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Inappropriate suggestion when mismatched types occur in the dbg! macro #139253

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jjl9807 opened this issue Apr 2, 2025 · 2 comments · May be fixed by #139399
Open

Inappropriate suggestion when mismatched types occur in the dbg! macro #139253

jjl9807 opened this issue Apr 2, 2025 · 2 comments · May be fixed by #139399
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@xizheyin
Labels
A-diagnostics Area: Messages for errors, warnings, and lints A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..) D-invalid-suggestion Diagnostics: A structured suggestion resulting in incorrect code. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@jjl9807
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jjl9807 commented Apr 2, 2025 •
edited by rustbot
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Code

#[derive(Clone, Debug)]
struct Point<T> {
    v: T,
}

fn main() {
    let a: Point<u8> = dbg!(Point { v: 42 });
    let b: Point<u8> = dbg!(&a);
}

Current output

error[E0308]: mismatched types
  --> test.rs:10:24
   |
10 |     let b: Point<u8> = dbg!(&a);
   |                        ^^^^^^^^ expected `Point<u8>`, found `&Point<u8>`
   |
   = note: expected struct `Point<_>`
           found reference `&Point<_>`
   = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider using clone here
  --> /home/jl-jiang/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/macros.rs:367:20
   |
367|                 tmp.clone()
   |                    ++++++++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0308`.

Desired output

error[E0308]: mismatched types
  --> test.rs:10:24
   |
10 |     let b: Point<u8> = dbg!(&a);
   |                        ^^^^^^^^ expected `Point<u8>`, found `&Point<u8>`
   |
   = note: expected struct `Point<_>`
           found reference `&Point<_>`
   = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider using clone here
  --> test.rs:10:29
   |
10 |     let b: Point<u8> = dbg!(a.clone());
   |                               +++++++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0308`.

Rationale and extra context

No response

Other cases



Rust Version


rustc 1.88.0-nightly (e2014e876 2025-04-01)
binary: rustc
commit-hash: e2014e876e3efaa69bf51c19579adb16c3df5f81
commit-date: 2025-04-01
host: x86_64-unknown-linux-gnu
release: 1.88.0-nightly
LLVM version: 20.1.1


Anything else?


No response






      		
    

      
  





        

            


            

              
            

        

      


      
    








      

    



      

  
            

    

      
    

    


      

          @jjl9807
jjl9807




            added
      

  A-diagnostics

  Area: Messages for errors, warnings, and lints

      

  T-compiler

  Relevant to the compiler team, which will review and decide on the PR/issue.

  labels


      Apr 2, 2025

    

  



    

    

      
    

    


      

          @fmease
fmease




            added
      

  A-macros

  Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..)

      

  D-invalid-suggestion

  Diagnostics: A structured suggestion resulting in incorrect code.

  labels


      Apr 4, 2025

    

  








      

  
      



  

  @fmease





  


    

      

  

    

        
    
    

  


      
          
  
      
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            fmease
  

      

      

      commented


        Apr 4, 2025


      
    


  





      


        


  
    

      
          
Potential fix for this category of issues: Suppress the suggestion if the span is  .in_external_macro(map).

      		
    

  





        


            

            

              
            

        

      


      

            
  

    
  
    
    

  

  



    












      

  
      



  

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            xizheyin
  

      

      

      commented


        Apr 4, 2025


      
    


  





      


        


  
    

      
          
If so, I can repair it.


@rustbot claim

      		
    

  





        


            

            

              
            

        

      


      

            
  

    
  
    
    

  

  



    












      

  
            


  

  

    
  


  

      

    @xizheyin
xizheyin



    linked a pull request
    
      Apr 5, 2025
    

    that will
    close
    this issue





  


  

      
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    @fmease
fmease



    mentioned this issue
    
      Apr 6, 2025
    





  


  

      
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    Labels
  



    

      

    A-diagnostics

  Area: Messages for errors, warnings, and lints
  

    A-macros

  Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..)
  

    D-invalid-suggestion

  Diagnostics: A structured suggestion resulting in incorrect code.
  

    T-compiler

  Relevant to the compiler team, which will review and decide on the PR/issue.








      

  

    

        

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      Suppress the clone_for_ref suggestion in extern macro

    
      xizheyin/rust
    





      
    

  




      

    

  
      

  

    

      3 participants
    

    

        
          @fmease 
        
          @xizheyin 
        
          @jjl9807