ABP Studio 2.1.9 Bug: Code Generation Duplicates Mapperly Mappers in Projects Migrated from AutoMapper #10402

Environment

• ABP Studio Version: 2.1.9
• ABP Framework Version: 10.0.2
• Project Type: Blazor Server
• Mapping Library: Mapperly (migrated from AutoMapper using official migration guide)

Summary

When using ABP Studio to regenerate an entity in a project that was migrated from AutoMapper to Mapperly (following https://abp.io/docs/10.0/release-info/migration-guides/AutoMapper-To-Mapperly), the code generator appends duplicate mapper classes to the bottom of ApplicationMappers.cs instead of detecting and updating the existing Mapperly mapper definitions.

This causes the Mapperly source generator to crash, which cascades into dozens of compilation errors.

Steps to Reproduce

1. Start with an ABP project that originally used AutoMapper (e.g., created with ABP Suite pre-10.0)
2. Migrate to Mapperly following the official migration guide linked above
3. Generate an entity (e.g., Product) with all options enabled — verify the project compiles
4. Open the same entity in ABP Studio and regenerate it (even a minor change like unchecking Excel Export)
5. Build the solution

What Happens

ABP Studio appends new mapper classes at the bottom of [ProjectName]ApplicationMappers.cs, even though Mapperly mappers for the same entity already exist earlier in the file. For example, the file ends up with both:

// Original (already existed, ~line 50)
[Mapper(RequiredMappingStrategy = RequiredMappingStrategy.Target)]
public partial class ProductToProductDtoMapper : MapperBase<Product, ProductDto>
{
    public override partial ProductDto Map(Product source);
    public override partial void Map(Product source, ProductDto destination);
}

// Duplicate appended by ABP Studio (~line 200)
[Mapper]
public partial class ProductToProductDtoMappers : MapperBase<Product, ProductDto>
{
    public override partial ProductDto Map(Product source);
    public override partial void Map(Product source, ProductDto destination);
}

Note: some duplicates use a slightly different class name (trailing "s"), while others use the exact same class name, producing different error types.

This causes the Mapperly source generator to fail entirely with:

CS8785: Generator 'MapperGenerator' failed to generate source. Exception was of type 'InvalidOperationException' with message 'Sequence contains more than one element'

Because the source generator crashes, none of the ~100 mapper classes in the file receive their generated implementations, producing widespread CS8795 errors ("Partial method must have an implementation part because it has accessibility modifiers").

Additional Issue (same regeneration action)

When unchecking features like "Create user interface" and regenerating, ABP Studio correctly removes those methods from the base interface (e.g., IProductsAppService.cs). However, it does not update or warn about .Extended files that override or call the removed methods, causing additional CS0115 and CS1061 errors.

Expected Behavior

1. ABP Studio should detect existing Mapperly mapper classes and update them in-place (or skip if unchanged), not append duplicates
2. When removing methods from the base interface/service, ABP Studio should either update .Extended files or warn the developer about broken references

Suspected Root Cause

I believe ABP Studio's code generator may be looking for AutoMapper-style CreateMap<>() calls in a Profile class to determine whether mappers exist. In a migrated project, those calls have been replaced by Mapperly MapperBase<> classes, which the generator doesn't recognize — so it treats the entity as having no mappers and generates new ones.

Projects created fresh with ABP 10.0+ (where Mapperly is the default) likely don't have this issue because the generator was designed to work with the mapper format it created.

Workaround

Manually revert ApplicationMappers.cs from source control to remove the appended duplicates, then manually fix any .Extended files referencing removed methods.