Suggestion for incorrect repr use

When encountering #[repr = "C"], suggest #[repr(C)] instead of the current #[repr(C, packed, ...)]. We need to detect specific cases like writing #[repr("packed")], where we should suggest #[repr(packed)], as otherwise provide a list of all the valid reprs.

(Follow up to #61140)

Auto merge of #66206 - PotHix:master, r=estebank

Current output:

rust/tests/ui/repr/repr.stderr

Lines 20 to 41 in f5711a5

    
           error[E0539]: malformed `repr` attribute input 
        
             --> $DIR/repr.rs:4:1 
        
              | 
        
           LL | #[repr = "B"] 
        
              | ^^^^^^^^^^^^^ expected this to be a list 
        
              | 
        
              = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html#representations> 
        
           help: try changing it to one of the following valid forms of the attribute 
        
              | 
        
           LL - #[repr = "B"] 
        
           LL + #[repr(<integer type>)] 
        
              | 
        
           LL - #[repr = "B"] 
        
           LL + #[repr(C)] 
        
              | 
        
           LL - #[repr = "B"] 
        
           LL + #[repr(Rust)] 
        
              | 
        
           LL - #[repr = "B"] 
        
           LL + #[repr(align(...))] 
        
              | 
        
              = and 2 other candidates

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Suggestion for incorrect `repr` use #61286

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	error[E0539]: malformed `repr` attribute input
	--> $DIR/repr.rs:4:1
	\|
	LL \| #[repr = "B"]
	\| ^^^^^^^^^^^^^ expected this to be a list
	\|
	= note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html#representations>
	help: try changing it to one of the following valid forms of the attribute
	\|
	LL - #[repr = "B"]
	LL + #[repr(<integer type>)]
	\|
	LL - #[repr = "B"]
	LL + #[repr(C)]
	\|
	LL - #[repr = "B"]
	LL + #[repr(Rust)]
	\|
	LL - #[repr = "B"]
	LL + #[repr(align(...))]
	\|
	= and 2 other candidates

Suggestion for incorrect repr use #61286

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estebank commented on Nov 3, 2025

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Suggestion for incorrect `repr` use #61286