Commits on Nov 6, 2021

1. Suggest dereference of Box when inner type is expected …

   For example:
   
       enum Ty {
           Unit,
           List(Box<Ty>),
       }
   
       fn foo(x: Ty) -> Ty {
           match x {
               Ty::Unit => Ty::Unit,
               Ty::List(elem) => foo(elem),
           }
       }
   
   Before, the only suggestion was to rewrap `elem` with `Ty::List`,
   which is unhelpful and confusing:
   
       error[E0308]: mismatched types
        --> src/test/ui/suggestions/boxed-variant-field.rs:9:31
         |
       9 |         Ty::List(elem) => foo(elem),
         |                               ^^^^
         |                               |
         |                               expected enum `Ty`, found struct `Box`
         |                               help: try using a variant of the expected enum: `Ty::List(elem)`
         |
         = note: expected enum `Ty`
                  found struct `Box<Ty>`
   
   Now, rustc will first suggest dereferencing the `Box`, which is most
   likely what the user intended:
   
       error[E0308]: mismatched types
        --> src/test/ui/suggestions/boxed-variant-field.rs:9:31
         |
       9 |         Ty::List(elem) => foo(elem),
         |                               ^^^^ expected enum `Ty`, found struct `Box`
         |
         = note: expected enum `Ty`
                  found struct `Box<Ty>`
       help: try dereferencing the `Box`
         |
       9 |         Ty::List(elem) => foo(*elem),
         |                               +
       help: try using a variant of the expected enum
         |
       9 |         Ty::List(elem) => foo(Ty::List(elem)),
         |                               ~~~~~~~~~~~~~~

   

   camelid committed Nov 6, 2021
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