {
this.id = id;
}

public String getEmail() {
return email;
}

public void setEmail(String email) {
this.email = email;
}

public Permission[] getPermissions() {
return permissions;
}

public void setPermissions(Permission[] permissions) {
this.permissions = permissions;
}

public List getDepartments() {
return departments;
}

public void setDepartments(List departments) {
this.departments = departments;
}

public List getMainDepartments() {
return mainDepartments;
}

public void setMainDepartments(List mainDepartments) {
this.mainDepartments = mainDepartments;
}
}

Mapper

@Mapper(collectionMappingStrategy = CollectionMappingStrategy.ADDER_PREFERRED,
nullValueCheckStrategy = NullValueCheckStrategy.ALWAYS)
public interface UserMapper {

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

@Mapping(source = "permissions", target = "permissionsList")
@Mapping(source = "mainDepartments", target = "mainDepartmentsList")
@Mapping(source = "departments", target = "departmentsList")
UserDTO map(User user);
}

**Error:**
Can't map property "Permission[] permissions" to "PermissionDTO permissionsList".

**### Desired solution:**

public class UserMapperImpl implements UserMapper {

@Override
public UserDTO map(User user) {
if ( user == null ) {
return null;
}

Builder userDTO = UserDTO.newBuilder();

if ( user.getPermissions() != null ) {
for ( Permission permission : user.getPermissions() ) {
userDTO.addPermissions( map( permission ) );
}
}

...

return userDTO.build();
}
}

or

public class UserMapperImpl implements UserMapper {

@Override
public UserDTO map(User user) {
if ( user == null ) {
return null;
}

Builder userDTO = UserDTO.newBuilder();

if ( user.getPermissions() != null ) {
userDTO.addAllPermissions( map( user.getPermissions()) );
}

...

return userDTO.build();
}
}

**Is it possible to do this with actual release?**

Start from the UserMapper example and the generated UserMapperImpl shown in the issue, then inspect how the protobuf UserDTO builder exposes addPermissions and addAllPermissions. The example is done when it demonstrates mapping the Permission[] source to the protobuf repeated permissions field and includes the corresponding array-to-list behavior requested.

Written by the indexing model from the issue text.