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Swift should allow multiple SWIFT_CONFORMS_TO_PROTOCOL attributes on a C++ class #75831

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egorzhdan opened this issue Aug 12, 2024 · 2 comments · May be fixed by #76204
Open

Swift should allow multiple SWIFT_CONFORMS_TO_PROTOCOL attributes on a C++ class #75831

egorzhdan opened this issue Aug 12, 2024 · 2 comments · May be fixed by #76204
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. c++ interop Feature: Interoperability with C++ compiler The Swift compiler itself good first issue Good for newcomers

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@egorzhdan
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Description

swift/bridging header defines a SWIFT_CONFORMS_TO_PROTOCOL macro, which expands to __attribute__((swift_attr("conforms_to:MyModule.MyProtocol"))).

This attribute lets the Swift compiler know that the annotated C++ class should be automatically marked as conforming to a Swift protocol with the given name.

Currently the Swift compiler only respects one SWIFT_CONFORMS_TO_PROTOCOL attribute on a single C++ class at a time. This is a limitation, we should support multiple SWIFT_CONFORMS_TO_PROTOCOL attributes on a single class.

Reproduction



Expected behavior


If two or more SWIFT_CONFORMS_TO_PROTOCOL attributes are provided, Swift should conform the C++ type to all of the listed Swift protocols.


Environment


Recent Swift compiler from main


Additional information


This is the part of ClangImporter that handles explicit conformances:



  

    

      swift/lib/ClangImporter/ImportDecl.cpp
    

    

        Lines 2840 to 2842
      in
      375363a
    

  

  

    


        

          
           void 
        


        

          
           addExplicitProtocolConformances(NominalTypeDecl *decl, 
        


        

          
                                           const clang::CXXRecordDecl *clangDecl) { 
        

    

  






This method would likely need to change as part of the resolution of this issue.

      		
    

      
  





        



            

              
            

        

      


      
    








      

    



      

  
            

    

      
    

    


      

          @egorzhdan
egorzhdan




            added
      

  bug

  A deviation from expected or documented behavior. Also: expected but undesirable behavior.

      

  c++ interop

  Feature: Interoperability with C++

      

  compiler

  The Swift compiler itself

      

  good first issue

  Good for newcomers

  labels


      Aug 12, 2024

    

  








      

  
      



  

  @jz709u





  


    

      

  

    

        
    
    

  


      
          
  
      
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            jz709u
  

      

      

      commented


        Aug 21, 2024


      
    


  





      


        


  
    

      
          
I am working on this issue.  I have a solution already, but still testing it

      		
    

  





        


            

            

              
            

        

      


      

            
  

    
  
    
    

  

  



    












      

  
      



  

  @jz709u





  


    

      

  

    

        
    
    

  


      
          
  
      
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            jz709u
  

      

      

      commented


        Aug 24, 2024


      
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I have been working on validating my solution.

It's been difficult as I can't do one-off toolchain builds based on this thread:

https://forums.swift.org/t/cant-build-toolchain/70247


I have resorted to validating my solution using the build-script tool and attempting to test it via unit tests.  I can't find the corresponding unit tests which test this part of the code.


I would appreciate it if someone could point me in the right direction on the quickest way to test your solutions.

Thanks again

      		
    

  





        


            

            

              
            

        

      


      

            
  

    
  
    
    

  

  



    












      

  
          

  

    
  


  

      

    @jz709u
jz709u



    linked a pull request
    
      Sep 1, 2024
    

    that will
    close
    this issue





  


  

      
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    bug

  A deviation from expected or documented behavior. Also: expected but undesirable behavior.
  

    c++ interop

  Feature: Interoperability with C++
  

    compiler

  The Swift compiler itself
  

    good first issue

  Good for newcomers








      

  

    

        

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      [C++Interop] Allow Multiple SWIFT_CONFORMS_TO_PROTOCOL to C++ Classes

    
      jz709u/swift
    





    
  




        
      

    

  
      

  

    

      2 participants
    

    

        
          @egorzhdan 
        
          @jz709u