许杰友 Jieyou Xu (Joe) 8da09aed94
Add allow-by-default lint for unit bindings
This lint is not triggered if any of the following conditions are met:

- The user explicitly annotates the binding with the `()` type.
- The binding is from a macro expansion.
- The user explicitly wrote `let () = init;`
- The user explicitly wrote `let pat = ();`. This is allowed for local
  lifetimes.
2023-11-20 11:45:44 +08:00
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