8000 Bug: Duplicate `extends` clause for `interface` should be reported · Issue #11077 · typescript-eslint/typescript-eslint · GitHub
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Open
4 tasks done
leaysgur opened this issue Apr 15, 2025 · 3 comments
Open
4 tasks done

Bug: Duplicate extends clause for interface should be reported #11077

leaysgur opened this issue Apr 15, 2025 · 3 comments
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accepting prs Go ahead, send a pull request that resolves this issue AST PRs and Issues about the AST structure bug Something isn't working package: typescript-estree Issues related to @typescript-eslint/typescript-estree

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@leaysgur
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Before You File a Bug Report Please Confirm You Have Done The Following...

  • I have tried restarting my IDE and the issue persists.
  • I have updated to the latest version of the packages.
  • I have searched for related issues and found none that matched my issue.
  • I have read the FAQ and my problem is not listed.

Relevant Package

typescript-estree

Playground Link

https://typescript-eslint.io/play/#ts=5.4.3&fileType=.tsx&code=MYGwhgzhAECiCM0DeBfAUKSNYCZno3CmgA1EBTADwBdyA7AE20VTQHo3pNiS8rbGzaP3pM4eVtxgkAzNACWAWwAOIcovrUhrDlyLSALApVqNdLXERLV6zdgnoppAKzCaooddN3x%2BdpycSADZjGzMLBDcBMVw-NHlzcgAnADMwYHJoAE0Kd0FLPwTaVPTMrL48mNzo%2B3xoXUBeDcABHegAFQALeRgIdoB7AFcQBmgAI0yk8mVepNphkYBPaGUwJIhkgBpoEHkAa0ze6nbkiH8FRJKM7LkvW3NtdF0i5LTLrKMb8M8TW4iHU6eLmVXB8fJERPlYjpOACXmUQuCqqFvHdfKggA&eslintrc=N4KABGBEBOCuA2BTAzpAXGYBfEWg&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=false

Repro Code

class E1 {}
class E2 {}

// class X2 extends E1 extends E2 {} // This is reported
interface Y2 extends E1 extends E2 {} // This is NOT reported

ESLint Config



tsconfig




Expected Result


Parser should report internal error TS1172: 'extends' clause already seen. like TS does.


https://www.typescriptlang.org/play/?#code/MYGwhgzhAECiCM0DeBfAUKSNYCZno3CmgA1EBTADwBdyA7AE20VTQHo3pNiS8rbGzaP3pM4eVtxgkAzNACWAWwAOIcovrUhrDlyLSALApVqNdLXERLV6zdgnoppAKzCaooddN3x+dpycSADZjGzMLBDcBMVw-NHlzcgAnADMwYHJoAE0Kd0FLPwTaVPTMrL48mNzo+z9dIuS0jOy5L1tzbXR6xJLmrKM28M8TdoiHfwUeprLXQZ9IkXzYnU4G3rKQxarQ7w7fVCA


Actual Result


No errors are reported.


Additional Info


Since duplicate extends are reported correctly for class, they should be reported for interface too?



  

    

      typescript-eslint/packages/typescript-estree/src/convert.ts
    

    

        Lines 2043 to 2049
      in
      7f32763
    

  

  

    


        

          
           if (token === SyntaxKind.ExtendsKeyword) { 
        


        

          
             if (extendsClause) { 
        


        

          
               this.#throwUnlessAllowInvalidAST( 
        


        

          
                 heritageClause, 
        


        

          
                 "'extends' clause already seen.", 
        


        

          
               ); 
        


        

          
             } 
        

    

  






I can send a PR if this is acceptable change.


leaysgur@0a6d4db


Versions







package
version






@typescript-eslint/typescript-estree
8.30.1





      		
    

      
  





        



            
            

              
            

        

      


      
    








      

    



      

  
            

    

      
    

    


      

          @leaysgur
leaysgur




            added
      

  bug

  Something isn't working

      

  triage

  Waiting for team members to take a look

  labels


      Apr 15, 2025

    

  








      

  
      



  

  @bradzacher





  


    

      

  

    

        
    
    

  


      
          
  
      
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I would direct you towards my reply on your last issue #11064 (comment)


TS allows a myriad of combinations of invalid syntax - most of which we don't explicitly fail on either. Linting code with any TS errors is considered "undefined behaviour".


The reason we have errors for classes is because there's some syntactical ordering to classes that should hold true - eg implements comes after extends - and us implementing the checks was easier than downstream consumers like prettier implementing the checks. And considering we were adding a few checks adding more was easy and made sense.


It's really a question of what is to be gained from adding the errors. Why do you think this should be an explicit and hard crash?

      		
    

  





        


            

            
            

              
            

        

      


      

            
  

    
  
    
    

  

  


    












      

  
            

    

      
    

    


      

          @bradzacher
bradzacher




            added
      

  package: typescript-estree

  Issues related to @typescript-eslint/typescript-estree

      

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    and removed
      

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      Apr 15, 2025

    

  








      

  
      



  

  @leaysgur





  


    

      

  

    

        
    
    

  


      
          
  
      
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            leaysgur
  

      

      

      commented


        Apr 16, 2025


      
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Thank you for your continued kindness. 🙏




Why do you think this should be an explicit and hard crash?




This was motivated by:


    

  • For interface
    • 

  • duplicate implements are reported as internal error
    • 

  • But, why duplicate extends are not?
    • 



I was simply concerned about these difference.


(If you feel this is a kind of maintenance burden, feel free to close this. Sorry in that case.)

      		
    

  





        


            

            
            

              
            

        

      


      

            
  

    
  
    
    

  

  


    












      

  
          

  

    
  


  

      

    @bradzacher
bradzacher



    mentioned this issue
    
      Apr 18, 2025
    





  


  

      
  
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          @JoshuaKGoldberg
JoshuaKGoldberg




        changed the title
Bug: Duplicate extends caluse for interface should be reported

Bug: Duplicate extends clause for interface should be reported


      Apr 18, 2025

    

  



    

    

      
    

    


      

          @JoshuaKGoldberg
JoshuaKGoldberg




            added
      

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      Apr 18, 2025

    

  








      

  
      



  

  @JoshuaKGoldberg





  


    

      

  

    

        
    
    

  


      
          
  
      
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Agreed. As with #11088, 👍 from me on adding slightly more sanitization to the AST.

      		
    

  





        


            

            
            

              
            

        

      


      

            
  

    
  
    
    

  

  


    












      

  
            

    

      
    

    


      

          @JoshuaKGoldberg
JoshuaKGoldberg




            added
      

  accepting prs

  Go ahead, send a pull request that resolves this issue

    and removed
      

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      May 19, 2025

    

  












  
  

    

      

  





  




  
  

              

  
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          @leaysgur 
        
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