Preemptive comment: the following output towards the second half:

    help: function arguments must have a statically known size, borrowed types always have a known size
      |
    3 | fn f<T>(&t: T)
      |         ^

is a bug that already has a PR to fix. It's supposed to point at the T and suggest the following instead:

    help: function arguments must have a statically known size, borrowed types always have a known size
      |
    3 | fn f<T>(t: &T)
      |            ^