Commits on Oct 1, 2024

1. Add _Enum! macros to replace _ arms when matching shared enums …

   As the docs currently state about shared enums:
   > Pattern matching with match still works but will require you to write
   > wildcard arms to handle the situation of an enum value that is not
   > one of the listed variants.
   
   This is unfortunate as there is no way to check that all listed enum
   variants are actually handled. IOW this code does not even warn:
   ```
   mod ffi {
       enum Enum {
           A,
           B,
           C = 5,
       }
   }
   
   match t {
       Enum::A => {},
       Enum::B => {},
       _ => {},
   }
   ```
   
   This generates an extra _Enum! macro that matches all the ranges that
   are _not_ listed by the enum. When using that macro instead of the _
   catch-all, we get compile-time errors if we forget to match variants:
   ```
   match t {
       Enum::A => {},
       Enum::B => {},
       _Enum!() => {},
   }
   // Error Enum{ repr: 5 } case not covered
   ```
   
   The generated macro looks like:
   ```
   macro_rules! _Enum {
       () => { Enum{ repr: 4..5 | 6.. } };
       ($i:ident) => { Enum { repr: $i @ 4..5 | 6.. } };
   }
   ```
   
   It can also be used to ergonomically retrieve the inner value in the
   unlisted case:
   ```
   match t {
       Enum::A => {},
       Enum::B => {},
       Enum::C => {},
       _Enum!(value) => panic!("Unexpected Enum value {value}"),
   }
   ```

   

   nicolas-guichard committed Oct 1, 2024
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